Fw: Cornell News: No ice found at lunar poles (fwd from ljk4@msn.com)

Eugen Leitl eugen at leitl.org
Wed Nov 12 11:40:33 PST 2003


----- Forwarded message from LARRY KLAES <ljk4 at msn.com> -----

From: "LARRY KLAES" <ljk4 at msn.com>
Date: Wed, 12 Nov 2003 13:20:47 -0500
To: "europa" <europa at klx.com>
Cc: "BioAstro" <bioastro at setileague.org>
Subject: Fw: Cornell News:  No ice found at lunar poles
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----- Original Message -----
From: cunews at cornell.edu
Sent: Wednesday, November 12, 2003 1:15 PM
To: CUNEWS-PHYSICAL_SCIENCE-L at cornell.edu; CUNEWS-SCIENCE-L at cornell.edu
Subject: Cornell News: No ice found at lunar poles

Arecibo radar shows no evidence of thick ice at lunar poles, despite
data from previous spacecraft probes, researchers say

EMBARGOED  UNTIL  WEDNESDAY, NOV. 12, 2003, AT 1 P.M. EST

Contact:  David Brand
Office:  607-255-3651
E-mail:  deb27 at cornell.edu


ARECIBO, P.R.  --  Despite evidence from two space probes in the 
1990s, radar astronomers say they can find no signs of thick ice at 
the moon's poles. If there is water at the lunar poles, the 
researchers say, it is widely scattered and permanently frozen inside 
the dust layers, something akin to terrestrial permafrost.

Using the 70-centimeter (cm)-wavelength radar system at the National 
Science Foundation's (NSF) Arecibo Observatory, Puerto Rico, the 
research group sent signals deeper into the lunar polar surface -- 
more than five meters (about 5.5 yards) -- than ever before at this 
spatial resolution. "If there is ice at the poles, the only way left 
to test it is to go there directly and melt a small volume around the 
dust and look for water with a mass spectrometer," says Bruce 
Campbell of the Center for Earth and Planetary Studies at the 
Smithsonian Institution.

Campbell is the lead author of an article, "Long-Wavelength Radar 
Probing of the Lunar Poles," in the Nov. 13, 2003, issue of the 
journal Nature. His collaborators on the latest radar probe of the 
moon were Donald Campbell, professor of astronomy at Cornell 
University; J.F. Chandler of Smithsonian Astrophysical Observatory; 
and Alice Hine, Mike Nolan and Phil Perillat of the Arecibo 
Observatory, which is managed by the National Astronomy and 
Ionosphere Center at Cornell for the NSF.

Suggestions of lunar ice first came in 1996 when radio data from the 
Clementine spacecraft gave some indications of the presence of ice on 
the wall of a crater at the moon's south pole. Then, neutron 
spectrometer data from the Lunar Prospector spacecraft, launched in 
1998, indicated the presence of hydrogen, and by inference, water, at 
a depth of about a meter at the lunar poles. But radar probes by the 
12-cm-wavelength radar at Arecibo showed no evidence of thick ice at 
depths of up to a meter.  "Lunar Prospector had found significant 
concentrations of hydrogen at the lunar poles equivalent to water ice 
at concentrations of a few percent of the lunar soil," says Donald 
Campbell. "There have been suggestions that it may be in the form of 
thick deposits of ice at some depth, but this new data from Arecibo 
makes that unlikely."

Says Bruce Campbell, "There are no places that we have looked at with 
any of these wavelengths where you see that kind of signature."

The Nature paper notes that if ice does exist at the lunar poles it 
would be considerably different from "the thick, coherent layers of 
ice observed in shadowed craters on Mercury," found in Arecibo radar 
imaging. "On Mercury what you see are quite thick deposits on the 
order of a meter or more buried by, at most, a shallow layer of dust. 
That's the scenario we were trying to nail down for the moon," says 
Bruce Campbell. The difference between Mercury and the moon, the 
researchers say, could be due to the lower average rate of comets 
striking the lunar surface, to recent comet impacts on Mercury or to 
a more rapid loss of ice on the moon.

What makes the lunar poles good cold traps for water is a temperature 
of minus 173 degrees Celsius (minus 280 degrees Fahrenheit). The limb 
of the sun rises only about two degrees above the horizon at the 
lunar poles so that sunlight never penetrates into deep craters, and 
a person standing on the crater floor would never see the sun. The 
Arecibo radar probed the floors of two craters in permanent shadow at 
the lunar south pole, Shoemaker and Faustini, and, at the north pole, 
the floors of Hermite and several small craters within the large 
crater Peary. In contrast, Clementine focused on the sloping walls of 
Shackleton crater, whose floor can't be "seen" from Earth. "There is 
a debate on how to interpret data from a rough, tilted surface," says 
Bruce Campbell.

The Arecibo radar probe is a particularly good detector of thick ice 
because it takes advantage of a phenomenon known as "coherent 
backscatter." Radar waves can travel long distances without being 
absorbed in ice at temperatures well below freezing. Reflections from 
irregularities inside the ice produce a very strong radar echo. In 
contrast, lunar soil is much more absorptive and does not give as 
strong a radar echo.

Related World Wide Web sites:  The following sites provide 
additional information on this news release.  Some might not be part 
of the Cornell University community, and Cornell has no control over 
their content or availability.

o Arecibo Observatory: <http://www.naic.edu>

o Center for Earth and Planetary Studies: <http://www. 
nasm.si.edu/ceps/>

-30-



The web version of this release, with accompanying photos, may be 
found at 
http://www.news.cornell.edu/releases/Nov03/radar.moonpoles.deb.html
-- 

Cornell University News Service
Surge 3
Cornell University
Ithaca, NY 14853
607-255-4206
cunews at cornell.edu
http://www.news.cornell.edu
----- End forwarded message -----
-- Eugen* Leitl <a href="http://leitl.org">leitl</a>
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