CCNet 100/2003 - 7 November 2003

By 2050, approximately 10 billion people will live on Earth demanding
~5 times the power now available. By then, solar power from the Moon could
provide everyone clean, affordable, and sustainable electric power. No
terrestrial options can provide the needed minimum of 2 kWe/person or at
least 20 terawatts globally.... By 2050, the LSP System would allow all
human societies to prosper while nurturing rather than consuming the biosphere.
      --David R. Criswell, Institute for Space Systems Operations, 6 November 2003

Of all the scientific benefits of Apollo, appreciation of the importance
of impact, or the collision of solid bodies, in planetary evolution must
rank highest. Additional knowledge still resides [on the Moon]; while the
Earth's surface record has been largely erased by the dynamic processes of
erosion and crustal recycling, the ancient lunar surface retains this impact
history. When we return to the Moon, we will examine this record in detail
and learn about its evolution as well as our own.
     --Paul D. Spudis, Lunar and Planetary Institute, 6 November 2003

    David R. Criswell, Institute for Space Systems Operations

    Harrison H Schmitt, 6 November 2003

    Paul D. Spudis, Lunar and Planetary Institute

    Roger Angel, Testimony for Senate hearing on Lunar Exploration, November 6th 2003

    CNN, 6 November 2003


US Senate Committee on Science, Technology and Transportation, 6 November 2003

Testimony of Dr. David R. Criswell at Senate Commerce, Science, and Transportation
Subcommittee on Science, Technology, and Space Hearings: "Lunar Exploration"

Thursday, November 6, 2003, 2:30 PM - SR-253

Dr. David R. Criswell, Director, Institute for Space Systems Operations,
University of Houston and University of Houston-Clear Lake

Mr. Chairman and Members of the Subcommittee:

I am honored to have this opportunity to introduce a program for the economic and
environmental security for Earth, and especially for the  United States of America, by
meeting Earth's real electrical power needs.

By 2050, approximately 10 billion people will live on Earth demanding ~5 times the
power now available. By then, solar power from the Moon could provide everyone
clean, affordable, and sustainable electric power. No terrestrial options can provide the
needed minimum of 2 kWe/person or at least 20 terawatts globally.

Solar power bases will be built on the Moon that collect a small fraction of the Moon's
dependable solar power and convert it into power beams that will dependably deliver
lunar solar power to receivers on Earth. On Earth each power beam will be transformed
into electricity and distributed, on-demand, through local electric power grids. Each
terrestrial receiver can accept power directly from the Moon or indirectly, via relay
satellites, when the receiver cannot view the Moon. The intensity of each power beam is
restricted to 20%, or less, of the intensity of noontime sunlight. Each power beam can be
safely received, for example, in an industrially zoned area.

The Lunar Solar Power (LSP) System does not require basic new technological
developments. Adequate knowledge of the Moon and the essential technologies have
been available since the late 1970s to design, build, and operate the LSP System.
Automated machines and people would be sent to the Moon to build the lunar power
bases. The machines would build the power components from the common lunar dust
and rocks, thereby avoiding the high cost of transporting materials from the Earth to the
Moon. The LSP System is distributed and open. Thus, it can readily accommodate new
manufacturing and operating technologies as they become available.

Engineers, scientists, astronauts, and managers skilled in mining, manufacturing,
electronics, aerospace, and industrial production of commodities will create new wealth
on the Moon. Thousands of tele-robotic workers in American facilities, primarily on
Earth, will oversee the lunar machinery and maintain the LSP System.

Our national space program, in cooperation with advanced U.S. industries, can produce
the LSP System for a small fraction of the cost of building equivalent power generating
capabilities on Earth. Shuttle- and Space Station-derived systems and LSP production

machinery can be in operation in space and on the Moon within a few years. A
demonstration LSP System can grow quickly to 50% of averaged U.S. electric
consumption, ~0.2 TWe, within 15 years and be profitable thereafter. When LSP
provides 20 terawatts of electric power to Earth it can sell the electricity at one-fifth of
today's cost or ~1 ¢/kWe-h. At current electric prices LSP would generate ~9 trillion
dollars per year of net income.

Like hydroelectric dams, every power receiver on Earth can be an engine of clean
economic growth. Gross World Product can increase a factor of 10. The average annual
per capita income of Developing Nations can increase from today's $2,500 to ~$20,000.
Economically driven emigrations, such as from Mexico and Central America to the
United States, will gradually decrease.

Increasingly wealthy Developing Nations will generate new and rapidly growing markets
for American goods and services. Lunar power can generate hydrogen to fuel cars at low
cost and with no release of greenhouse gases. United States payments to other nations for
oil, natural gas, petrochemicals, and commodities such as fertilizer will decrease. LSP
industries will establish new, high-value American jobs. LSP will generate major
investment opportunities for Americans. The average American income could increase
from today's ~$35,000/y-person to more than $150,000/y-person.

By 2050, the LSP System would allow all human societies to prosper while nurturing
rather than consuming the biosphere.

Respectfully submitted,

Dr. David R. Criswell, Director, Institute for Space Systems Operations, University of
Houston and University of Houston-Clear Lake, Houston, TX
The Lunar Solar Power System and its general benefits are described in the attached fourpage

Additional papers are available on these websites and via search engines (search on
"David R. Criswell" or "Lunar Solar Power"):

The Industrial Physicist

The World Energy Congress (17th and 18th)


Harrison H Schmitt, 6 November 2003


P.O. Box 90730
Albuquerque, NM 87199
505 823 2616


NOVEMBER 6, 2003

A return to the Moon to stay would be at least comparable to the first permanent settlement of America if not to the movement of our species out of Africa.

I am skeptical that the U.S. Government can be counted on to make such a "sustained commitment" absent unanticipated circumstances comparable to those of the late 1950s and early 1960s.  Therefore, I have spent much of the last decade exploring what it would take for private investors to make such a commitment. At least it is clear that investors will stick with a project if presented to them with a credible business plan and a rate of return commensurate with the risk to invested capital. My colleagues at the Fusion Technology Institute of the University of Wisconsin-Madison and the Interlune-Intermars Initiative, Inc. believe that such a commercially viable project exists in lunar helium-3 used as a fuel for fusion electric power plants on Earth.

Lunar helium-3, arriving at the Moon as part of the solar wind, is imbedded as a trace, non-radioactive isotope in the lunar soils.  There is a resource base of helium-3 about of 10,000 metric tonnes just in upper three meters of the titanium-rich soils of Mare Tranquillitatis.  The energy equivalent value of Helium-3 delivered to operating fusion power plants on Earth would be about $4 billion per tonne relative to today's coal.  Coal, of course, supplies about half of the approximately $40 billion domestic electrical power market.

A business and investor based approach to a return to the Moon to stay represents a clear alternative to initiatives by the U.S. Government or by a coalition of other countries.  A business-investor approach, supported by the potential of lunar Helium-3 fusion power, and derivative technologies and resources, offers the greatest likelihood of a predictable and sustained commitment to a return to deep space.


P.O. Box 90730
Albuquerque, NM 87199
505 823 2616


NOVEMBER 6, 2003


The Apollo 17 mission on which I was privileged to fly in December 1972 was the most recent visit by human beings to the Moon, indeed to deep space.  A return by Americans to the Moon at least 40 years after the end of the Apollo 17 mission probably would represent a commitment to return to stay. Otherwise, it is hard to imagine how a sustained commitment to return would develop in this country. 

I must admit to being skeptical that the U.S. Government can be counted on to make such a "sustained commitment" absent unanticipated circumstances comparable to those of the late 1950s and early 1960s. Therefore, I have spent much of the last decade exploring what it would take for private investors to make such a commitment. At least it is clear that investors will stick with a project if presented to them with a credible business plan and a rate of return commensurate with the risk to invested capital. My colleagues at the Fusion Technology Institute of the University of Wisconsin-Madison and the Interlune-Intermars Initiative, Inc. believe that such a commercially viable project exists in lunar helium-3 used as a fuel for fusion electric power plants on Earth.

Global demand and need for energy will likely increase by at least a factor of eight by the mid-point of the 21st Century. This factor represents the total of a factor of two to stay even with population growth and a factor of four or more to meet the aspirations of people who wish to significantly improve their standards of living.  There is another unknown factor that will be necessary to mitigate the adverse effects of climate change, whether warming or cooling, and the demands of new, energy intensive technologies.  

Helium has two stable isotopes, helium 4, familiar to all who have received helium-filled baloons, and the even lighter helium 3.  Lunar helium-3, arriving at the Moon as part of the solar wind, is imbedded as a trace, non-radioactive isotope in the lunar soils.  It represents one potential energy source to meet this century's rapidly escalating demand.  There is a resource base of helium-3 of about 10,000 metric tonnes just in upper three meters of the titanium-rich soils of Mare Tranquillitatis.  This was the landing region for Neil Armstrong and Apollo 11 in 1969.  The energy equivalent value of Helium-3 delivered to operating fusion power plants on Earth would be about $4 billion per tonne relative to today's coal.  Coal, of course, supplies about half of the approximately $40 billion domestic electrical power market.  These numbers illustrate the magnitude of the business opportunity for helium-3 fusion power to compete for the creation of new electrical capacity and the replacement of old plant during the 21st Century.

Past technical activities on Earth and in deep space provide a strong base for initiating this enterprise.  Such activities include access to and operations in deep space as well as the terrestrial mining and surface materials processing industries.  Also, over the last decade, there has been historic progress in the development of inertial electrostatic confinement (IEC) fusion at the University of Wisconsin-Madison.  Progress there includes the production of over a milliwatt of steady-state power from the fusion of helium-3 and deuterium.  Steady progress in IEC research as well as basic physics argues strongly that the IEC approach to fusion power has significantly more commercial viability than other technologies pursued by the fusion community. 

It will have inherently lower capital costs, higher energy conversion efficiency, a range of power from a few hundred megawatts upward, and little or no associated radioactivity or radioactive waste.  It should be noted, however, that IEC research has received no significant support as an alternative to Tokamak-based fusion from the Department of Energy in spite of that Department's large fusion technology budgets.  The Office of Science and Technology Policy under several Administrations also has ignored this approach.

On the question of international law relative to outer space, specifically the Outer Space Treaty of 1967, that law is permissive relative to properly licensed and regulated commercial endeavors.  Under the 1967 Treaty, lunar resources can be extracted and owned, but national sovereignty cannot be asserted over the mining area.  If the Moon Agreement of 1979, however, is ever submitted to the Senate for ratification, it should be deep sixed.  The uncertainty that this Agreement would create in terms of international management regimes would make it impossible to raise private capital for a return to the Moon for helium-3 and would seriously hamper if not prevent a successful initiative by the United States Government.

The general technologies required for the success of this enterprise are known.  Mining, extraction, processing, and transportation of helium-3 to Earth requires innovations in engineering, particularly in light-weight, robotic mining systems, but no known new engineering concepts.  By-products of lunar helium-3 extraction, largely hydrogen, oxygen, and water, have large potential markets in space and ultimately will add to the economic attractiveness of this business opportunity.  Inertial electrostatic confinement (IEC) fusion technology appears be the most attractive and least capital intensive approach to terrestrial fusion power plants, although engineering challenges of scaling remain for this technolgy.  Heavy lift launch costs comprise the largest cost uncertainty facing initial business planning, however, many factors, particularly long term production contracts, promise to lower these costs into the range of $1-2000 per kilogram versus about $70,000 per kilogram fully burdened for the Apollo Saturn V rocket.

A business enterprise based on lunar resources will be driven by cost considerations to minimize the number of humans required for the extraction of each unit of resource.  Humans will be required, on the other hand, to prevent costly breakdowns of semi-robotic mining, processing, and delivery systems, to provide manual back-up to robotic or tele-robotic operation, and to support human activities in general.  On the Moon, humans will provide instantaneous observation, interpretation, and assimilation of the environment in which they work and in the creative reaction to that environment.  Human eyes, experience, judgement, ingenuity, and manipulative capabilities are unique in and of themselves and highly additive in synergistic and spontaneous interaction with instruments and robotic systems (see Appendix A). 

Thus, the next return to the Moon will approach work on the lunar surface very pragmatically with humans in the roles of exploration geologist, mining geologist/engineer, heavy equipment operator/engineer, heavy equipment/robotic maintenance engineer, mine manager, and the like.  During the early years of operations the number of personnel will be about six per mining/processing unit plus four support personnel per three mining/processing units.  Cost considerations also will drive business to encourage or require personnel to settle, provide all medical care and recreation, and conduct most or all operations control on the Moon.

The creation of capabilities to support helium-3 mining operations also will provide the opportunity to support NASA's human lunar and planetary research at much reduced cost, as the cost of capital for launch and basic operations will be carried by the business enterprise.  Science thus will be one of several ancillary profit centers for the business, but at a cost to scientists much below that of purely scientific effort to return to the Moon or explore Mars.  Technology and facilities required for success of a lunar commercial enterprise, particularly heavy lift launch and fusion technologies, also will enable the conduct, and reduce the cost of many space activities in addition to science.  These include exploration and settlement of Mars, asteroid interception and diversion, and various national security initiatives. 

It is doubtful that the United States or any government will initiate or sustain a return of humans to the Moon absent a comparable set of circumstances as those facing the Congress and Presidents Eisenhower, Kennedy, and Johnson in the late 1950s and throughout 1960s.  Huge unfunded "entitlement" liabilities and a lack of sustained media and therefore public interest will prevent the long-term commitment of resources and attention that such an effort requires.  Even if tax-based funding commitments could be guaranteed, it is not a foregone conclusion that the competent and disciplined management system necessary to work in deep space would be created and sustained. 

If Government were to lead a return to deep space, the NASA of today is probably not the agency to undertake a significant new program to return humans to deep space, particularly the Moon and then to Mars. NASA today lacks the critical mass of youthful energy and imagination required for work in deep space.  It also has become too bureaucratic and too risk-adverse.  Either a new agency would needed to implement such a program or NASA would need to be totally restructured using the lessons of what has worked and has not worked since it was created 45 years ago.  Of particular importance would be for most of the agency to be made up of engineers and technicians in their 20s and managers in their 30s, the re-institution of design engineering activities in parallel with those of contractors, and the streamlining of management responsibility.  The existing NASA also would need to undergo a major restructuring and streamlining of its program management, risk management, and financial management structures.  Such total restructuring would be necessary to re-create the competence and discipline necessary to operate successfully in the much higher risk and more complex deep space environment relative to that in near-earth orbit.
Most important for a new NASA or a new agency would be the guarantee of a sustained political (financial) commitment to see the job through and to not turn back once a deep space operational capability exists once again or accidents happen.  At this point in history, we cannot count on the Government for such a sustained commitment.  This includes not under-funding the effort - a huge problem still plaguing the Space Shuttle, the International Space Station, and other current and past programs.  That is why I have been looking to a more predictable commitment from investors who have been given a credible business plan and a return on investment commensurable with the risk.

Attaining a level of sustaining operations for a core business in fusion power and lunar resources requires about 10-15 years and $10-15 billion of private investment capital as well as the successful interim marketing and profitable sales related to a variety of applied fusion technologies.  The time required from start-up to the delivery of the first 100 kg years supply to the first operating 1000 megawatt fusion power plant on Earth will be a function of the rate at which capital is available, but probably no less than 10 years.  This schedule also depends to some degree on the U.S. Government being actively supportive in matters involving taxes, regulations, and international law but no more so than is expected for other commercial endeavors.  If the U.S. Government also provided an internal environment for research and development of important technologies, investors would be encouraged as well.  As you are aware, the precursor to NASA, the National Advisory Committee on Aeronautics (NACA), provided similar assistance and antitrust protection to aeronautics industry research during most of the 20th Century.

In spite of the large, long-term potential return on investment, access to capital markets for a lunar 3He and terrestrial fusion power business will require a near-term return on investment, based on early applications of IEC fusion technology (10).  Business plan development for commercial production and use of lunar Helium-3 requires a number of major steps all of which are necessary if long investor interest is to be attracted and held to the venture.  The basic lunar resource endeavor would require a sustained commitment of investor capital for 10 to 15 years before there would be an adequate return on investment, far to long to expect to be competitive in the world's capital markets.  Thus, "business bridges" with realistic and competitive returns on investment in three to five years will be necessary to reach the point where the lunar energy opportunity can attract the necessary investment capital.  They include PET isotope production at point-of-use, therapeutic medical isotope production independent of fission reactors, nuclear waste transmutation, and mobile land mine and other explosive detection.  Once fusion energy breakeven is exceeded, mobile, very long duration electrical power sources will be possible.  These business bridges also should advance the development of the lunar energy technology base if at all possible.

A business and investor based approach to a return to the Moon to stay represents a clear alternative to initiatives by the U.S. Government or by a coalition of other countries.  Although not yet certain of success, a business-investor approach, supported by the potential of lunar Helium-3 fusion power, and derivative technologies and resources, offers the greatest likelihood of a predictable and sustained commitment to a return to deep space.


The term "space exploration" implies the exploration of the Moon, planets and asteroids, that is, "deep space," in contrast to continuing human activities in Earth orbit.  Human activities in Earth orbit have less to do with exploration and more to do with international commitments, as in the case of the Space Station, and prestige and technological development, as in the case of China and Russia.  There are also research opportunities, not fully recognized even after 40 years, that exploit the opportunities presented by being in Earth orbit.

Deep space exploration has been and should always be conducted with the best combination of human and robotic techniques.  Many here will argue the value of robotics.  I will just say that any data collection that can be successfully automated at reasonable cost should be.  In general, human being's should not waste their time with activities such as surveying, systematic photography, and routine data collection. Robotic precursors into situations of undefined or uncertain risk also are clearly appropriate.

Direct human exploration, however, offers exceptional benefits that robotic exploration currently cannot and probably will not duplicate in the foreseeable future, certainly not at competitive costs.  What we are really talking about here is the value of field geology.  Many of my scientific colleagues, including the late Carl Sagan, have made the argument that everything we learned scientifically from Apollo exploration could have been done roboticly.  Not only do the facts not support this claim, but such individuals and groups have never been forced to cost out such a robotic exploration program.  I submit that robotic duplication of the vast scientific return of human exploration of six sites on the Moon would cost far more that the approximately $7 billion spent on science and probably more than the $100 million total cost of Apollo.  Those are estimates in today's dollars.

What do human's bring to the table?

First, there is the human brain - a semi-quantitative super computer, with hundreds of millions years of research and development behind it and several million years of accelerated refinement based on the requirements for survival of our genus.  This brain is both programmable and instantly re-programmable on the basis of training, experience, and preceding observations.

Second, there are the human eyes - a high resolution, stereo optical system of extraordinary dynamic range that also have resulted from hundreds of millions of years of trial and error.  Integrated with the human brain, this system continuously adjusts to the changing optical and intellectual environment encountered during exploration of new situations.  In that sense, field geological and biological exploration is little different from many other types of scientific research where integration of the eyes and brain are essential parts of successful inquires into the workings of Nature.

Third, there are the human hands - a highly dexterous and sensitive bio-mechanical system also integrated with the human brain as well as the human eyes and also particularly benefiting from several million years of recent development.  We so far have grossly underutilized human hands during space exploration, but the potential is there to bring them fully to bear on future activities possibly through integration with robotic extensions or micro-mechanical device integration into gloves.

Fourth, there are human emotions - the spontaneous reaction to the exploration environment that brings creativity to bear on any new circumstance, opportunity, or problem.  Human emotions also are the basis for public interest in support of space exploration, interest beyond that which can be engendered by robotic exploration.  Human emotions further create the very special bond that space exploration has with young people, both those of all ages in school and those who wish to participate directly in such exploration.

Fifth, there is the natural urge of the human species to expand its accessible habitats and thus enhance the probability of its long-term survival.  Deep space exploration by humans provides the foundations for long-term survival through the settlement of the Moon and Mars in this century and the Galaxy in the next.

Finally, there is a special benefit to deep space exploration by Americans - the continual transplantation of the institutions of freedom to those human settlements on the Moon and Mars.  This is our special gift and our special obligation to the future.


1. Schmitt, H. H., Journal of Aerospace Engineering, April 1997, pp 60-67.
2. Wittenberg, L. J., and co-workers, Fusion Technology, 1986, 10, pp 167-178.
3. Johnson, J. R., Geophysical Research Letter, 26, 3, 1999, pp 385-388.
4. Cameron, E. N., Helium Resources of MareTranquillitatis, Technical Report, WCSAR-TR-AR3-9207-1, 1992.
5. Kulcinski, G. L., and Schmitt, H. H., 1992, Fusion Technology, 21, p. 2221.
6. Feldman, W. C., and co-workers, Science, 281, 1998, pp 1496-1500.
7. Schmitt, H. H., in Mark, H., Ed., Encyclopedia of Space, 2003, Wiley, New York.
8. Kulcinski, G. L., 1993, Proceedings, 2nd Wisconsin Symposium on Helium-3 and Fusion Power, WCSAR-TR-AR3-9307-3.
9. Schmitt, H. H., 1998, Space 98, Proceedings of the Conference, p. 1-14.
10. Kulcinski, G. L. 1996, Proceedings, 12th Topical Meeting on the Technology of Fusion Power, UWFDM-1025.


Paul D. Spudis, Lunar and Planetary Institute

Testimony of Dr. Paul D. Spudis at the Subcommittee on Science, Technology, and Space, Senate Commerce, Science, and Transportation Committee hearing on "Lunar Exploration"

Dr. Paul D. Spudis
Planetary Scientist
Lunar and Planetary Institute
November 6, 2003

Mr. Chairman and members of the committee, thank you for inviting me here today to testify on the subject of lunar exploration and the US space program.

I want to discuss a new destination for America in space - the Moon. Although we conducted our initial visits to that body over 30 years ago, we have recently made several important discoveries that indicate a return to the Moon offers many advantages and benefits to the nation.  In addition to being a scientifically rich object for study, the Moon offers abundant material and energy resources, the feedstock of an industrial space infrastructure. Once established, such an infrastructure will revolutionize space travel, assuring us of continuous, routine access to cislunar space (i.e., the space between and around Earth and Moon) and beyond. The value of the Moon as a space destination has not escaped the notice of other countries -  at least four new robotic missions are currently being flown or prepared by Europe, India, Japan, and China and advanced planning for human missions in many of these countries is already underway.

With me here today is Dr. Bill Stone, a prominent explorer and expedition leader. The points which I will present represent our joint thinking as to WHY the nation needs to return to the Moon and why that return should take place NOW rather than later.

(1)NASA needs a politically viable mission and both Shuttle and ISS are losing appeal as "space exploration." America needs a compelling space program!

Forty years ago, America made a decision to go to the Moon, starting from a state of primitive technology and vast ignorance. We accomplished this great feat within 8 years, giving us for the first time the ability to travel to another world.  We now have a commercial launch industry that each year lifts a mass equivalent to an Apollo mission to geosynchronous orbit. Its mission accomplished, NASA looked to other programs to keep the dream of space flight alive. Shuttle was presented as an affordable means to low Earth orbit. Space Station was planned as both a laboratory in orbit and a way station to the rest of the Solar System. Meanwhile, the Moon largely was ignored as an object worthy of study in its own right, as a natural space station to provision and enable space flight farther a field, and as a center of commerce and national security.

NASA's current problems are partly technical, but mostly related to the fact that it no longer has a mission, as in its early "Days of Glory." Forty years ago, its mission was to beat the Soviets to the Moon, a clear goal articulated by the national leadership and presented with a deadline (by the end of the decade). Now, the agency looks for a mission, but has yet to find one, at least, one perceived by government and the American people as worthy of long-term commitment. In the absence of such a goal, we drift between projects and have some success, but nothing is cumulative, where each step builds upon and extends the capability of the step preceding it.

A new national focus in space must have a direct and clear benefit to the American public.  Pure science and the search for life are not defensible justifications. As Dr. Stone has put it recently, what the nation needs is a Lewis and Clark-class mission - one that opens the frontier to the expansion of the external commerce of the United States (through the general participation of its people and industry) and to the enhancement of the security of the nation.  The recent loss of Shuttle Columbia has only heightened the perception that we are adrift in space, with no long-term goals or direction. Death and risk are part of life and not to be feared, especially in the field of exploration, but for death to have meaning, the objectives of such exploration must be significant.  Great nations do great (and ambitious) things.  The Apollo project was one such example; a return to the Moon to learn how to live off-planet can be another.

(2) Human missions to Mars currently are too technically challenging and too expensive to be feasible national space goals within the next decade.

Although much attention is given to the idea of human missions to Mars as the next big goal in space, such a journey is at present beyond our technical and economic capabilities.  The large  amount of discretionary money needed for such a journey is simply not available in the federal budget nor would it be wisely spent on going to Mars in an Apollo-style "flags-and-footprints" program.  The principal justification of a manned Mars mission is scientific and such a rationale cannot sustain a large investment in the eyes of the taxpaying public.  Mars awaits exploration by people some time in the future, after we have learned how to live and work routinely in space and how to make use of the resources available on other worlds to break the costly ties to Earth-based rocket transport of materiel.

American government has a history of supporting long-term, big engineering projects, provided that such efforts contribute to goals related to national and economic security (e.g., the Panama Canal, the Apollo program). The nation needs a mission whose purpose relates to these important, enduring objectives. A return to the Moon is such a goal.  Indeed, it is a necessary goal and the only economically-justifiable goal at this time.

(3) Other possible destinations for people in space are perceived to be either too uninteresting (asteroids) or too arcane (telescopes in deep space) to enjoy "widespread" national support.

Among other possible space destinations for people are the Lagranian (L-) points (imaginary spots in space that move in sync with Earth, Moon, Sun or other objects) and the minor planets, better known as asteroids. The Lagranian points have many advantages for the staging of missions that go elsewhere, but the only thing they contain is what we put there.  In that sense, they are similar to low Earth orbit and significant activity at the L-points, without travel beyond them to more interesting destinations, would resemble another International Space Station put in a different location.  Asteroids have great potential for exploration and exploitation of resources and may eventually become an important destination as a class of objects.  However, the times required to reach asteroids can equal the months-long transit times for Mars missions, without the variety of activities that could be undertaken at the end of such a trip.  Thus, although specialized missions to these destinations can be imagined, they do not present a compelling return on investment nor the scientific or operational variety that other missions possess.

(4) The Moon is close, accessible with existing systems, and has resources that we can use to create a true, economical space-faring infrastructure

The Moon is a scientific and economic treasure trove, easily reachable with existing systems and infrastructure that can revolutionize our national strategic and economic posture in space.  The dark areas near the poles of the Moon contain significant amounts (at least 10 billion tons) of hydrogen, most probably in the form of water ice.  This ice can be mined to support human life on the Moon and in space and to make rocket propellant (liquid hydrogen and oxygen).  Moreover, we can return to the Moon using the existing infrastructure of Shuttle and Shuttle-derived launch systems and the ISS for only a modest increase in the space budget within the next five years.

The "mission" of this program is to go to the Moon to learn how to use off-planet resources to make space flight easier and cheaper in the future.  Rocket propellant made on the Moon will permit routine access to cislunar space by both people and machines, which is vital to the servicing and protection of national strategic assets and for the repair and refurbishing of commercial satellites.  The availability of cheap propellant in low Earth orbit would completely change the way engineers design spacecraft and the way companies and the government think of investing in space assets.  It would serve to dramatically reduce the cost of space infrastructure to both the government and to the private sector, thus spurring economic investment (and profit).

(5) The Moon is a scientific treasure house and a unique resource, on which important research, ranging from planetary science to astronomy and high-energy physics, can be conducted.

Generally considered a simple, primitive body, the Moon is actually a small planet of surprising complexity. Moreover, the period of its most active geological evolution, between 4 and 3 billion years ago, corresponds to a "missing chapter" of Earth history. The processes that work on the Moon - impact, volcanism, and tectonism (deformation of the crust) - are the same ones that affect all of the rocky bodies of the inner solar system, including the Earth.  Because the Moon has no atmosphere or running water, its ancient surface is preserved in nearly pristine form and its geological story can be read with clarity and understanding. Because the Moon is Earth's companion in space, it retains a record of the history of this corner of the Solar System, vital knowledge unavailable on any other planetary object.

Of all the scientific benefits of Apollo, appreciation of the importance of impact, or the collision of solid bodies, in planetary evolution must rank highest. Before we went to the Moon, we had to understand the physical and chemical effects of these collisions, events completely beyond the scale of human experience.  Of limited application at first, this new knowledge turned out to have profound consequences. We now believe that large-body collisions periodically wipe out species and families on Earth, most notably, the extinction of dinosaurs 65 million years ago. The telltale residue of such large body impacts in Earth's past is recognized because of knowledge we acquired about impact from the Moon. Additional knowledge still resides there; while the Earth's surface record has been largely erased by the dynamic processes of erosion and crustal recycling, the ancient lunar surface retains this impact history. When we return to the Moon, we will examine this record in detail and learn about its evolution as well as our own.

Because the Moon has no atmosphere and is a quiet, stable body, it is the premier place in space to observe the universe. Telescopes erected on the lunar surface will possess many advantages.  The Moon's level of seismic activity is orders of magnitude lower than that of Earth.  The lack of an atmosphere permits clear viewing, with no spectrally opaque windows to contend with; the entire electromagnetic spectrum is visible from the Moon's surface.  Its slow rotation (one lunar day is 708 hours long, about 28 terrestrial days) means that there are long times of darkness for observation.  Even during the lunar day, brighter sky objects are visible through the reflected surface glare.  The far side of the Moon is permanently shielded from the din of electromagnetic noise produced by our industrial civilization.  There are areas of perpetual darkness and sunlight near the poles of the Moon.  The dark regions are very cold, only a few tens of degrees above absolute zero and these natural "cold traps" can be used to passively cool infrared detectors.  Thus, telescopes installed near the lunar poles can both see entire celestial hemispheres all at once and with infrared detectors, cooled for "free," courtesy of the cold traps.

(6) Hydrogen, probably in the form of water ice, exists at the poles of the Moon that can be extracted and processed into rocket propellant and life-support consumables

The joint DoD-NASA Clementine mission was flown in 1994.  Designed to test sensors developed for the Strategic Defense Initiative (SDI), Clementine was an amazing success story.  This small spacecraft was designed, built, and flown within the short time span of 24 months for a total cost of about $150 M (FY 2003 dollars), including the launch vehicle.  Clementine made global maps of the mineral and elemental content of the Moon, mapped the shape and topography of its surface with laser altimetry, and gave us our first good look at the intriguing and unique polar regions of the Moon.  Clementine did not carry instruments specifically designed to look for water at the poles, but an ingenious improvisation used the spacecraft communications antenna to beam radio waves into the polar regions; radio echoes were observed using the Deep Space Network dishes.  Results indicated that material with reflection characteristics similar to ice are found in the permanently dark areas near the south pole.  This major discovery was subsequently confirmed by a different experiment flown on NASA's Lunar Prospector spacecraft four years later in 1998.

The Moon contains no internal water; all water is added to it over geological time by the impact of comets and water-bearing asteroids.  The dark areas near the poles are very cold, only a few degrees above absolute zero.  Thus, any water that gets into these polar "cold traps" cannot get out so over time, significant quantities accumulate.  Our current best estimate is that over 10 billion cubic meters of water exist at the lunar poles, an amount equal to the volume of Utah's Great Salt Lake - without the salt!  Although hydrogen and oxygen can be extracted directly from the lunar soil (solar wind hydrogen is implanted on the dust grains of the surface, allowing the production of propellant and water directly from the bone-dry dust), such processing is difficult and energy-expensive.  Polar water has the advantage of already being in a concentrated useful form, greatly simplifying scenarios for lunar return and habitation.  Broken down into hydrogen and oxygen, water is a vital substance both for human life support and rocket propellant.  Water from the lunar cold traps advances our space-faring infrastructure by creating our first space "filling station."

The poles of the Moon are useful from yet another resource perspective - the areas of permanent darkness are in proximity to areas of near-permanent sunlight.  Because the Moon's axis of rotation is nearly perpendicular to the plane of the ecliptic, the sun always appears on or near the horizon at the poles.  If you're in a hole, you never see the Sun; if you're on a peak, you always see it.  We have identified several areas near both the north and south poles of the Moon that offer near-constant sun illumination.  Moreover, such areas are in darkness for short periods, interrupting longer periods of illumination.  Thus, an outpost or establishment in these areas will have the advantage of being in sunlight for the generation of electrical power (via solar cells) and in a benign thermal environment (because the sun is always at grazing incidence); such a location never experiences the temperature extremes found on the lunar equator (from 100° to -150° C).  The poles of the Moon are inviting "oases" in near-Earth space.

(7) Current launch systems, infrastructure, and space hardware can be adapted to this mission and we can be back on the Moon within five to seven years for only a modest increase in existing space budgets.

America built the mighty Saturn V forty years ago to launch men and machines to the Moon in one fell swoop.  Indeed, this technical approach was so successful, it has dominated the thinking on lunar return for decades.  One feature of nearly all lunar return architectures of the past twenty years is the initial requirement to build or re-build the heavy lift launch capability of the Saturn V or its equivalent.  Parts of the Saturn V were literally hand-made, making it a very expensive spacecraft.  Development of any new launch vehicle is an enormously expensive proposition.  What is needed is an architecture that accomplishes the goal of lunar return with the least amount of new vehicle development possible.  Such a plan will allow us to concentrate our efforts and energies on the most important aspects of the mission - learning how to use the Moon's resources to support space flight.

One possible architecture for lunar return devised by the Office of Exploration at the Johnson Space Center has several advantages.  First, and most importantly, it uses the Space Shuttle (or an unmanned derivative of it), augmented by existing expendable boosters, to deliver the pieces of the lunar spacecraft to orbit.  Thus, from the start, we eliminate one of the biggest sources of cost from the equation, the requirement to develop a new heavy-lift launch vehicle.  This plan uses existing expendable launch vehicle (ELV) technology to deliver the cargo elements of the lunar return to low Earth orbit - lander, habitat, and transfer stage.  Assembled into a package in Earth orbit, these items are then transferred to a point about 4/5 of the way to the Moon, the Moon-Earth Lagranian point 1 (L1).  The L1 point orbits the Earth with the Moon such that it appears "motionless" to both bodies.  Its non-motion relative to Earth and Moon has the advantage of allowing us to wait for favorable alignments of these bodies and the Space Station in various phases of the mission.  Because there is no requirement for quick transit, cargo elements can take advantage of innovative technologies such as solar electric propulsion and weak stability boundaries between Earth, Sun, and Moon to make long, spiraling trips out to L1, thus requiring less propellant mass.  These unmanned cargo spacecraft can take several months to get to their destinations.  The habitat module can be landed on the Moon by remote control, activated, and await the arrival of its occupants from Earth.

The crew is launched separately on a Shuttle launch and uses a chemical stage and a quick transfer trajectory to reach the L1 depot in a few days.  The crew then transfers to the lunar lander/habitat, descends to the surface and conducts the surface mission.  As mentioned above, the preferred landing site is an area near one of the Moon's poles; the south pole is most attractive from the perspective of science and operations (see the attached "Shackleton Crater Expedition" proposal submitted to the committee by Dr. Stone).  The goal of our mission is to learn how to mine the resources of the Moon as we build up surface infrastructure to permit an ever-larger scale of operations.  Thus, each mission brings new components to the surface and the size and capability of the lunar outpost grows over time.  Most importantly, the use of lunar-derived propellants means that more than 80% of the spacecraft weight on return to Earth orbit need not be brought from Earth.  A properly designed mission will return to Earth not only with sufficient fuel to take the craft back to the Moon for another run, but also to provide a surplus for sale in low Earth orbit.  It is this act that creates the Earth-Moon economy and demonstrates a positive return on investment.

On return, the L1 depot provides a safe haven for the crew while they wait several days for the orbital plane of ISS to align itself with the return path of the crew vehicle.  Rather than directly entering the atmosphere as Apollo did, the crew return vehicle uses aerocapture to brake into Earth orbit, rendezvous with the ISS, and thus, it becomes available for use in the next lunar mission.

In addition to its technical advantages, this architecture offers important programmatic benefits.  It does not require the development of a new heavy lift launcher.  We conduct our lunar mission from the ISS and return to it afterwards, making the Station an essential component of humanity's movement into the Solar System.  The use of the L1 point as a staging depot allows us to wait for proper alignments of the Earth and Moon; the energy requirements to go nearly anywhere beyond this point are very low.  The use of newly developed, low-thrust propulsion (i.e., solar-electric) for cargo elements drives new technology development.  We will acquire new technical innovation as a by-product of the program, not as a critical requirement of the architecture.

The importance of using the Shuttle or Shuttle-derived launch vehicles and commercial launch assets in this architecture should not be underestimated.  Costs in space launch are almost completely dominated by the costs of people and infrastructure.  To create a new launch system requires new infrastructure, new people, new training.  Such costs can make up significant fractions of the total program.  By using existing systems, we can concentrate our resources on new equipment and technology, focused on the goal of finding, characterizing, processing, and using lunar resources as soon as possible.

(8) A return to the Moon gives the nation a challenging mission and creates capability for the future, by allowing us to routinely travel at will, with people, throughout the Earth-Moon system.
Implementation of this objective for our national space program would have the result of establishing a robust transportation infrastructure, capable of delivering people and machines throughout cislunar space.  Make no mistake - learning to use the resources of the Moon or any other planetary object will be a challenging technical task.  We must learn to use machines in remote, hostile environments, working under difficult conditions with ore bodies of small concentration.  The unique polar environment of the Moon, with its zones of near-permanent illumination and permanent darkness, provides its own challenges.  But for humanity to have a future, we must learn to use the materials available off-planet.  We are fortunate that the Moon offers us a nearby, "safe" laboratory to take our first steps in using space resources.  Initial blunders in mining tactics or feedstock processing are better practiced at a location three days from Earth than from one many months away.

A mission learning to use these lunar resources is scalable in both level of effort and the types of commodities to be produced.  We begin by using the resources that are the easiest to extract.  Thus, a logical first product is water derived from the lunar polar deposits.  Water is producible here regardless of the nature of the polar volatiles - ice of cometary origin is easily collected and purified, but even if the polar materials are composed of molecular hydrogen, this substance can be combined with oxygen extracted from rocks and soil (through a variety of processes) to make water.  Water is easily stored and used as a life-sustaining substance for people or broken down into its constituent hydrogen and oxygen for use of rocket propellant.

Although we currently possess enough information to plan a lunar return now, investment in a few  robotic precursors would be greatly beneficial.  We should map the polar deposits of the Moon from orbit using imaging radar to "see" the ice in the dark regions.  Such mapping could establish the details of the ice location and its thickness, purity, and physical state.  The next step should be to land small robotic probes to conduct in place chemical analyses of the material.  Although we expect water ice to dominate the deposit, cometary cores are made up of many different substances, including methane, ammonia, and organic molecules, all of which are potentially useful resources.  We need to inventory these species, determine their chemical and isotopic properties, and their physical nature and environment.  Just as the way for Apollo was paved by such missions as Ranger and Surveyor, a set of robotic precursor missions, conducted in parallel with the planning of the manned expeditions, can make subsequent human missions safer and more productive.

After the first robotic missions have documented the nature of the deposits, focused research efforts would be undertaken to develop the machinery needed to be transported to the lunar base as part of the manned expedition.  There, human-tended processes and principles will be established and validated, thus paving the way to commercialization of the mining, extraction and production of lunar hydrogen and oxygen.

(9) This new mission will create routine access to cislunar space for people and machines, which directly relates to important national economic and strategic goals.

By learning space survival skills close to home, we create new opportunities for exploration, utilization, and wealth creation.  Space will no longer be a hostile place that we tentatively visit for short periods; it becomes instead a permanent part of our world.  Achieving routine freedom of cislunar space makes America more secure (by enabling larger, cheaper, and routinely maintainable assets on orbit) and more prosperous (by opening an essentially limitless new frontier.)

As a nation, we rely on a variety of government assets in cislunar space, ranging from weather satellites to GPS systems to a wide variety of reconnaissance satellites.  In addition, commercial spacecraft continue to make up a multi-billion dollar market, providing telephone, Internet, radio and video services.  America has invested billions in this infrastructure.  Yet at the moment, we have no way to service, repair, refurbish or protect any of these spacecraft.  They are vulnerable to severe damage or permanent loss.  If we lose a satellite, it must be replaced.  From redesign though fabrication and launch, such replacement takes years and involves extraordinary investment in the design and fabrication so as to make them as reliable as possible.

We cannot now access these spacecraft because it is not feasible to maintain a man-tended servicing capability in Earth orbit - the costs of launching orbital transfer vehicles and propellant would be excessive (it costs around $10,000 to launch one pound to low Earth orbit).  Creating the ability to refuel in orbit, using propellant derived from the Moon, would revolutionize the way we view and use our national space infrastructure.  Satellites could be repaired, rather than abandoned.  Assets can be protected rather than written off.  Very large satellite complexes could be built and serviced over long periods, creating new capabilities and expanding bandwidth (the new commodity of the information society) for a wide variety of purposes.  And along the way, we will create opportunities and make discoveries.

A return to the Moon, with the purpose of learning to mine and use its resources, thus creates a new paradigm for space operations.  Space becomes a part of America's industrial world, not an exotic environment for arcane studies.  Such a mission ties our space program to its original roots in making us more secure and more prosperous.  But it also enables a broader series of scientific and exploratory opportunities.  If we can create a spacefaring infrastructure that can routinely access cislunar space, we have a system that can take us to the planets.

(10) The infrastructure created by a return to the Moon will allow us to travel to the planets in the future more safely and cost effectively.

This benefit comes in two forms.  First, developing and using lunar resources can enable flight throughout the Solar System by permitting the fueling the interplanetary craft with materiel already in orbit, saving the enormous costs of launch from Earth's surface.  Second, the processes and procedures that we learn on the Moon are lessons that will be applied to all future space operations.  To successfully mine the Moon, we must learn how to use machines and people in tandem, each taking advantage of the other's strengths.  The issue isn't "people or robots?" in space; it's "how can we best use people and robots in space?"  People bring the unique abilities of cognition and experience to exploration and discovery; robots possess extraordinary stamina, strength, and sensory abilities.  We can learn on the Moon how to best combine these two complementary skill mixes to maximize our exploratory and exploitation abilities.

Return to the Moon will allow us to regain operational experience on another world.  The activities on the Moon make future planetary missions less risky because we gain this valuable experience in an environment close to Earth, yet on a distinct and unique alien world.  Systems and procedures can be tested, vetted, revised and re-checked.  Exploring a planet is a difficult task to tackle green; learning to live and work on the Moon gives us a chance to crawl before we have to walk in planetary exploration and surface operations.

The establishment of the Earth-Moon economy may be best accomplished through an independently organized federal expedition along the lines of the Lewis and Clark expedition.  Dr. Stone, who is eminently qualified to lead such an expedition, has prepared the Shackleton Crater Expedition proposal (attached to this testimony) to elaborate upon this alternative organizational strategy.  One of the fundamental tenets of this approach is to take a business stance on cost control with the objective of demonstrating a positive return on investment.  Such an approach would take advantage of the best that NASA and other federal agencies have to offer, while streamlining the costs through a series of hard-nosed business approaches.

A lunar program has many benefits to society in general. America needs a challenging, vigorous space program. Such a program has served as an inspiration to the young for the last 50 years and it can still serve that function. It must present a mission that inspires and enriches. It must relate to important national needs yet push the boundaries of the possible. It must serve larger national concerns beyond scientific endeavors. A return to the Moon fulfills these goals. It is a technical challenge to the nation. It creates security for America by assuring access and control of our assets in cislunar space. It creates wealth and new markets by producing commodities of great commercial value. It stimulates and inspires the next generation by giving them the chance to travel and experience space flight for themselves.  A return to the Moon is the right destination for America.

Thank you for your attention.


Roger Angel, Testimony for Senate hearing on Lunar Exploration, November 6th 2003

Roger Angel
Steward Observatory, University of Arizona

Testimony for Senate hearing on Lunar Exploration, November 6th 2003

I am an astronomer at the University of Arizona, where big ground-based telescopes and their mirrors are made. We are now completing construction of the Large Binocular Telescope, which will become the single largest in the world.

In September this year I chaired a meeting sponsored by the National Academy of Science's Space Studies Board to look at future needs and technologies for large optics in space. We found broad interest in sizes beyond the 2.4 m Hubble and planned 6 m James Webb Space Telescopes, for astronomical research, for environmental studies and for defense. The different uses lead to different telescope configurations, wavelengths of operation (from ultraviolet to millimeter), and different optimum locations. But we found strong common interest across the agencies in developing technologies to make and control very big optical systems to exquisite, diffraction-limited quality and in the infrastructure to construct, deploy and service very large optical systems in space.  

For Earth imaging and defense, the optical systems need to be near Earth, and geosynchronous orbits are especially valuable. For astronomy, operation in low Earth orbit, like Hubble Space Telescope, has the huge, proven advantage of astronaut access, but has limits because of the constant cycling in and out of sunlight. The major limit is that deep infrared observations are not possible, because they require a cryogenically cooled telescope, permanently shaded from solar light and far from the heat radiated by the warm Earth. The recently launched 0.9 m SIRTF telescope and the Webb telescope are in such locations. 

Let me mention two different astronomical goals that would need even larger telescopes.  One is detection of warm, Earth-sized planets around nearby stars like the sun. We expect to find them with bigger telescopes, but have no idea if they will have life. But we could find out by analyzing their spectra. Another goal will be to see the light of the first stars that has been on its way towards us through most of time.  Our understanding is that the big bang created a uniform gas of just hydrogen and helium, and that after this cooled off the universe was completely dark and without form for hundreds of millions of years.  And then there was light.  Gravity had slowly pulled the gas together into lumps and then into to massive, brilliant stars, whose nuclear burning started to produce the elements like carbon and oxygen and iron from which the Earth and life are made. 

We know a lot about the big bang, because it was so bright we can easily see and analyze its brilliant light, now cooled off to become radio waves.  First seen from New Jersey, these were recently mapped out from Antarctica and by NASA's cryogenic WMAP spacecraft.  Today we can only speculate on the first stars, but their light will now be in the form of faint heat waves.  Given a very big, very cold telescope in space that stares for a year or more at the same spot, we could likely detect them and analyze their spectra.

What we need for a such a telescope is find a way to combine the capability for maintenance and improvement of HST with operation at a remote, permanently shaded operation.  Most thinking so far at NASA has focused on operation at the WMAP and proposed Webb location, in an orbit of the sun a million miles beyond Earth's (L2).  Servicing would likely involve ferrying a telescope (or part of it) to a nearer orbit, but still ¼ million miles away, for more convenient access.

An alternative location for a very large telescope would be the lunar south pole, in the Shackleton crater where the sun never shines and cryogenic temperatures prevail. This would be convenient for construction and maintainance if there were a Moon base at the pole. The Moon has no atmosphere, so light from the stars would have the same pristine quality as in free space.  Only the southern hemisphere would be observable, but this is not a major astronomical limitation.

The lunar south pole is a good choice for siting a lunar base, independent of any telescope.  The craters are believed to contain water ice, most valuable than gold for the base1.  Also, the crater rim has small areas of nearly eternal sunshine, simplifying problems of maintaining electric power and temperate living conditions2.  Furthermore, the adjacent South-Pole-Aitken basin is the oldest and deepest impact crater on the Moon, and has been flagged for study in the recent NRC study3.

Many technical, engineering and infrastructure issues remain to be explored. The Moon provides a platform on which to build big structures, but it also comes with gravity and weight, albeit at 1/6th of the Earth's value. Freely-orbiting telescopes avoid the need for bearings and drives.  Magnetic levitation on superconducting bearings might simplify the task of turning the telescope around during each month to track the stars.  We would need to make sure the telescope optics are not compromised by vibrations or dust and condensed gas from the base.       

Gravity can be turned to an advantage for the kind of telescope we need to look back to the first stars.  These will be all over the sky, and a good place to look is straight overhead. From the Moon's pole the infrared sky is darkest overhead, and we can look at the same unchanging patch of sky for the years  needed to study the extremely faint first stars. A specialized telescope for this work doesn't have to move.  Very high resolution images could be made with multiple such telescopes laid out as an interferometer, with no moving parts. We may even be able to use a trick to make a telescope mirror looking straight up by spinning a thin layer of reflecting liquid in a big dish. A 6-m diameter telescope of very high quality has been built like this very inexpensively in Canada4. Bigger ones won't work on the Earth because the spinning makes a wind that ruffles the surface. But with no wind or air on the Moon, a 20 m or larger mirror might be made this way. A cryogenic liquid with evaporated gold coating would be used.  A fixed telescope would not satisfy many astronomical goals, which need access over a good part of the sky.  For example, the few nearby stars where we can hope to study Earth-like planets are randomly distributed all over the sky.  But a liquid telescope at a manned base could undertake one of the challenging observations we have for big telescopes. Experience developed in this way at the base might then show that a fully-steerable big telescope would be practical on the Moon.    

More details of the liquid mirror telescope and its scientific potential are give in the attached white paper.  

1. Vondrak, R. R. and Crider, D. H.  Ice at the Lunar Poles.  American Scientist (2003)

2. Bussey, D. B. J., Robinson, M. S., Spudis, P. D.  Illumination Conditions at the Lunar Poles  30th Annual Lunar and Planetary Science Conference, Houston (1999)

4. Cabanac, R. A., Hickson, P. and de Lapparent, V.  The Large Zenith Telescope Survey: A Deep Survey Using a 6-m Liquid Mirror Telescope in A New Era in Cosmology, eds Metcalfe, N. and Shanks, T.  ASP Conference Proceedings 283. p 129  (2002)            

3. NRC  New Frontiers in the Solar System: An Integrated Exploration Strategy.  Space Studies Board  (2002)

5. Page, T and Carruthers, G. R. Distribution of hot stars and hydrogen in the Large Magellanic Cloud.  Ap. J. 248, 906-924 (1981)


CNN, 6 November 2003

By Kate Tobin and Richard Stenger
(CNN) -- The massive solar flare that erupted from the sun this week has been classified as the largest in three decades of monitoring, the National Oceanic and Atmospheric Administration's Space Environment Center said Thursday.

The previous record holder occurred on April 2, 2001. An active region of sunspots on the solar face has spawned a number of powerful flares over the last two weeks, including the most powerful one on Tuesday and third largest salvo on record on October 28.

"Just as solar scientists were ready to start breathing normally again, active region 10486 blasted off yet another mega-flare," Paal Brekke of the European Space Agency said of the November 4th flare. "This one saturated the X-ray detectors on the NOAA's GOES satellites that monitor the sun."

Solar flares often herald coronal mass ejections, or CMEs, clouds of electrified gas called plasma that explode from the sun and wash out over the solar system.

If the CME hits Earth, the charged particles can interact with the planet's electromagnetic field and result in a geomagnetic storm. In extreme cases, the storms can interfere with satellite operations or overload power grids on Earth.

They can also produce spectacular displays of the northern and southern lights. The coronal mass ejection coupled with Tuesday's flare was not headed in our direction, so it did not have a strong impact on Earth.

Space weather forecasters say this recent string of strong solar flares is not consistent with normal solar behavior. The sun, which follows an 11-year activity cycle, had been mostly quieting down since the last peak in 2000.

Copyright 2003, CNN

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CCNet 101/2003 - 7 November 2003

IN SCIENCE, as in most fields of human endeavour, fashion plays a role.
Two decades ago, evidence was discovered that the dinosaurs (and a great
many other, less well-known, creatures) were exterminated by a collision
between the Earth and an extra-terrestrial rock.... Alternative explanations
for mass extinctions, such as the huge volcanic eruptions that often seem
to coincide with them, have fallen out of fashion. Fashion, however, is
fickle, and those other explanations are once again jostling on the catwalk
with the impact theory. The evidence for a single huge impact which wiped out
the dinosaurs is itself under attack.
     --The Economist, 6 November 2003

    The Economist, 6 November 2003

    Adrian Jones and David Price (UCL)

    B.A. Ivanov and H.J. Melosh

    Andrew Glikson
    Dallas H. Abbott and Ann E. Isleyb


The Economist, 6 November 2003

IN SCIENCE, as in most fields of human endeavour, fashion plays a role. Two decades ago, evidence was discovered that the dinosaurs (and a great many other, less well-known, creatures) were exterminated by a collision between the Earth and an extra-terrestrial rock. The evidence came in the form of a layer of clay rich in iridium that has been identified in sites all around the world, and appears to be the result of such a collision. One decade ago, a crater that seemed to be the same age as this layer was identified in southern Mexico. Since then, it has become fashionable to look for evidence of impacts at the time of the other four so-called mass extinctions that the record suggests have happened since fossils became abundant 545m years ago. Conversely, alternative explanations for mass extinctions, such as the huge volcanic eruptions that often seem to coincide with them, have fallen out of fashion.

Fashion, however, is fickle, and those other explanations are once again jostling on the catwalk with the impact theory. Some were aired at the annual meeting of the Geological Society of America (GSA) held in Seattle during the first few days of November. Meanwhile, the evidence for a single huge impact which wiped out the dinosaurs is itself under attack. Those sniping at it are not-at least not yet-arguing that the impact theory is completely wrong. But they are arguing that the Mexican crater is not part of the story because, they say, it was made some 300,000 years before the dinosaurs disappeared.

Sudden impact

The chief heretics are Gerta Keller of Princeton University in America, Thierry Adatte of the University of Neuchâtel in Switzerland, and Wolfgang Stinnesbeck of the University of Karlsruhe in Germany. In April, they announced preliminary data to support their dissent at a conference in Nice. They have now published them in the Journal of the Geological Society (the society in question being the British, rather than the American one).

The moment most people were persuaded that the dinosaurs were killed by an impact was when the crater in Mexico was shown to have been created 65m years ago, at the end of the Cretaceous period. This was when the iridium layer was formed (many extra-terrestrial rocks are far richer in iridium than those found on Earth, so a large impact that scattered the iridium seemed a reasonable conclusion to draw), and when the dinosaurs disappeared. But dating things as old as this, which is done by studying the products of radioactive decay, is not a precise science. An error of 300,000 years is not out of the question. This is where Dr Keller and her collaborators come in. They have convinced themselves that, wherever the iridium came from, it was not ejected by the Mexican impact.

The environment

Their evidence comes from the rocks of the Gulf of Mexico and the Caribbean that surround the crater. These contain small glass globules. No one disputes that these globules were formed from stuff melted and thrown into the air by the impact, because their chemical composition matches rock from the crater itself. Above the globules are several metres of sandstone, shale and limestone. Then comes the iridium.

The conventional explanation for this arrangement is that the glass fell to Earth first, then giant waves caused by the impact covered them with sediment, then iridium-containing dust settled out of the atmosphere over the course of a few weeks and formed the clay.

Dr Keller, however, contends that the sandstone, shale and limestone layers were deposited over a long period of time. Her evidence is that many of these layers contain animal burrows that seem to start at the surface of the layer, suggesting that the layer in question had been buried subsequently. She has also found several layers of globules. She is not suggesting that these came from different impacts (they are all chemically similar to one another), but rather that the sediments have been "reworked", perhaps by subsequent mudslides. That, again, would have taken time.

Most tellingly, she says that rock cores taken recently from the crater itself show a band of sediment above the impact that contains fossils of tiny creatures that became extinct only at the end of the Cretaceous. This band also contains several layers of a mineral called glauconite, each of which would have taken tens of thousands of years to form.

Putting all this together, she suggests the Mexican impact happened 300,000 years before the end of the Cretaceous. The iridium, and the end of the dinosaurs, she believes, were caused by another impact whose crater has yet to be located.

Naturally, not everyone agrees with this interpretation of the data. Jan Smit, of the Free University in Amsterdam, is particularly critical. It was he who first came up with the giant-wave explanation for the layers of sediment between the glass globules and the iridium.

According to Dr Smit, the multiple layers were the result of waves from the impact sloshing around in the primitive Gulf of Mexico and passing over individual sites several times. And the microfossils in the sediment over the crater are either misinterpretations of material that has recrystallised over time, or were washed in from nearby rocks just after the crater was formed. He points out that rocks from contemporary swamps in North America show little separation between the glass globules and the iridium. It is also unlikely that two impacts as big as the one that caused the Mexican crater and the one that spread iridium around the world would occur within 300,000 years of each other. But, of course, it is not impossible.

It's a gas

So what killed the dinosaurs is still disputed by some. But a question which is just as intriguing is: what brought them to power in the first place? The answer may have something to do with another mass extinction, this time some 202m years ago at the end of the Triassic period. The Triassic was the first age of reptiles. Dinosaurs existed, but were a minor part of the fauna. However, when the other reptiles died out, the dinosaurs went sailing on. Peter Ward, of the University of Washington, in Seattle, told the GSA that he thinks he knows what caused the extinction, and that it explains the dinosaurs' success.

Dr Ward's explanation draws on work by Robert Berner, at Yale. Four years ago Dr Berner put together all the available evidence and estimated how the level of oxygen has changed over the past 600m years. His model suggests it peaked at around 35% of the atmosphere some 300m years ago, then more than halved over the course of about 75m years. It remained low for 50m years, then picked up and has hung around its current level (21%) ever since. This meant that there was a long period when the air would have been about as breathable as that now found at the top of a high mountain.

This, in itself, would not be enough to cause a mass extinction, but it might set the stage. Dr Ward's thesis is that the volcanic eruptions which marked the end of the Triassic filled the atmosphere with greenhouse gases such as carbon dioxide. That would cause the temperature to rise, putting further stress on animals, and would favour those with efficient breathing mechanisms.

As it happens, dinosaurs appear to have had such a mechanism. Like the birds which are their descendants, many of them had hollow bones. Like those of birds, these hollows probably contained air sacs, and that would have allowed dinosaurs to have a bird-like breathing mechanism in which the air passes right through the lungs twice (once on the way in and once on the way out). This is much more efficient than drawing air in and then leaving it to hang around before expelling it, and Dr Ward reckons it gave the dinosaurs an edge that allowed them to survive conditions at the end of the Triassic, and subsequently prosper.

Dr Ward thinks that a similar mechanism of little oxygen and greenhouse warming was also responsible for the biggest mass extinction of all, that at the end of the Permian, some 251m years ago, when 95% of species known from fossils died out. However, Lee Kump, a geologist at Pennsylvania State University, suspects there was more to it than that. Besides being stifled, he reckons, Permian life may have been poisoned.

The poison, Dr Kump suggested to the GSA meeting, was hydrogen sulphide. Like the end of the Triassic (and, indeed, the end of the Cretaceous) the end of the Permian was a time of huge vulcanism. As conditions deteriorated, and oxygen became scarcer and scarcer, undecayed organic matter would have accumulated in the oceans, encouraging so-called anaerobic bacteria, which can live only in oxygen-free conditions. Many of these bacteria generate hydrogen sulphide as a waste product. Dr Kump's hypothesis is that at an inconvenient moment a lot of this gas "burped" to the surface.

The only problem with Dr Kump's hypothesis is that he has no actual evidence for it. But he hopes to gather some soon, from rocks in Japan. And if he does, you can bet that yet another theory will come oozing down the catwalk to sneer at it.

Copyright © The Economist Newspaper Limited 2003. All rights reserved.


Adrian Jones <>

Dear Benny,

A recent paper by Jay Melosh and Boris Ivanov (Geology 31, 869-872) emphatically attempts
to deny a causal link between large impacts and volcanism, although within the body of
the text, they accept that impact volcanism probably operated during the early Earth history.
This is certainly the opinion of Richard Greive, who recently described 'the gigantic melt
pools' he envisaged which would have arrived perhaps monthly during the late heavy bombardment,
and emphasised the complete absence at that time of anything resembling a large crater, in
stark contrast to what is now seen on, for example, the Moon. Impact models must now address
more closely the thermal and compositional complexity appropriate for terrestrial targets
whose thermal structure is in fact relatively precisely known.  Hotter rocks melt at lower
shock pressures, and the decompression melting behaviour of mantle rocks is well understood. 
We agree with Melosh and Ivanov that large meteorite impacts trigger volcanism in hot rocks,
but we disagree over the details, and we are unconvinced that this can be dismissed for the
Phanerozoic. Melosh and Ivanov reduce the signifcance of the process by alluding to the
unlikelihood of a large impact coexisting with a pre-existing mantle hotspot.  We suggest
instead that a range of crater sizes (diameters and depths) would produce different melting
responses according to, for example, age of oceanic lithosphere related to active spreading
ridges. Thus  as recently suggested by Cofin and Ingle (AGU, EUG Nice Meeting April 2003),
the Ontong Java Oceanic Plateau does not seem to be explainable by the plume hypothesis,
but rather they advocate an impact origin.  This would have involved impacting into oceanic
lithosphere < 20 Ma old, where high geothermal gradients and near-surface mantle is to
be expected.

The potential significance of impact-generated mantle hot spots, magmatism and impact
plumes is obvious, and we would like to direct readers to our IMPACTS piece on the excellent
plumes website maintained by Gillian Foulger (  The fundamental
relationship between impact-generated melt volume (both from kinetic energy and gravitational
energy via decompression) and thermal structure is reminiscent of the komatiite conundrum.
Komatiites were once thought to be confined to formation during the early Earth when mantle
temperatures were hotter.  We now know that much younger komatiites exist.  We maintain that
large impacts should still be considered a favourable mechanism for generating enormous
quantities of melt similar in volume to large igneous provinces, and such a hypothesis is testable. 

Adrian Jones and David Price (UCL)


Geology: Vol. 31, No. 10, pp. 869-872.

Impacts do not initiate volcanic eruptions: Eruptions close to the crater
B.A. Ivanov
Institute of the Dynamics of the Geospheres, 38-6 Leninsky Prospect, Moscow 11797, Russia

H.J. Melosh
Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA

Manuscript Received by the Society 26 March 2003
Revised Manuscript Received 18 June 2003
Manuscript Accepted 23 June 2003


Many papers on meteorite impact suggest that large impacts can induce volcanic eruptions
through decompression melting of the underlying rocks. We perform numerical simulations of
the impact of an asteroid with a diameter of 20 km striking at 15 km·s-1 into a target with
a near-surface temperature gradient of 13 K·km-1 ("cold" case) or 30 K·km-1 ("hot" case).
The impact creates a 250-300-km-diameter crater with 10,000 km3 of impact melt. However,
the crater collapses almost flat, and the pressure field returns almost to the initial
lithostat. Even an impact this large cannot raise mantle material above the peridotite solidus
by decompression. Statistical considerations also suggest that impacts cannot be the common
initiator of large igneous provinces any time in post-heavy bombardment Earth history.
Keywords: impact, volcanism, decompression melting, large igneous provinces, impact volcanism.

© Copyright by Geological Society of America 2003


Earth and Planetary Science Letters, 30 October 2003!&_cdi=5801&view=c&_acct=C000043031&_version=1&_urlVersion=0&_userid=777686&md5=a7a11d0c1bc81c480b76697f2188b387
Volume 215, Issues 3-4 , 30 October 2003, Pages 425-427
Comment on "Extraterrestrial influences on mantle plume activity" by D.H. Abbott and A.E. Isley
[Earth Planet. Sci. Lett. 205 (2002) 53-62]

Andrew Glikson, 
Research School of Earth Science, Australian National University, Canberra, ACT 0200, Australia
Received 23 January 2003;  accepted 13 August 2003. ; Available online 18 September 2003.

Abbott and Isley [1] postulate cause-effect relations between large asteroid impacts and enhanced activity in mantle plumes through Earth history using wide-bin/interval time series analysis of age records of impact structures larger than 10 km in diameter, projections from Ar-Ar ages of lunar impact spherules, and ages of mafic-ultramafic igneous units. A search for potential links between large asteroid impacts and terrestrial volcanic events is justified by: (A) the post-3.8 Ga asteroid impact incidence deduced from lunar records, from well-preserved Proterozoic and Phanerozoic basins and from present-day astronomical observations in the order of 4-6×10-15 km-2 yr-1 for craters with Dc20 km [2, 3 and 4], (B) geochemical and isotopic evidence for the extent of oceanic crust >70% of the Earth surface through geological history [5], and (C) expected impact triggering of adiabatic melting and volcanic activity in thin oceanic crustal regions underlain by shallow asthenosphere [6 and 7].

Precise U-Pb zircon and baddeleyite isotopic age methods are capable of defining narrow age constraints of impact and magmatic events, with errors as small as ±0.05 Myr [8]. Should a statistically significant number of precise isotopic ages of large impact and igneous events coincide within isotopic age dating errors, the possibility of cause-effect connections may be supported, if not proved. A potential example is the temporal proximity of the K-T Chicxulub impact (64.98±0.05 Ma [8]) and peak Deccan volcanism (Ar-Ar age 66.4±1.9 Ma) located stratigraphically above arenite containing shocked quartz grains containing planar deformation features [9].

Abbott and Isley's [1] approach constitutes the reverse of precise age correlations, in that their statistical time series analysis involves widening (smoothing) of age dating errors to time bins/intervals as large as 30 Myr and 45 Myr, i.e. widening of isotopically defined age errors by two to three orders of magnitude. This results in correlation of impact and volcanic events with apparent confidence levels as high as 97%, which the authors [1] appear to regard as confirmation of cause-effect relations and of impact-enhanced mantle plume activity. However, that impact and mafic/ultramafic igneous events fall within time intervals in the order of 30 and 45 Myr in no way implies a cause-effect relationship, which is contradicted by the much narrower age constraints of each of these events. A temporal proximity within age limits, cf. Dales-Kuruman mega-impact (2.479±3 Ma [11]) and the Great Dyke (2461±16 Ma), does not necessarily prove a genetic relation, let alone the fit of the Vredefort impact (2023±4 Ma) and the Bushveld complex (2061±27 Ma) within a 45 Myr wide bin.

Applying yet wider age intervals/bins, the authors suggest "Using 250-Ma intervals, there are four large-scale peaks in plume activity over the last 3.8 Ga that are directly correlated with large-scale peaks in impact intensity" ([1], p. 60). The documented concentration of large impact fallout units and impact structures about 3.47, 3.24-3.117, 2.63-2.479, 1.85, 0.59, 0.47, 0.354, 0.21-0.22, 0.142, 0.120-128, 0.073, 0.065 and 0.035 Ga [8], which forms no more than 1.6% of the expected impact incidence for craters larger than 100 km [4], is hardly consistent with this assertion.

Abbott and Isley ([1], p. 55) suggest "This result implies that our technique of assembling impact data for the Earth has correctly identified most of the major impact events on the Earth." The pre-800 Ma impact record documented to date includes three impact structures (Vredefort, 2023±4 Ma; Sudbury, 1850±3 Ma; Suavjarvi, ~2400 Ma) [8] and six impact fallout units (Warrawoona and Onverwacht Groups ~3460 Ma; base Fig Tree Group cluster ~3240-3117 Ma; top Jeerinah Formation, Pilbara ~2630 Ma; Wittenoom Formation and Carawine Dolomite and Monteville Formation ~2560 Ma; Dales Gorge Member of the Brockman Iron Formation ~2490 Ma; ~2130-1848 Ma Ketilidian province, south Greenland [10, 11 and 12]). The total of nine identified impacts for the 3.8-0.8 Ga interval constitutes 0.1% of the estimated impact incidence of ~8000 asteroids >1 km in diameter, or 2.5% of the estimated impact incidence of ~350 asteroids >10 km in diameter, during this 3×109 years long time span. The overall preservation rate of craters larger than 18 km is estimated as about 0.38%, or 1.3% for craters larger than 100 km (six known continental impacts) [4]. The authors' ( [1], p. 55) claim of having identified "most of the major impact events on the Earth" is therefore surprising.

The authors [1] remark on "prominent lulls in impact activity during the Mesoproterozoic and at about 2.4 Ga". Quite apart from the observation of the 2.479 Ga Dales Gorge DS4 major impact fallout unit [11] and of the Mesoproterozoic 1.85 Ga Sudbury impact [8], the Precambrian impact database known to date, namely nine impacts, is hardly adequate for the definition of impact lulls.

Attempted correlations between the records of extraterrestrial impacts and mafic/ultramafic magmatic events suffer from severe database imbalance. Datasets for volcanic, hypabyssal and plutonic events include many hundreds of relatively accurate (errors less than ±5 Myr) isotopic ages. By contrast the impact dataset includes 33 relatively accurate isotopic ages (errors less than ±5 Myr) for structures with diameters >10 km and 10 such ages for structures of diameters >50 km [8]. Assuming that the structural and magmatic consequences are positively related to the size of impact, the database for accurate >50 km large impact structures is thus at least two orders of magnitude smaller than the database for accurate isotopic ages of mafic and ultramafic terrestrial igneous events.

Abbott and Isley ([1], p. 55) use Culler et al.'s [13] lunar Ar-Ar impact spherule age data with errors <150 Myr, which exceed precise U-Pb zircon dating errors by two to three orders of magnitude. Broad comparisons between the lunar Ar-Ar spherule age peaks and terrestrial impact episodes outline a number of potential correlations, including: (1) a lunar impact peak at ~3.18 Ga and the Fig Tree Group (Barberton, east Transvaal) impact cluster at 3.24-3.117 Ga [4]; (2) a possible lunar peak at 3.47 Ga correlated with the Warrawoona/Onverwacht ~3.47 Ga impacts [10]; (3) a possible lunar peak at 355 Ma correlated with the late Devonian 356 Ma impact cluster [4]. However, the significance of such correlations is severely constrained by the very small lunar regolith sample studied (~1 g) and the large age errors. The general concentration of lunar spherule Ar-Ar ages within pre-3.0 Ga and post-0.4 Ga intervals [13] may reflect the combination of volumetric dominance of early Archaean impact products and the concentration of Phanerozoic impact products toward the top of the regolith profile.

Tests of potential connections between large impacts and crustal magmatic and tectonic events [17] require further accurate dating of known, as well as discovery of yet unknown, impact events. At the present state of knowledge candidates for such relations may include: (1) correlation between the K-T boundary impact cluster (Chicxulub, 64.98±0.05 Ma; Boltysh, 65.17±0.54 Ma) [8], Deccan peak volcanism and the Carlsbad Ridge split [14, 15 and 16]; (2) potential relations between the late Triassic impact cluster (Manicouagan, 214±1 Ma; Rochechouart, 214±8 Ma) [8] and the onset of the mid- to north-Atlantic continental split and associated volcanic activity [18]; and (3) potential relations between the late Jurassic impact cluster (Morokweng, 145±0.8 Ma; Mjolnir, 142±2.6 Ma; Gosses Bluff, 142.5±0.8 [8]) and volcanism associated with the South Atlantic and Indian Ocean continental split.

The bulk of documented impact structures is located on continental crust. To date no correlations are known between the ages of these impacts and continental mafic dyke swarms, with the possible exception of the K-T Deccan traps. Little is known about the temporal and spatial distribution of oceanic impact structures [4], the more likely candidates for triggering adiabatic melting in thin near-mid-ocean ridge crustal domains. The methodology of testing potential relations between large extraterrestrial impacts, tectonic and igneous events depends critically on correlation of precise isotopic ages within age error limits.[BOYLE]

1. D.H. Abbott and I.S. Isley, Extraterrestrial influences on mantle plume activity. Earth Planet. Sci. Lett. 205 (2002), pp. 53-62. SummaryPlus | Full Text + Links | PDF (270 K)

2. R.A.F. Grieve, E.M. Shoemaker, The record of past impacts on Earth, in: T. Gehrels (Ed.), Hazards Due to Comets and Asteroids, The University of Arizona Press, Tucson, AZ, 1994, pp. 417-462.

3. E.M. Shoemaker and C.S. Shoemaker, The Proterozoic impact record of Australia. Aust. Geol. Surv. Org. J. 16 (1996), pp. 379-398. Abstract-GEOBASE   | $Order Document

4. A.Y. Glikson, The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2±0.1 Ga bombardment of the Earth-Moon system. J. Geodyn. 32 (2001), pp. 205-229. SummaryPlus | Full Text + Links | PDF (2481 K)

5. M.T. McCulloch and V.C. Bennett, Progressive growth of the Earth's continental crust and depleted mantle: geochemical constraints. Geochim. Cosmochim. Acta 58 (1996), pp. 4717-4738.

6. D.H. Green, Archaean greenstone belts may include terrestrial equivalents of lunar maria?. Earth Planet. Sci. Lett. 15 (1972), pp. 263-270. Abstract | Abstract + References | PDF (652 K)

7. D.H. Green, Petrogenesis of Archaean ultramafic magmas and implications for Archaean tectonics, in: A. Kroner (Ed.), Precambrian Plate Tectonics, Elsevier, Amsterdam, 1981, pp. 469-489.

8. Geological Survey of Canada and University of New Brunswick impact crater database:

9. A.R. Basu, S. Chatterjee and D. Rudra, Shock metamorphism in quartz grains at the base of the Deccan Traps: Evidence for impact-triggered flood basalt volcanism at the Cretaceous-Tertiary boundary. EOS Trans. AGU 69 (1985), p. 1487.

10. G.R. Byerly, D.R. Lowe, J.L. Woden and X.-g. Xie, A meteorite impact layer 3470 Ma from the Pilbara and Kaapvaal Cratons. Science 297 (2002), pp. 1325-1327. Abstract-Elsevier BIOBASE | Abstract-MEDLINE | Abstract-EMBASE | Abstract-GEOBASE | Abstract-INSPEC   | $Order Document | Full Text via CrossRef

11. B.M. Simonson and S.W. Hassler, Revised correlations in the early Precambrian Hamersley Basin based on a horizon of resedimented impact spherules. Aust. J. Earth Sci. 44 (1997), pp. 37-48. Abstract-GEOBASE   | $Order Document

12. B. Chadwick, P. Claeys and B.M. Simonson, New evidence for a large Palaeo-proterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, South Greenland. J. Geol. Soc. London 158 (2001), pp. 331-340. Abstract-GEOBASE   | $Order Document

13. T.S. Culler, T.A. Becker, R.A. Muller and P.R. Renne, Lunar impact history from 40Ar/39Ar dating of glass spherules. Science 287 (2000), pp. 1785-1788. Abstract-EMBASE | Abstract-INSPEC | Abstract-Elsevier BIOBASE | Abstract-GEOBASE   | $Order Document | Full Text via CrossRef

14. A.D. Alt, J.W. Sears and D.W. Hyndman, Terrestrial maria: The origins of large basalt plateaus hotspot tracks and spreading ridges. J. Geol. 96 (1988), pp. 647-662.

15. S. Chatterjee and D.K. Rudra, KT events in India: Impact, rifting, volcanism and dinosaur extinction. Mem. Qld. Mus. 39 (1996), pp. 489-532. Abstract-GEOBASE   | $Order Document

16. V.R. Oberbeck, J.R. Marshall and H. Aggarval, Impacts, tillites and the breakdown of Gondwanaland. J. Geol. 101 (1992), pp. 1-19.

17. R.B. Stothers and M. Rampino, Periodicity inflood basalts mass extinction and impacts: a statistical view and a model. Geol. Soc. Am. Spec. Pap. 247 (1990), pp. 9-18.

18. V. Courtillot, C. Jaupart, I. Manughetti, P. Tapponnier and J. Besse, On causal links between flood basalts and continental breakup. Earth Planet. Sci. Lett. 166 (1999), pp. 177-196.
Corresponding author. Tel./Fax: +61-2-6296-3853

Copyright © 2003 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters , 30 October 2003!&_cdi=5801&view=c&_acct=C000043031&_version=1&_urlVersion=0&_userid=777686&md5=186dfc091944dd7fa0e447234cf01d85

Volume 215, Issues 3-4 , 30 October 2003, Pages 429-432
Reply to Comment on `Extraterrestrial influences on mantle plume activity' by Andrew Glikson

Dallas H. Abbott, , a and Ann E. Isleyb
a Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA
b State University of New York at Oswego, Oswego, NY 13126, USA
Received 27 June 2003;  accepted 13 August 2003. ; Available online 18 September 2003.

We welcome Dr. Glikson's comments because they provide us with the opportunity to address certain common misunderstandings about the geological record with respect to plumes and impacts. There are some unstated assumptions in Glikson's analysis of our work that introduce flaws into his line of reasoning. Because these assumptions appear to be widely shared, it is useful to discuss them explicitly.

Implicit in Dr. Glikson's analysis is the assumption that the overall abundance of plume activity through geological time is indistinguishable from what we would expect based on the thermal history of the Earth. The ultimate driving force for mantle convection is internal heat production due to radioactive decay of long-lived isotopes in the mantle and core of the Earth. Previous workers have estimated that between 6 and 42% of the internal heat production of the Earth goes into the production of mantle plumes [1]. Over geologically long periods, e.g., 50-200 million years (roughly one Wilson cycle), the internal heat production of the Earth is expected to be at a steady state. Thus, when averaged over these intervals, the number of large plumes per unit time would be expected to diminish in accordance with the decline in the internal heat production of the Earth. The predicted abundance of plume activity per unit time varies with the particular thermal model used [2], but overall these models all predict that plume activity on the early Earth was greater than in the Phanerozoic and that there has been a gradual, smooth decline in plume activity up to the present time ( Fig. 1A).

Fig. 1. Histograms of three different data sets binned at 200 million years intervals. Values are plotted as percentage of area under the curve versus time in millions of years. A: Expected plume number over time, assuming that plume activity is driven only by the slow decline in the internal heat production of the Earth over geological time. Data are from the intermediate thermal model of [2]. B: Observed plume numbers over time. C: Observed impacts over time. Data sets for B and C are from [3 and 18].

However, this is not what we observe. Thus, Dr. Glikson's first implicit assumption is not supported by the actual data, which do not show a smooth decline in plume activity over the history of the Earth. Instead, there are periodic bursts and lulls in plume activity that closely mirror the bursts and lulls in impact activity (Fig. 1). Even with the limited data available, it is clear that the record of mantle plume activity follows the record of impact activity much more closely than it follows any model of the internal heat production of the Earth.

Glikson also implicitly assumes that a strengthening of a mantle plume in response to an impact would occur in a geologically short period of a million years or less. This assumption is correct for two of the three mechanisms for strengthening existing mantle plumes that we proposed in our paper: e.g., the formation of new cracks and de-stressing of the crust [3]. However, the third mechanism for strengthening mantle plumes, the production of microdikes at the core-mantle boundary, has an unknown time lag. Depending upon the type of convection model (Newtonian or non-Newtonian), modelers find that it takes a plume between a few million years to 50 million years to rise from the core-mantle boundary to the Earth's surface [4, 5 and 6]. The rise time of a plume will also vary depending upon the nature of the plume conduit. Therefore, there could be significant and highly variable time lags between impact events and the resultant strengthening of mantle plumes. The best way to test if plumes are strengthened by impacts is to look at data that have been smoothed with a relatively large time window, such as in the method we used where our interval was 30-45 million years.

Glikson is justifiably concerned that the terrestrial record of impact cratering is incomplete [7]. He infers that only 2.5% of all impacts by extraterrestrial bodies with diameters >10 km have been identified. In particular, he states that the Precambrian is poorly represented by terrestrial data, with only two well-dated craters (Vredefort and Sudbury) and a small number of terrestrial spherule layers. He questions whether the current lunar impact record [8] can be used as a proxy for the terrestrial impact record. He notes that only a small quantity of lunar material has been studied and that some of the spherule ages have large errors (±237 Myr). Finally, Glikson suggests that the statistical correlations observed between our data sets (which were as high as 97%) are artifacts that result from heavy-handed smoothing.

Indisputably, plate tectonics and other Earth surface processes have obscured evidence of many terrestrial impacts. For our analyses, we tackled this problem by splicing the records of the ages of terrestrial impact craters, terrestrial and lunar spherules, and terrestrial impact breccias. In other words, we combined all of the impact data available from both the Earth and the Moon. We obtained a time-series record of terrestrial impacts that is as robust as is currently possible to derive from available data. In our paper, we explicitly stated that there is only one time in Earth history for which the data support a direct, cause-and-effect relationship between a large impact and a consequent strengthening of a mantle plume. That is the K/T boundary, when strengthening of the already-active Deccan plume immediately followed the impact at Chicxulub. In all other cases, the correlation in time between plumes and impacts can only rely on smoothed data. The overall paucity of data on the abundance and ages of plumes and impacts does not allow any other approach. In fact, some aspects of the problem require that we use smoothed data.

The Precambrian is indeed poorly represented. However, the Vredefort (2023±4 Ma) and Sudbury (1850±3 Ma) craters are the two largest craters known on Earth. The poorly-dated Ketilidian spherule layer, 10 times thicker than any distal ejecta known from the Cretaceous-Tertiary impact, may have formed as a result of either the Vredefort or Sudbury event [9]. Some (~10) other Precambrian spherule layers are 10-100 times thicker than any of their Phanerozoic counterparts [10]. One then must infer that although the Precambrian record is poorly recorded, most (if not all) of the known events exceeded the magnitude of any Phanerozoic impacts.

Glikson [11] estimates that ca. 20-80 impacts in the past 3.8 Ga have left craters larger than 250 km diameter (extrapolating from his fig. 1). Assuming that all known terrestrial Precambrian impact events were substantially more significant than the Chicxulub impact, then based on Glikson's estimates, between 15 and 60% of all major impacts are captured in the data set we analyzed. Furthermore, as Glikson points out [7] and by analogy with the Shoemaker-Levy impacts on Jupiter [12], it is quite likely that any major impact event like the one that created Chicxulub is accompanied by one or more coeval impacts that leave smaller craters such as the Boltysh structure [13]. For example, the impact geometries of five craters with late Triassic ages - including the 100 km Manicouagan crater - suggest a multiple impact event was associated with the mass extinction at the end of the Triassic [14]. While subduction and sedimentation undoubtedly obscure the marine record of impact cratering, it is likely that data for some of the major marine impacts are captured by smaller, coeval terrestrial impacts. Therefore, we conclude that many of the major impacts have been included in our data set by our inclusion of smaller, well-dated craters. While the age data for major impacts are probably far from all-inclusive, the data set nonetheless probably represents a substantial fraction of the total number of the largest impact events, and certainly more than 2.5%.

In addition, it seems indisputable that the Earth and Moon have similar impact records given their close proximity, and Glikson himself documents similarities between their recognized impact records [7]. The age uncertainties for lunar spherules are large, and although we ignored age dates for lunar spherules with uncertainties >150 Myr and degraded the terrestrial record so that all data had errors of at least 45 Myr for the purposes of comparison, we look forward to the time when a more rigorous test of this model can be achieved using better-defined lunar spherule ages.

If there is any correlation between impacts and mantle plume volcanism, it is logical to infer that the largest impacts should have produced the clearest signal. However, statistical analysis of the data requires substantial smoothing because the ages of impact and mantle plume proxies are so poorly known. In particular, given the nature of the Precambrian record, and the limits on Precambrian geochronologies, it is unlikely that we will achieve a narrowing of the ages of any Precambrian events to the ±50000 year long period achieved for the Chicxulub impact event at any time in the near future.

We maintain that the age constraints currently available for events in these data sets require that some degree of smoothing should be done to obtain an appropriate statistical comparison. Because the data sets become more highly correlated as the smoothing increment increases [3], Glikson and others argue that the degree of correlation (e.g., 97%) is spurious. However, this could also indicate that our combined Earth/Moon data set, our smoothing technique, and our assumptions about lag times between impacts and associated plume activity are all valid. In our opinion, our approach provides yet another statistical test of the hypothesis that the impact of large extraterrestrial objects promotes or strengthens mantle plume volcanism [15 and 16]. The results indicate that the hypothesis is a reasonable one to pursue, as more qualitative assessments, including those of Glikson [17], previously have suggested. We eagerly await the improvements in mapping and geochronology that will permit more confident statistical correlations.[BOYLE]

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2. A.P. Van den Berg and D.A. Yuen, Delayed cooling of the Earth's mantle due to variable thermal conductivity and the formation of a low conductivity zone. Earth Planet. Sci. Lett. 199 (2002), pp. 403-413. SummaryPlus | Full Text + Links | PDF (608 K)

3. D.H. Abbott and A. Isley, Extraterrestrial influences on mantle plume activity. Earth Planet. Sci. Lett. 205 (2002), pp. 53-62. SummaryPlus | Full Text + Links | PDF (270 K)

4. P. Olson, G. Schubert and C. Anderson, Plume formation in the D' layer and the roughness of the core-mantle boundary. Nature 327 (1987), pp. 409-413. Abstract-GEOBASE | Abstract-INSPEC | Abstract-GEOBASE   | $Order Document | Full Text via CrossRef

5. T.B. Larson and D.A. Yuen, Fast plumeheads: Temperature-dependent versus non-Newtonian rheology. Geophys. Res. Lett. 24 (1997), pp. 1995-1998.

6. K.C. Condie, Mantle Plumes and Their Record in Earth History, Cambridge University Press, Cambridge, 2001, 306 pp.

7. A.Y. Glikson, Discussion of `Extraterrestrial influences on mantle plume activity' by D.H. Abbott and A.E. Isley, Earth Planet. Sci. Lett. 215 (2003) 10.1016/S0012-821X(03)00458-8, this issue.

8. T.S. Culler et al., Lunar impact history from 40Ar/39Ar dating of glass spherules. Science 287 (2000), pp. 1785-1788. Abstract-EMBASE | Abstract-INSPEC | Abstract-Elsevier BIOBASE | Abstract-GEOBASE   | $Order Document | Full Text via CrossRef

9. B. Chadwick, P. Claeys and B.M. Simonson, New evidence for a large Paleo-Proterozoic impact: spherules in a dolomite layer in the Ketilidian orogen, south Greenland. J. Geol. Soc. Lond. 158 (2001), pp. 331-340. Abstract-GEOBASE   | $Order Document

10. B.M. Simonson and P. Harnik, Have distal impact ejecta changed through time?. Geology 28 (2000), pp. 975-978. Abstract-GEOBASE   | $Order Document

11. A.Y. Glikson, Oceanic mega-impacts and crustal evolution. Geology (Boulder) 27 (1999), pp. 387-390. Abstract-GEOBASE   | $Order Document

12. E.M. Shoemaker, P.J. Hassig and D.J. Roddy, Numerical simulations of the Shoemaker-Levy 9 impact plumes and clouds. Geophys. Res. Lett. 22 (1995), pp. 1825-1828. Abstract-INSPEC   | $Order Document

13. S.P. Kelley and E. Gurov, Boltysh, an end-Cretaceous impact. Meteorit. Planet. Sci. 37 (2003), pp. 1031-1043.

14. J.G. Spray, S.P. Kelley and D.B. Rowley, Evidence for a Late Triassic multiple impact event on Earth; letter to the editor. Nature 392 (1998), pp. 171-173. Abstract-EMBASE | Abstract-INSPEC | Abstract-GEOBASE   | $Order Document | Full Text via CrossRef

15. M.R. Rampino and K. Caldeira, Major episodes of geologic change; correlations, time structure and possible causes. Earth Planet. Sci. Lett. 114 (1993), pp. 215-227. Abstract | Abstract + References | PDF (1059 K)

16. A.E. Isley and D.H. Abbott, Implications of the temporal distribution of high-Mg magmas for mantle plume volcanism through time. J. Geol. 110 (2002), pp. 141-158. Abstract-GEOBASE   | $Order Document | Full Text via CrossRef

17. A.Y. Glikson, Mega-impacts and mantle-melting episodes; tests of possible correlations, in: Y.A. Glikson, (Ed.), Thematic Issue; Australian Impact Structures, Australian Geological Survey Organisation, Canberra, ACT, 1996, pp. 587-607.

18. D.H. Abbott and A.E. Isley, The duration, magnitude, and intensity of mantle plume activity over the last 3.8 Ga. J. Geodyn. 34 (2002), pp. 265-307. SummaryPlus | Full Text + Links | PDF (329 K)
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