CCNet 27/2002 - 21 February 2002

"Mineral findings in two meteorites studied by University of Hawaii
scientists and mainland colleagues may change thinking about the
solar system's age. If their analysis of two major components is
correct, "the whole idea about the chronology of the solar nebula can be
wrong," said Alexander Krot, associate researcher at the Hawaii Institute of
Geophysics and Planetology."
--Helen Altonn, Honolulu Star-Bulletin, 19 February 2002

"Not only lava, but water has recently flooded from fissures near
Mars' equator, University of Arizona scientists have discovered....
The images showed geologic evidence for catastrophic floods similar
to catastrophic flood landforms on Earth."
--Lori Stiles, University of Arizona

"Nuclear propulsion and nuclear power in space are technologies
long-overdue for investment and development. They mean traveling quicker
as well as doing more once you have arrived at your destination - but one
must keep perspective: they are also not a panacea to all of our
current space transportation limitations."
--Ralph McNutt, Johns Hopkins University, 20 February 2002


    Honolulu Star-Bulletin, 19 February 2002

    Ron Baalke <>

    Joel Parker <>

    Space Daily, 20 February 2002

    Andrew Yee <>

    inScight, 20 February 2002

    Dave Wright <>

    Jonathan Shanklin <>

    Jonathan Shanklin <>

     Christian Glowinski <>

(11) ... AND AN ANSWER
     Duncan Steel <>

     Nathalie Bugeaud <>


>From, 19 February 2002

By Joe Rao

A newly discovered comet, now approaching the Sun and Earth, could develop
into a relatively bright naked-eye object in coming weeks, researchers say.
The best views of the comet may be reserved for those under dark skies far
from bright lights, but even city dwellers should be able to spot it.

Kaoru Ikeya of Japan and Daqing Zhang from China first sighted the comet in
the constellation Cetus, the Whale, on Feb. 1. Both described it as a weak,
condensed glow in their telescopes with no mention of a tail.

The comet is called Ikeya-Zhang. The latest orbit calculation indicates it
will pass closest to the Sun, a point called perihelion, on March 18 at a
distance of 47.1 million miles (75.8 million km). After rounding the Sun,
the comet will continue moving toward Earth, making its closest approach to
our planet, called perigee, on April 28, when it will be 37.6 million miles
(60.5 million km) away.

Ikeya-Zhang's expected path across the sky in the coming weeks will greatly
favor Northern Hemisphere observers. During most of March on into early
April, the comet will be visible near to the north-northwest horizon about
an hour after sundown. Bright moonlight may hinder observations during the
last week of March.

After the first week of April, with the Moon no longer a factor, the comet
will also be visible in the morning sky, rising earlier and getting
progressively higher above the northeast horizon each night.

Seen before?

Initially, it appeared that this comet would not get brighter than fourth
magnitude, which is similar to the brightness of a relatively dim star.
Magnitude is a measure of a celestial object's apparent brightness.

But John Bortle, a longtime comet consultant for Sky & Telescope magazine,
said it could get brighter.

Soon after Ikeya-Zhang's orbit was calculated, some orbital specialists
noticed a similarity to a pair of much earlier comets that appeared in 1532
and 1661, Bortle explained in an e-mail interview last week. The 1532 comet,
in particular, was apparently a bright comet according to Oriental records.

Brian Marsden of the Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, an orbital specialist, said last Thursday that "a revolution
period of 400-500 years (for Ikeya-Zhang) is likely," keeping alive
speculations that this may be a return of the 1532 comet.

The key to figuring out if the comets are the same may lie in Ikeya-Zhang's
orbital period -- how long it takes to go around the Sun.

"In recent days, several observers have made their own independent
calculations suggesting that Ikeya-Zhang might have an orbital period of
roughly 500 years, making for a strong argument that there may indeed be a
direct connection with the comet of 1532," Bortle said.

What to expect

How comet Ikeya-Zhang ultimately performs is anyone's guess. So far it is
brightening more rapidly than originally expected. As of late last week, it
had nearly doubled in brightness in just one week and was at magnitude 6.8
as of Feb. 15.

But Terry Lovejoy, an assiduous comet watcher from Australia, says it's a
bit early to get excited.

"We've seen this situation before," Lovejoy cautions. "At first a new comet
appears to brighten at a much faster than normal rate, but then as it gets
closer to the Sun it seems to run out of puff. My best guess is that this
comet will be no different and will peak somewhere at around magnitude 3.5."

Such a brightness is just slightly fainter than Megrez, the star in the Big
Dipper that joins the handle with the bowl.

"A peak of magnitude 3.0 would not be at all surprising to me," says Bortle,
adding that he expects Ikeya-Zhang to unfurl an impressive tail perhaps up
to 15 degrees in length as it sweeps by the Earth. For comparison, your fist
held at arm's length measures roughly 10 degrees. However, because this tail
is likely to be chiefly composed of gas and not dust, it will appear faint
and bluish and likely only be visible to those with access to dark skies
free of light pollution.

So how might Ikeya-Zhang stack up against other popular comets?

The 1986 appearance of Halley's comet, considered disappointing by many,
also peaked at around magnitude 3.0. In contrast, comet Hale-Bopp, which put
on a memorable show in April 1997, attained a brightness close to magnitude
-1, or about 60 times brighter than Halley.

Binoculars or a small telescope should allow most skywatchers a view of
Ikeya-Zhang's fuzzy head, called a coma, and of the tail.

Editor's Note: Viewing tips and more information about comet Ikeya-Zhang
will be provided in our Spacewatch section in March.

Copyright 2002,


>From Honolulu Star-Bulletin, 19 February 2002

UH scientists report that planets may have formed very quickly

By Helen Altonn

Mineral findings in two meteorites studied by University of Hawaii
scientists and mainland colleagues may change thinking about the solar
system's age.

If their analysis of two major components is correct, "the whole idea about
the chronology of the solar nebula can be wrong," said Alexander Krot,
associate researcher at the Hawaii Institute of Geophysics and Planetology.

The researchers have dated one component at 4.568 billion years, plus or
minus 1 million or 2 million years, and they will try next to define the
absolute age of the second major component.

"If we find they're the same," Krot said, "basically it will tell us
probably the disk around the sun existed mostly only 1 million years, and
planets formed very quickly."

Krot and HIG planetary scientist Edward Scott collaborated with Kevin
McKeegan of the University of California-Los Angeles, Laurie Leshin of
Arizona State University and Glenn MacPherson of the U.S. National Museum of
Natural History.

They analyzed particles from meteorites Efremovka, landing in Russia in
1962, and Vigarano, which landed in Italy in 1910. They are fresher than
other meteorites, the scientists said, because they were in part of an
asteroid that was not so weathered.

A paper describing their findings appears in the Feb. 8 issue of the journal

Scott said the primitive meteorites (chondrites) contain little particles
the researchers think were formed in the dust and gas disk (the solar
nebula) that formed at the same time as the sun, and from which all planets
were formed.

Two of the major components are calcium-aluminum-rich inclusions (CAIs) and
chondrules. CAIs contain abundant calcium and aluminum oxides, while
chondrules are richer in iron, magnesium and silicon oxides.

If they can date the origin of the CAIs and chondrules, Krot said, "we can
say when they formed and what is the age of our solar system."

Originally, it was thought the disk lasted 50 million years around the sun
before planets formed, he said. That shrank to 10 million years, and now
people are talking about the solar nebula lasting 1 million to 5 million
years, he said.

According to their analysis, the two major components formed in different
parts of the solar nebula and have very different gas composition.

Krot said they found differences in isotopes (oxygen atoms) in regions where
the components formed. People generally have associated those differences
with age differences, saying CAIs formed first and chondrules later, he

But their findings potentially show the isotopic differences have nothing to
do with age, he said.

"It could just be spatial differences, so regions where the two components
formed existed at the same time, but isotopic signatures of the two regions
were different."

Scott said if you pick up meteorite rocks from Mars or the asteroid belt,
the three oxygen isotopes are proportionately different.

Techniques in their field allow them to define age within 1 million years,
Krot said, explaining the next step is to define the absolute age of

The fact that the components have isotopic differences does not mean they
formed at different times, he said. One explanation may be that CAIs formed
close the sun and chondrules formed further away, he added.

Many people have been studying meteorites 30 to 40 years trying to
understand how the major components formed, Scott said.

"It has been a tough struggle, particularly because we have to imagine
what's happening.

"Now, we're getting a lot more information from astronomers who can see more
how stars are forming. That's where we hope the breakthrough is coming, so
we can relate in more detail what we're seeing to what astronomers are
telling us about stars."

© 2002 Honolulu Star-Bulletin


>From Ron Baalke <>

>From Lori Stiles, UA News Services, 520-621-1877
February 20, 2002

The drilling crew on the Chicxulub Scientific Drilling Project near Merida,
Yucatan, Mexico, has been doing "a fantastic job," last week recovering
between 35 and 40 meters of exceptional core samples each day, according to
a University of Arizona scientist and co-investigator on the project.

The Chicxulub Scientific Drilling Project (CSDP) is an international project
to core 1.8-kilometers into an immense crater created by the impact of an
asteroid or comet 65 million years ago. The Cretaceous-Tertiary (K/T) impact
is thought to have led to one of the greatest mass extinctions in Earth
history, including dinosaur extinction.

Universidad Nacional Autonoma de Mexico (UNAM) is the lead institution on
the $1.5 million, approximately 2-month project. The goal is to discover
what the impactor was and the details of the catastrophic impact that wiped
out more than 75 percent of all plant and animal species on Earth.

"The crew is drilling 24 hours a day, 7 days a week, at a far faster pace
that we ever thought possible," said UA planetary scientist David A. Kring.
"We had hoped to recover as much as 25 meters of core samples each day, but
at the rate they are drilling, we will probably reach depths of 1.5
kilometers by the end of the project, despite the loss of a diamond drill
head earlier in this effort."

The CSDP drilling team members are from DOSECC (Drilling, Observation, and
Sampling of the Earth's Continental Crust, Inc.), and Pitsa, a drilling
contractor in Mexico.

"We are getting a 100 percent core-recovery rate," Kring added. Scientists
by such drilling operations often recover only between 50 percent or 60
percent, and sometimes as little as 20 percent, of intact core samples, he

The drilling crew hands each core barrel pulled from the crater to onsite
geologists who then remove and process the core samples.

Kring and UA undergraduate student Jake Bailey last week helped relieve
their tired Mexican colleagues in onsite geology duties, working 12-hour
shifts. Kring worked a 28-hour stretch as well.

When Kring left Chicxulub last Saturday night, the team had drilled to more
than 1.2 kilometers (4,200 feet).

Kring, director of the NASA/UA Space Imagery Center, has posted photographs
and more details on recent operations on the Space Imagery Center website at

For more about the Chicxulub Scientific Drilling Project, point your web
browser to:

Contact Information
David A. Kring


>From Joel Parker <>

The New Horizons Pluto-Kuiper Belt project will hold a 2-day workshop in
Boulder, Colorado on May 20 and 21, in support of mission science and broad
mission participation by community members.  The New Horizons project is
organizing this workshop in order to better inform the community of mission
plans and participation opportunities, and to solicit community input on
scientific topics relating to mission planning at Pluto-Charon.  The
specific themes of this workshop are: predictions for the time of the
encounter, and groundbased and spacebased observations through 2015 in
support of encounter planning.

for workshop details.


>From Space Daily, 20 February 2002

In the decades ahead nuclear propulsion systems will underpin an expanded
outerplanets exploration program. In the meantime, one final chemical
propulsion mission to the last unvisited planet remains an urgent priority
before pluto's atmosphere collapses

by Ralph L. McNutt, Jr.
Washington - Feb 20, 2002

In the proposed budget for Fiscal Year 2003 NASA has announced a major new
technology development initiative in nuclear power and nuclear propulsion. A
renewed commitment by NASA to develop nuclear propulsion for deep-space
travel can only be applauded. But there are many popular misconceptions
about nuclear propulsion, and with a time-critical mission to the planet
Pluto in the balance, it is timely to discuss what in-space nuclear
propulsion is - and what it is not.

The Nuclear Knot for Pluto

It is a truism that nuclear propulsion is not yet developed, but it is
important to understand the full import of that fact.

Even optimists doubt that a first nuclear test flight could take place in
less than six to eight years, and, as with DS-1 for solar electric
propulsion, a nuclear test flight will be required to validate the new
technology. Given the difficult launch approval process such a propulsion
stage will no doubt require, it could well be longer.

There is no guarantee that such a multi-year development will eventually
lead to a flight program, and previous U.S. efforts in developing nuclear
technology for spacecraft give no cause for optimism.

>From the nuclear thermal NERVA program (1960s) through the nuclear electric
SP-100 (1980s) program, nuclear propulsion has always not quite "gotten off
the ground." None of this past track record means it is a bad idea, but it
does mean that it is technically, and politically, difficult.

Even given a working nuclear propulsion stage, if you want to go somewhere
fast, then you must also slow down near the destination in order to obtain
sufficient time to make observations.

This is a new problem for mission planners who heretofore only needed to
worry about slowing a spacecraft, and typically by far less speed, to go
into orbit. This problem is exacerbated in the outer solar system, where
illumination levels are relatively low. At Pluto, light levels are 1000
times lower than in the sun-drenched regions near Earth.

Nuclear propulsion does not guarantee unlimited peak speeds either.

A recent study by the Johns Hopkins University Applied Physics Laboratory
and Glenn Research Center examined optimistic spacecraft architectures
(meaning no one really knows how to build them yet) and found that a nuclear
electric system could only cut about 2 years off the the 9.5 year flyout
planned for the current PKB mission-New Horizons.

This flight time does not include slowing down to increase the period of the
main flyby time and collection of observational data which will make the
nuclear option take even longer than found in the study.

The net comparison means that a nuclear option for Pluto will arrive years
later (given the development time needed for nuclear propulsion), at
significantly more expense (nuclear propulsion is not going to be free), and
with greater technical risk than what is on the table now (the New Horizons
development effort).

A change to nuclear-based propulsion will lead to a better program of
exploration; we must just be careful not to hamstring current efforts during
that transition.

The Nuclear Advantage

Nuclear propulsion, once developed and certified for use, holds much promise
for many future applications in planetary science. Indeed, there are whole
classes of mission that nuclear propulsion will enable once it is developed.

A good analogy can be drawn with solar electric propulsion (SEP) and the
recently selected Dawn mission in NASA's competitive Discovery program.
Prior to the validation of SEP as a primary deep-space propulsion system
with DS-1, NASA was unwilling to select missions like Dawn due to perceived
risk of failure.

A DS-1 flight plan could have been flown with a chemical propulsion system,
but a mission to orbit the mainbelt asteroids, Dawn's mission, clearly could
not. In this case, SEP is an enabling technology because the mission simply
cannot be done with existing launch vehicles, spacecraft we can actually
build, and ANY form of chemical propulsion. Where the true promise of
nuclear electric propulsion (NEP) lies is in similarly otherwise undoable
missions in the outer solar system.

Maximizing the scientific return from a wider set of enabled possibilities
is what turning the science community loose in a competitive environment is
good for. The competitive "New Frontiers" program, coupled with nuclear
propulsion promises the same high value return that NASA is beginning to
reap with solar electric propulsion and the Discovery program closer to the

The Power Connection

In-space nuclear power is intimately connected to in-space nuclear

In high priority Mars surface missions using rovers, as well as in the outer
solar system, light levels are simply too low to provide enough electrical
power to do all that the science requires.

Better solar cells will not fix the problem, as the technology is pushing
close to the power-generation limits imposed by physics, and nuclear power
sources are required for long range rovers on Mars and most missions beyond
the main asteroid belt, where radioisotope thermoelectric generators have
been the workhorse of all outer planet missions for decades.

One area that needs development is more efficient power converters for
radioisotope power supplies, and one solution could be mechanical Stirling
converters that show promise for better conversion efficiency.

Coupled with continued NASA investments in lighter and more power-efficient
spacecraft subsystems new radioisotope power units married to ion engines
can enable the first generation of nuclear propulsion exploration to be

With time and money, it should be possible to make the same amount of
electricity with less plutonium, another win-win situation. In some sense,
such systems are a stopgap for the application of small fission reactors
that can provide far more power. The fission systems have further to go in
development, but nuclear space propulsion need not wait as radioisotope
electric propulsion will get us started.

The Bottom Line

Nuclear propulsion and nuclear power in space are technologies long-overdue
for investment and development. They mean traveling quicker as well as doing
more once you have arrived at your destination - but one must keep
perspective: they are also not a panacea to all of our current space
transportation limitations.

The development of these new resources is also not without risk, technically
or politically; and while risk does not mean one should not implement new
research programs, the presence of risk does mean that one should not overly
count on positive results in a time-critical endeavor. And the exploration
of Pluto is such an endeavor.

Advantages must be seized wherever and whenever possible; they are all too
few in the space exploration business.

The last real chance to get to Pluto with current technology requires a
launch in January 2006 (the curent New Horizons mission plan). Given where
we are with NEP, that technology would surely take longer to implement, cost
more money, and delay the encounter past that achievable with New Horizons.

With a hammer that promises far larger payloads and missions, such as
extensive orbital tours that are not feasible today, nuclear propulsion
deserves developing. We need nuclear propulsion and the time and money to
get it right. While we are not there yet, NASA has taken a major step in the
right direction.

Dr. Ralph McNutt is the Chief Scientist of the Space Department at the Johns
Hopkins University Applied Physics Laboratory. He is also the Project
Scientist for the MESSENGER Discovery mission to Mercury and a Co-I on the
New Horizons concept under study for a Pluto-Kuiper Belt mission. All of the
opinions expressed are his own and should not be construed as reflecting the
position of the Applied Physics Laboratory or the Johns Hopkins University."

Copyright 2002, Space Daily


>From Andrew Yee <>

News Services
University of Arizona
Tucson, Arizona

Contact Information:
Devon Burr, 520-621-4824,
Alfred McEwen, 520-621-4573,

Feb 19, 2002

Floods at Mars' Equator Are Recent, UA Scientists Say
By Lori Stiles

Not only lava, but water has recently flooded from fissures near Mars'
equator, University of Arizona scientists have discovered.

And they're not talking about a trickle. They're talking possibly 600 cubic
kilometers of water. That's one and a quarter times as much water as in Lake
Erie, four times as much water as in Lake Tahoe, and 65 times as much water
as in California's Salton Sea.

"This is a completely different water release mechanism than previously
studied on Mars," said Devon Burr, a UA doctoral candidate in geosciences.

She and UA planetary scientist Alfred S. McEwen analyzed new Mars Orbital
Camera (MOC) images near a series of fissures that stretch more than a
thousand kilometers (600 miles) across the lava-covered Cerberus Plains just
north of the martian equator. The images showed geologic evidence for
catastrophic floods similar to catastrophic flood landforms on Earth. They
and Susan Sakimoto of the NASA Goddard Space Flight Center have reported the
research in Geophysical Research Letters.

UA Regents' Professor Victor Baker and others concluded from Viking
spacecraft images more than 20 years ago that great water floods must have
carved huge channels draining into another region of the planet, Chryse
Planitia. But photographic evidence consistently confirms that happened more
than 2 billion years ago.

Burr and McEwen analyzed the Athabasca Valles channel system that branches
south and southwest from the Cerberus Fossae.

"Athabasca Valles is an almost new component in the martian hydrological
cycle," Burr said.

"What's different here is that this is very recent, and the water source is
nothing like we have on Earth," she said. "The water here gushed from
volcano-tectonic fissures. While the fissures themselves may be older, the
latest eruption of water was probably only about 10 million years ago."

"That's young," McEwen said. "If there is anyplace on Mars where there are
current geothermal anomalies, I myself would look in the Cerberus Fossae

Geothermal sites on Mars would be a striking discovery, for they would
provide both heat and water on the cold, dry planet.

"Flood volcanism on Earth occurs about every tens of millions of years,"
McEwen said. "The last such event was 10 million years ago. But that doesn't
mean it's over. It will happen again. The  same is probably true on Mars --
geologically speaking, it's still active."

Tectonic forces, or a combination of tectonic and magmatic forces, likely
created the fossae, or fissures, from which lava extruded over the Cerberus
Plains, McEwen said.

New MOC images show the fossae to be the source of recent, at least small
lava flows. And new Mars Orbiter Laser Altimeter (MOLA) data reveals they
are the source for much larger flows as well, he added.

Researchers know of one other possible such volcanic/hydrologic channel
system on Mars, Mangala Valles, also near the equator. But it, too, is older
than Athabasca Valles.

The most distinctive evidence for aqueous flooding are steamlined,
flat-topped mesas in the middle of channels. These tear-drop shaped features
are similar to structures in the Channeled Scabland in the northwestern
United States, which Baker in 1982 reported were features created by
catastrophic outflow of glacial meltwater.

The Athabasca Valles streamlined mesas on Mars rise 100 meters (330 feet)
above the channel floors at their upslope ends and range from a few hundred
to a few thousand meters long. Their flat upper surfaces "support an aqueous
origin rather than a glacial one," the scientists conclude in their paper.

The mesas are composed of fine, horizontal layers behind impact craters,
adding to evidence that were formed by deposition during flow in the lee of
an object. Other streamlined forms, also layered but not flat-topped like
the streamlined mesas, more likely were formed by erosion during floods over
pre-existing layered terrain, Burr said.

The new images also detail that the broad channel floor is often lined with
grooves and ridges running parallel to the streamlined mesas or to the
channel walls. The grooves, about 100 meters wide (330 feet) and 10 meters
deep (33 feet) and similar to Channeled Scabland grooving, cover as much as
100 square kilometers (more than 38 square miles) in a single image.

All fluvial features were seen down slope, or southward, of the Cerberus
Fossae. The fissures have such sharp edges and such steep slopes -- more
than 80 degrees -- and cut through such young, lightly cratered lava plains
that they must have been active recently, the researchers said.

UA planetary sciences graduate student Peter Lanagan, McEwen and colleagues
previously reported on "rootless cones" at the downstream ends of the
channel. The martian cones are similar both in morphology and size to
rootless cones in Iceland, features which form when surface lava interacts
explosively with near-surface groundwater. The most plausible source of
water that produced rootless cones on Mars is a catastrophic flood, they

Because the flood water was debouched over permeable lava, much of it may
have been absorbed by the lava and still persist in the Cerberus Plains as
shallow ground ice, Burr, McEwen and Sakimoto conclude.

The shallow ground ice and the record of recent geothermal activity are
likely present in the Cerberus Plains, making it an important target for
future Mars exploration, the UA scientists note. As leading astrobiologists
posit, "Both shallow ground ice and geothermal deposits are important
targets in the search for a record of Martian life."

PHOTO/CAPTIONS: Mars Orbiter Camera and Mars Orbiter Laser Altimeter images
of Cerberus Fossae and associated channels analyzed in the Burr, McEwen and
Sakimoto paper are available via Internet at


>From inScight, 20 February 2002

The worst day in the past half-billion years was likely that one 65 million
years ago, when a mountain-size asteroid or comet slammed into the Yucatán
Peninsula. Life on Earth changed forever: The dinosaurs disappeared, and
mammals seized the day. The immediate cause of the dinosaurs' extinction has
long been listed as starvation after an enormous pall of dust blocked the
sun and killed off the plants. But now a geologist says the ancient impact
didn't kick up that much dust after all.

To cut off photosynthesis and starve the dinosaurs, huge amounts of tiny
particles--smaller than 1 micrometer in diameter--would have to have floated
in the atmosphere for months. By now this fine dust would have weathered
away to clay. So geologist Kevin Pope of Geo Eco Arc Research in Aquasco,
Maryland, scoured the literature for reports of the size and abundance of
larger, more rugged particles in the 3-millimeter-thick, global layer of
impact debris. From these measurements, Pope tried to understand the
dispersal of the entire dust cloud.

In the February issue of Geology, Pope reports that the size of the larger
debris dropped off sharply away from the impact, suggesting it had fallen
from wind-blown debris clouds rather than being blasted around the globe by
the impact. Indeed, when Pope modeled debris dispersal by winds alone, the
distribution of debris grains resembled that seen in the global debris
layer--but only if the impact produced a relatively small amount of debris.
In addition, assuming that the impact debris had a distribution of particle
sizes similar to that of volcanic ash, Pope concludes that less than 1% of
the debris consisted of submicrometer particles. Therefore, the dust in the
global layer is two to three orders of magnitude less than that needed to
shut down photosynthesis, he writes.

Planetary physicist Kevin Zahnle of NASA's Ames Research Center in Mountain
View, California, tends to agree that dust was not the likely killer. Zahnle
thinks the most likely alternative is the sun-blocking smoke caused by a
global fire. If dust really wasn't to blame, then the environmental damage
from future impacts might be less disastrous than researchers have generally
assumed. But, as Zahnle cautions, because the only data come from a single
huge example, taking a lesson from the death of the dinosaurs is fraught
with difficulty.


© 2001 The American Association for the Advancement of Science

MODERATOR'S NOTE: For more responses to Pope's paper see:


>From Dave Wright <>

Sponsored by British National Space Centre, ASTRIUM and BIS

Annual Conference at CHARTERHOUSE SCHOOL
Nr Godalming Surrey
2nd, 3rd and 4th of April 2002

UK Space History, Policy and Education
With 30 speakers Topics will include:
Beagle 2, Spacetug, Thor, Blue Streak, Hydrogen Work in the UK, Space
Tourism, Hypersonic Flight, German Aeronautical data collected in 1945, The
Cold War, Chevaline, Polaris, Satellite propulsion systems, Running a Trials
team, Managing Aerospace Projects 50s-70s, Model Rockets, The Rocket Post
and much more.  

For more details e-mail, visit the conference web page at
or write 17, Elsmere Avenue, Aigburth, Liverpool, L 17 4LB

Supported by ASTRA, Royal Aeronautical Society,
Space Education Council, and UKSEDS
Limited number of student bursaries available thanks to BNSC



>From Jonathan Shanklin <>

The latest orbit for this comet actually has perihelion on March 18.9, and
suggests that it may be a return of a comet seen in 1532 (C/1532 R1). My
analysis of the observations shows that it is brightening as 15 log r and
could therefore reach 2nd magnitude in the second half of March.  It remains
relatively low in the evening sky until towards the end of March (moonlight
also interferes), but is well placed in the moonless period of the first
half of April.

Jonathan Shanklin
British Antarctic Survey, Cambridge, England

British Astronomical Association, Comet Section


>From Jonathan Shanklin <>

Brian Marsden notes in IAUC 7832 that SOHO comets 1999 J6, 1999 U2, 2000 C3
and 2000 C4 form a group with q=0.049 and i=25. 

Members of this group can pass quite close to the Earth if they have
perihelion around May 11 - 12. If they survive perihelion, they then make a
close approach to the Earth around June 10 - 11 and would become visible
from the northern hemisphere. Otherwise members of this group are best seen
from the southern hemisphere.

Comet 1999 J6 fills this criterion and is a new addition to the list of
close earth approachers.  With T = 1999 May 11.59 the comet could have
reached 11th magnitude between 1999 June 9 and 11, when it was 0.03 AU from
the Earth. It would have been brighter than 20th mag until early July.
Unfortunately the LINEAR skyplot shows that the comet was outside their
observing region in June and probably too faint by July. 

Jonathan Shanklin
British Antarctic Survey, Cambridge, England

British Astronomical Association, Comet Section


>From Christian Glowinski <>


here's something concerning the "NEO flux" that I do not understand (yet).

Suppose the impact frequency of tunguska-sized (H= 23...25mag) objects is 1
per 300 years.

The earth's radius is about 1/60 of the moon's distance, so the target area
of a "moon crosser" would be 3600 times larger than that of an impactor, and
now divide 300 years by 3600 - looks like there should be 1 of these objects
passing by the earth at a distance closer than the moon each *month*. While
tunguska-sized objects are found quite frequently by the NEO surveys,
none has ever been been recorded closer than the moon (0.00256 au, see , the biggest "moon
crossing" object listed there is  2001 BA16, H= 25.8)

So what's wrong with these statistics?


Christian Glowinski
Bremen, Germany

(11) ... AND AN ANSWER

>From Duncan Steel <>

Dear Benny,

With regard to the question from Christian Glowinski:

(a) Nothing is wrong with the statistics (except that I believe the
  "Tunguska rate" is likely closer to once per century rather than
  once per 300 years - but that is a triviality).

(b) Another triviality that upsets the sums very slightly is the fact
  that objects striking the Earth have been subject to gravitational
  focussing. This has the effect of producing a collision cross-section
  that is larger than the Earth's geometrical cross-section. The
  enhancement factor is speed-dependent, but it is typically around
  two or less (it is only much greater for very low-speed arrivals). So
  again it's a small factor.

(c) The real answer to the basis of Christian's question is that indeed
  there are many small (Tunguska-type) asteroids passing "close" by the
  Earth (that is, passing through cis-lunar space), but the majority of
  them are not detected.

This is not news: many of us in the game have pointed this out in books,
magazines, and radio and TV interviews over the past decade or more. For
example, in "Rogue Asteroids and Doomsday Comets" (Wiley, 1995), referring
to the few *detected* near-missers, I wrote that "These comprise only a
small fraction of the total that passes closer than the Moon, however, with
more than 99% undoubtedly escaping unseen."

Nor is this surprising. Even now the sky is being searched typically only
once per month (to various limiting magnitudes): perhaps several times for
parts of the northern sky, but the southern sky not at all. On the other
hand, it takes a typical asteroid that is passing through cis-lunar space
less than ten hours to do (i.e. transit time through the centre of a sphere
with radius 384,000 km), and that is when it would be brightest. It would
also be moving at its highest angular speed, making the probability of
detection lower than if the angular speed were moderate (i.e. during an
exposure its reflected light is "smeared out"). So what do you expect?

Bottom line: most small NEAs pass by the Earth unobserved.


Duncan Steel


>From Nathalie Bugeaud <>

Dear Benny,

Dr Landis said (AAAS press release, CCNet 18 Feb 2002): "After the long
voyage without any men present, they may discover that humanity doesn't
actually need men after all and they'll engineer a society without them. But
then, maybe that will be better anyway. It certainly might be worth a try".

My letter to the editor letter reads:

Dear Editor,

So Mr Mark Henderson and the American Association for the Advancement of
Science think that men will not be travelling to the stars because our
future female star travellors will save weight by taking a sperm bank.

Their knowledge and judgement has obviously been blinded them by their
hatred of men since they should realise that research is well advanced on
the harvest and storage of human eggs and the artificial womb should be
fully functional long before we head out to the stars.

Hopefully, humans will not export the rampant misandry which is currently
dominating the thoughts of some people in research and the media.

Nathalie Bugeaud

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