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CCNet DIGEST, 19 March 1999
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(1) MISSILE FEARS PUSH US TO UNVEIL SON OF STAR WARS
    THE TIMES, 19 March 1999

(2) THORIUM RESEARCH REVEALS PUNCTUATED LUNAR HISTORY
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(3) ORIGIN OF EARTH AND MOON: COLLIDING THEORIES
    Alex N. Halliday & Michael J. Drake, ETH Zentrum, Zurich

(4) ORIGIN OF EARTH AND MOON: A COUPLE OF UNCERTAIN AGE
    Frank A. Podosek, Washington University

(5) CHAOS IN THE OUTER SOLAR SYSTEM
    N. Murray & M. Holman, University of Toronto

(6) SEMIMAJOR AXIS MOBILITY OF ASTEROIDAL FRAGMENTS
    Paolo Farinella*) & David Vokrouhlický, Universitŕ di Trieste


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(1) MISSILE FEARS PUSH US TO UNVEIL SON OF STAR WARS

From THE TIMES, 19 March 1999
http://www.sunday-times.co.uk:80/news/pages/Times/frontpage.html?1617548

From Ian Brodie in Washington

RUSSIA and China yesterday attacked America's plans to revive its "Star
Wars" missile defence programme. A "Son of Star Wars" was passed
swiftly in the House of Representatives last night by 317 votes to 105
- a day after being overwhelmingly endorsed by the Senate. The two
Bills will now be combined and sent to President Clinton, who will sign
the legislation, having withdrawn his earlier veto threat.

The speed with which Mr Clinton and his fellow Democrats have reached
agreement with Republicans after years of partisan battling is a
reflection of growing worries over the development of missile 
programmes in North Korea, Iran, Iraq and possibly other rogue states.
The final blow came with revelations that China may have stolen US
nuclear missile know-how.

The Senate, by 97 to three, committed America to deploy a defence
against limited missile attacks "as soon as technologically possible".
The Bill did not specify a time frame or costs, but the Pentagon
envisages having radars to track incoming missiles, and land-based
interceptor missiles to shoot them down, by 2005.

The defences would be a scaled-back version of the anti-missile
umbrella based in space proposed 16 years ago by Ronald Reagan. His
dream proved technically impossible and lost its purpose with the Cold
War's end. The new proposal has revived Russian objections to Star Wars
- that it would breach the 1972 Anti-Ballistic Missile Treaty agreed by
Nixon and Brezhnev.

Both gambled that, if neither side had the means to defend its cities,
neither would be the first to attack. In time, trust and confidence
engendered by the ABM treaty led to the Start 1 and 2 agreements to
reduce nuclear arsenals. The Russian Foreign Ministry said that the
Senate Bill would undermine arms control agreements and posed a serious
threat to strategic stability. Russia has been resisting US proposals
to amend the ABM treaty to allow limited missile defences.

To underline the point, the State Duma this week introduced a Bill
making its ratification of Start 2 conditional on US adherence to the
treaty. To placate Moscow, Democrats persuaded Republicans to add
opaque language to the Senate Bill saying that America still supports
arms control and that Son of Star Wars must be consistent with policies
to cut Russia's nuclear stockpile.

China's misgivings are rooted in fears that similar technology will be
used to protect Taiwan. Blunt opposition was expressed by Zhu Rongji,
the Prime Minister.

Copyright 1999, The Times Newspapers Ltd.

=====================
(2) THORIUM RESEARCH REVEALS PUNCTUATED LUNAR HISTORY

From Andrew Yee <ayee@nova.astro.utoronto.ca>

Public Affairs Office (PAO)
Los Alamos National Laboratory

CONTACT: John Gustafson, 505-665-9197, pogo@lanl.gov

99-044

Thorium maps reveal complicated lunar history

LOS ALAMOS, N.M., Mar. 16, 1999 -- NASA's Lunar Prospector mission has
drawn great acclaim for its measurements of water ice at the moon's
poles, but equally important has been its steady effort mapping
geologic deposits around the surface of the cratered globe.

David Lawrence, a scientist at the Department of Energy's Los Alamos
National Laboratory, described some of the latest results in a
presentation today at the Lunar and Planetary Science Conference in
Houston. These new results include elemental distribution maps with
more than twice the resolution of previous Lunar Prospector results.

"These new data are quite spectacular," Lawrence said. "We're picking
out all the thorium hot spots and finding they are associated with
certain craters. We are also deriving the first estimates of absolute
thorium abundances, which represents the ground truth for modeling
lunar evolution."

Thorium is an important element for study because it is a constituent
of KREEP, the acronym for potassium (symbol "K"), rare Earth elements
and phosphorous. KREEP is the last material to solidify from a geologic
melt.

The moon once was hot and molten and as it cooled minerals crystallized
and sank to form the core, if they were heavy, or floated upward to
form the crust, if they were light. The elements in KREEP do not
readily incorporate into minerals and so the mixture remains molten the
longest. These elements, then, are signatures of the original material
under the moon's crust, and their presence on the surface indicates
some process -- volcanic events or impacts strong enough to punch
through the crust -- must have dredged them up from the interior.

Thorium emits gamma rays -- a high-energy form of light -- of a
distinct energy. A Los Alamos team built Lunar Prospector's gamma ray
spectrometer, which counts and measures gamma rays as Lunar Prospector
swings around the moon. Lawrence and his colleagues use this
information to create maps showing the abundance of thorium in
different locations.

"Because thorium is a tracer for KREEP-rich material, these data
provide fundamental information regarding the locations and importance
of geologic formations that are rich in KREEP-bearing materials,"
Lawrence said.

And they show that the moon's evolution was a complicated story.

Thorium emissions neatly trace out the outer rim of Mare Imbrium, one
of the distinctive features on the moon's Earthward-facing side.
Lawrence said this signal "provides a telltale sign of deposition by
ejecta. This indicates that around Mare Imbrium the dredge-up process,
at least in part, was related to an impact."

By contrast, the South-Pole Aitkin basin shows much less thorium-rich
material though it is the largest known impact crater in the solar
system. The impact presumably was large enough to poke through the
lunar crust to the moon's mantle material, but it did not encounter as
much thorium-rich material.

In addition to the gamma ray spectrometer, the Los Alamos team built
Lunar Prospector's neutron spectrometer and alpha particle
spectrometer. Data from the neutron spectrometer point to large
quantities of water ice at the moon's poles. The alpha particle data
could show signals of outgassing and hence geologic activity, but
analysis has not yet yielded definitive evidence of such events.

Alan Binder of the Lunar Research Institute in Gilroy, Calif., proposed
and leads the Lunar Prospector mission. NASA's Ames Research Center in
Moffett Field, Calif., controls mission operations.

Los Alamos National Laboratory is operated by the University of
California for the U.S. Department of Energy.

NOTE TO REPORTERS: Dr. Lawrence can receive messages during the Lunar
and Planetary Science Conference at (281) 488-0220 or by e-mail at
djlawrence@lanl.gov .

=======================
(3) ORIGIN OF EARTH AND MOON: COLLIDING THEORIES

Alex N. Halliday*) and Michael J. Drake: Colliding Theories. SCIENCE,
Volume 283, Number 5409 Issue of 19 Mar 1999, pp. 1861 - 1863

*) Department of Earth Sciences, ETH Zentrum, CH-8092, Zurich,
   Switzerland

When researchers try to find out how the Earth and the moon formed,
they quickly come up against the problem that direct evidence is
impossible to come by. Halliday and Drake discuss recent progress
towards understanding Earth and moon formation using simulations, high
pressure experiments and isotope geochemistry. The most widely accepted
theory assumes a "Giant Impact" scenario, in which two proto-planets
collide and the moon forms out of the debris created by this collision.
Many uncertainties remain, such as how large the two bodies were at the
time of impact, when the impact occurred, and whether it was
accompanied by the formation of deep magma oceans on Earth. © 1999 by
The American Association for the Advancement of Science.

======================
(4) ORIGIN OF EARTH AND MOON: A COUPLE OF UNCERTAIN AGE

Frank A. Podosek: Origin of Earth and Moon: A couple of uncertain age.
SCIENCE, Volume 283, Number 5409 Issue of 19 Mar 1999, pp. 1863 - 1864

*) Department of Earth and Planetary Sciences, Washington University,
St. Louis, MO 63130, USA

The earth and moon formed not long after our solar system formed 4.57
billion years ago, but the exact timing remains a subject of debate.
Attempts to date our planet and its companion are based largely on
isotopic measurements of lunar and terrestrial samples. Ratios of
certain isotopes can provide information on when the material formed,
but only if the physical and chemical changes that the material has
gone through are known. Podosek concludes that to improve the dating,
we need a better understanding of the physical and chemical processes
that affect planetary isotope compositions. © 1999 by The American
Association for the Advancement of Science.

====================
(5) CHAOS IN THE OUTER SOLAR SYSTEM

N. Murray *) & M. Holman: The Origin of Chaos in the Outer Solar System
SCIENCE, Volume 283, Number 5409 Issue of 19 Mar 1999, pp. 1877 - 1881

*) Canadian Institute for Theoretical Astrophysics, University of
Toronto, 60 St. George Street, Toronto, Ontario M5S 3H8, Canada.

Classical analytic theories of the solar system indicate that it is
stable, but numerical integrations suggest that it is chaotic. This
disagreement is resolved by a new analytic theory. The theory shows
that the chaos among the jovian planets results from the overlap of the
components of a mean motion resonance among Jupiter, Saturn, and 
Uranus, and provides rough estimates of the Lyapunov time (10^17 years)
and the dynamical lifetime of Uranus (10^18 years). The jovian planets
must have entered the resonance after all the gas and most of the
planetesimals in the protoplanetary disk were removed. ©1999 by The
American Association for the Advancement of Science.

====================
(6) SEMIMAJOR AXIS MOBILITY OF ASTEROIDAL FRAGMENTS

Paolo Farinella*) & David Vokrouhlický: Semimajor Axis Mobility of
Asteroidal Fragments. SCIENCE, Volume 283, Number 5407 Issue of 5 Mar
1999, pp. 1507 - 1510

*) Dipartimento di Astronomia, Universitŕ di Trieste, Via Tiepolo 11,
   I-34131 Trieste, Italy.

The semimajor axes of asteroids up to about 20 kilometers in diameter
drift as a result of the Yarkovsky effect, a subtle nongravitational
mechanism related to radiation pressure recoil on spinning objects that
orbit the sun. Over the collisional lifetimes of these objects
(typically, 10 to 1000 million years), orbital semimajor axes can be
moved by a few hundredths of an astronomical unit for bodies between 1
and 10 kilometers in mean radius. This has implications for the
delivery of multikilometer near-Earth asteroids, because the Yarkovsky
drift drives many small main-belt asteroids into the resonances that
transport them to the Mars-crossing state and eventually to near-Earth
space. Recent work has shown that, without such a drift, the
Mars-crossing population would be depleted over about 100 million
years, a time scale much smaller than the age of the solar system.
Moreover, the Yarkovsky semimajor axis mobility may spread in an
observable way the tight semimajor axis clustering of small asteroids
produced as a consequence of disruptive collisions. © 1999 by The
American Association for the Advancement of Science.

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