PLEASE NOTE:
*
Date sent: Wed, 10 Dec
1997 14:03:42 -0500 (EST)
From:
HUMDRICH <D.J.RICHARDSON@livjm.ac.uk
Subject: CC
DIGEST, 10/10/97
To:
cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRDIGE-CONFERENCE DIGEST, 10 December 1997
To be or not to be - that is the question when it comes to icy
mini-comets and life on Mars. Scientific minorities and
majorities
battle it out, yet again. Does anyone like to wager on the
outcome of
these two astrophysical races?
Benny J Peiser
-----------------------------------------------------------------
(1) NASA ATTEMPTS TO FIND SMALL COMETS
(2) WHAT'S IN AN IMAGE : INSTEAD OF COMETS, SCIENTISTS CAN
ONLY SEE
'NOISE'
(3) MARTIAN METEORITE CONTAINS NO BIOLOGICAL LIFE, RESEARCH TEAM SAYS
======================================================================
Bill
Steigerwald
Dec. 5,1997
William.A.Steigerwald.1 @gsfc.nasa.gov (Phone: 301-286-5017)
RELEASE NO: 97-173
(1) NASA COORDINATES EFFORT TO INDEPENDENTLY VERIFY SMALL COMETS
NASA is leading an interagency effort to search for the small,
water-bearing comets that have been reported by Dr. Louis Frank
and
Dr. John Sigwarth of the University of Iowa based on their
observations from the an instrument on NASA's Polar
spacecraft. The
search effort was launched in response to requests from the
scientific community for independent verification of the
existence of
the small comets.
NASA has assembled a steering group that is providing advice
on the
how to search for the small comets through new observations or
through archived observations made by other spacecraft. The
steering
group is headed by Dr. Robert Hoffman, an astrophysicist in the
Electrodynamics Branch of NASA's Goddard Space Flight Center
(Greenbelt, Md.) and the project scientist for Polar.
Hoffman will discuss "The Search for Small Comets"
during a
presentation scheduled for 3:45 p. m. PST on Tuesday, Dec. 9, in
room
134 of San Francisco's Moscone Center. The talk is part of
the
scientific session "Origins--Topics in Space Physics and
Planetology:
Planets and Comets" at the Fall Meeting of the American
Geophysical
Union.
To date, the steering group has promoted the exchange of data
and
information and has coordinated some search activities. The
searches
fall into three categories: evaluation of Polar data, new
searches
based on Polar optical data, and searches based on
interpretations of
the Polar data.
Researchers have conducted or are making plans to conduct
optical
telescope and radar searches for evidence of the small comets
before
and after their disruption. Indirect searches will include
studies of
the coma of the Moon and of the deposition of water vapor in
Earth's
atmosphere.
Researchers have investigated the possibility that the source
of the
comet observations is ice from the spacecraft itself.
Initial
results do not support this theory.
The small comets steering group, chaired by Hoffman, includes
Dr.
Michael A'Hearn from the University of Maryland; Dr. Art Aikin
from
NASA Goddard; Dr. Richard Behnke, head of the Upper Atmospheric
Research Section of the National Science Foundation; Dr. Andrew
Christensen from The Aerospace Corp.; Dr. Robert Meier from the
Naval
Research Laboratory; Dr. Ching Meng from Johns Hopkins
University's
Applied Physics Laboratory; Richard Vondrak, chief of the
Laboratory
for Extraterrestrial Physics at NASA-Goddard, Major Martin Whelan
of
the U.S. Department of Defense; and Dr. George Withbroe, science
program director for Sun-Earth Connections in NASA's Office of
Space
Sciences.
========================================================
WHAT'S IN AN IMAGE: INSTEAD OF COMETS, SCIENTISTS CAN ONLY SEE
'NOISE'
Date: Mon, 08 Dec 1997 11:19:47 -0700
From: Lori Stiles <lstiles@U.Arizona.EDU
Subject: UA 'Small Comet' Skeptics
CONTACTS:
Alex Dessler, 520-621-4589, dessler @arizona.edu
Jennifer Grier, 520-621-1507, jgrier@lpl.arizona.edu
David Kring, 520-621-2024, kring@lpl.arizona.edu
Alfred McEwen, 520-621-4573, mcewen@pirl.lpl.arizona.edu
Bashar Rizk, 520-621-1160, bashar@lpl.arizona.edu
Timothy Swindle, currently collecting meteorites in Antarctica;
after January, 520-621-4128,
tswindle@lpl.arizona.edu)
Earth's sky would sparkle like a Christmas tree, its air would
hold
at least 30,000 times more inert gas and its moon would be pocked
with
millions more bright-spot craters than spacecraft see if a
prominently
publicized small-comet theory were correct, scientists from The
University of Arizona in Tucson report in the Dec. 15 issue
of
Geophysical Research Letters.
University of Iowa physicist Louis A. Frank and his former
graduate
student announced last May in a NASA news release and at an
American
Geophysical Union news briefing that images from their Visible
Imaging
System on the Polar spacecraft show Earth is showered by a steady
stream of water-packed objects, small comets that bombard our
planet
at a rate of between five and 30 per minute. They published the
results in the Oct. 1 Geophysical Research Letters. If
true, the
discovery would force a rethinking of the origins of the oceans,
terrestrial life and the formation of the solar system.
In five independent studies to be published Dec. 15,
scientists
including three teams from The University of Arizona conclude
that
theoretical calculations and observational evidence rule out the
small-comet hypothesis.
If the small-comet theory were correct, the Earth's sky would
be a
continual display of bright clouds and flashes, according to
calculations by Bashar Rizk and Alex J. Dessler of the UA Lunar
and
Planetary Laboratory. If 30,000 small comets bombard Earth daily,
as
the theory says, constant meteor-like displays would be visible
even
during the day.
The expanding cloud of tiny ice particles that small-comet
theory
suggests is created when a 30-ton, 40-foot-diameter comet breaks
up
high in the atmosphere would have a brightness somewhere between
that
of Venus and the full moon, Rizk and Dessler calculate.
(Dessler in
the late 1980s published a review of several earlier scientific
studies that rigorously tested small-comet theory.)
If, as small-comet theory says, a small comet strikes Earth
about
every three seconds, it would be visible for at least a
minute to
the naked eye, readily seen by anyone looking up, Rizk and
Dessler
add. "Where are they? We should see them," the LPL
researchers
puzzle.
"A whole-Earth flux of 20 comets per minute implies the
sudden
appearance of at least two bright patches of light every five
minutes," they report in GRL. "The two-hour
periods after sunset and
before sunrise ought to produce the most spectacular sightings
intermittent punctuations of bright, rapidly moving points of
light."
Twilight would be much more exciting in Tucson, Cairo, Sydney,
Capetown and other communities, say Rizk and Dessler.
Citizens of
Fairbanks, Montreal, Moscow and Stockholm would be treated to
near
all-night meteor shows, they add.
Small-comet theory requires that the bombarding comets were
formed in
very cold regions far the from sun, Timothy D. Swindle and David
A.
Kring of the LPL note in their paper. Comets that formed far out
in
space condensed from the same dust and gas that accreted into
planets, trapping "noble" gases in the same ratio as
the sun and the
rest of the solar system. Noble gases are inert, or non-reactive
gases, not easily removed from the atmosphere. They include
argon,
krypton, xenon, as well as the more common nitrogen, helium and
neon.
Swindle and Kring analyzed how much noble gas the small comets
would
have delivered to Earth's atmosphere over the lifetime of the
solar
system. "We know that if the Earth's atmosphere were
bombarded
according to small planet theory, it would have a dramatically
different composition," Kring said in an interview.
At the current rate of supposed small comet bombardment, Earth
should
have 500 times as much krypton and xenon and 30,000 times as much
argon in its atmosphere, Swindle and Kring calculate. Put another
way,
all the kypton and xenon in Earth's atmosphere would have been
delivered by small comets in 10 million years. All the
argon present
would have been added in 100,000 years. The scenario for Mars'
atmosphere is an even more enigmatic: Small comets would have
delivered the known martian inventory of krypton and xenon in 500
years and the known inventory of argon in about 60,000 years.
Either the rate of supposed small-comet bombardment is today
30,000
times greater than it has been over the 4.5-billion-year lifetime
of
the solar system, or the comets formed much nearer the sun, about
the
distance of Jupiter, for the theory to fit the observed noble gas
inventory, Swindle and Kring conclude. Comets can be
greatly depleted
in noble gases if they form closer to the sun, near Jupiter.
"The
problem with that idea is that it is completely inconsistent with
several other physical conditions that Frank's team require to
explain
other features of their hypothesis," Kring said in the
interview.
If the small-comet hypothesis is right, a small comet hits the
moon
at a rate of almost one per minute, Jennifer A. Grier and Alfred
S.
McEwen of the UA Lunar and Planetary Laboratory report in their
paper. That is, scientists should see evidence of 400,000 comet
hits
on the moon annually.
Even a small, low-density comet would excavate a crater at
least 50
meters in diameter and spread bright ejecta over an area of at
least
150 meters in diameter, Grier and McEwen calculate. (The
lunar
surface darkens over time; the underlying, unexposed soil is
lighter
in color.)
Grier and McEwen compared Apollo 17 images taken in late 1972
to
Clementine images taken 22 years later for a 52,000
square-kilometer
area of the moon, which is about half the size of Kentucky and
more
than one-tenth of one percent of the lunar surface. Any
crater and
bright spot seen in the 1994 Clementine images but not visible in
the
1972 Apollo photos might record a small impactor hit.
Each of the 3,920 bright spots seen over the study area in
1994 by
the Clementine spacecraft was also recorded by Apollo. If the
small-comet theory were correct, Clementine imaging should have
discovered more than 10,000 new bright impact spots over this
area.
Grier and McEwen calculate from the spacecraft observations an
upper
limit of 33 impacts a year for the entire moon, not 400,000 hits
per
year as expected according to the small-comet hypothesis.
Small
comets with properties hypothesized by Frank's team are probably
more
than a billion times less abundant than predicted, Grier and
McEwen
further conclude.
In another research article published in the Dec. 15
Geophysical
Review Letters, a team of researchers who use a Polar spacecraft
camera similar to the Frank team's Visible Imaging System also
report
seeing the dark pixels, or black points, that Frank interprets as
evidence for small comets. This team, however, concludes the dark
pixels are an inherent camera feature, or "noise"
rather than real
features.
A fifth paper in the journal suggests meteorites
as small as 50
centimeters in diameter create plumes of atmospheric gas that
Frank
and his team interpret as small comets. The large- scale analogy
to
this phenomenon is the Comet Shoemaker-Levy impacts on Jupiter,
they
report.
**********************************************
This document is distributed by UA NEWS SERVICES. News releases
and
other information about the UA are available at the News Services
WWW
site: http://www.opi.arizona.edu
**********************************************
Office of University Communication
Case Western Reserve University
Cleveland, OH
Contact: Susan Griffith, 216-368-1004, sbg4@po.cwru.edu
12/4/97
MARTIAN METEORITE CONTAINS NO BIOLOGICAL LIFE, RESEARCH TEAM SAYS
December 4 Nature article offers point-counterpoint approach to controversy
The famous Martian meteorite, ALH84001, contains no biological
life forms,
according to a Case Western Reserve University researcher and
colleagues.
The team issues this report in the December 4 issue of Nature,
duplicating
the methods of a team of scientists from the Johnson Space Center
and
Stanford University. In rare counterpoint writings in the
"Scientific
Correspondence" section, Nature allowed the Johnson Space
Center team to
respond to the group's findings. This paper also appears in the
December 4
issue.
CWRU's Ralph Harvey, senior research associate in the
Department of
Geological Sciences, was on the research team. The lead
researcher on
the paper was John Bradley from MVA Inc. and the School of
Material
Science and Engineering at Georgia Institute of Technology. The
third
researcher is Hap McSween from the University of Tennessee.
The trio reports that most of the purported nanofossils or
"worm-like
images" are nothing more than lamellae, or fractured
surfaces of pyroxene
and carbonate crystals.
Last year, the Johnson-Stanford team announced it found
evidence of
nanofossils in the meteorite. Reports of life on Mars spurred the
July 4
mission to Mars to look for further evidence of life.
Allan Hills 84001 -- a meteorite the size of a potato --
remains in the
center of a spirited controversy about the possibility of life on
Mars. The
meteorite was found in the 1980s in Antarctica by the National
Science
Foundation's Antarctic Search for Meteorite Program (ANSMET),
headed by
Harvey with headquarters at CWRU.
A Web page offers details on ANSMET, including a link to more
information on
the meteorite. To view these resources, visit
http://www.cwru.edu/artsci/geol/ansmet/index.html.
Harvey, who is currently on his annual expedition to
Antarctica to collect
meteorites, commented before leaving November 21 that the
Johnson- Stanford
team has always argued that they had used different techniques to
study the
meteorite.
Bradley, Harvey, and McSween published a paper last year in
Geochimica
et Cosmochimica Acta (GCA), announcing that what the other
researchers
observed was formed geologically, not biologically. The
Johnson-Stanford
group also announced that these nanofossils were lying on the
surface of the
meteorite.
In the first GCA study, which used transmission electron
microscope
imagining (TEM), the researchers found non-biological magnetite
whiskers on
or near the surfaces of the carbonates. Superficially the
whiskers look like
worms, but in fact they have nothing to do with biological
processes,
according to Harvey and colleagues.
The latest study took place over the past six months as the
researchers
re-examined the meteorite using the new techniques. This time
they found yet
another population of worm-like forms that are actually mineral
lamellae
formed by non-biological, geological processes. The lamellae look
like worms
or nanofossils, but when the specimen is tilted and viewed from
another
angle, it clearly shows that the lamellae are attached and part
of the
mineral surfaces.
"The surface topography is highly irregular on a
nanometre scale, with
emergent lamellae following the major cleavage direction of the
substrate,"
Bradley writes in the paper. The researchers have published
pictures of the
TEM images to support their findings.
"Peculiar surface structures or segmentation on the
worm-like forms are
artifacts from conductive metal coatings applied to the samples
for imaging
in the electron microscope. This is not the first time metal
coating
artifacts have lead to misidentification of nanofossils in
rocks," Bradley
said.
"We have now found two different types of mineral forms
in ALH84001
that look just like nanofossils, but they are strictly
non-biological
origins. Sometimes even nature has a perverse sense of
humor," he added.
Harvey stressed that during this latest study, the team was
careful to use
exactly the same methods as the Johnson-Stanford group to lay to
rest any
arguments that the research methods had affected the findings.
The worm-like mineral lamellae are commonly found at the
fractured
surfaces of planar crystals. Harvey noted that lunar rocks -- in
which there
has been no evidence of life found -- contain these same
formations.
Does this put an end to the life on Mars debate? "We
haven't driven the
final nail in the coffin yet about organisms in this Martian
rock, but our
latest article offers a lot of insight that shows these fractures
zones in
the rock are incredibly complex," Harvey said, "and
that it is very
dangerous to try to draw any hypothesis from a few pictures from
here or
there."