FOR RELEASE: THURSDAY, JUNE 5, 1997, 4 P.M. EDT
Contact: Larry Bernard
Office: (607) 255-3651
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ITHACA, N.Y. -- Detailed radar images of the north and south poles of the
moon show no evidence of ice in areas of permanent shadow that are
observable with earth-based radars, researchers said today (June 6).
The data appear to contradict the conclusions of scientists, based on data
from the Clementine spacecraft and reported in the journal Science (29
November 1996), that there may be ice deposits at the South Pole of the
moon.
"We don't see anything that suggests ice. We don't think there is any
obvious evidence from the Arecibo radar images for the presence of
water-ice at the poles of the moon," said Donald B. Campbell, Cornell
University professor of astronomy and associate director of the National
Astronomy and Ionosphere Center (NAIC), which operates the Arecibo
Observatory under a cooperative agreement with the National Science
Foundation (NSF).
The observations, taken at Arecibo Observatory in Puerto Rico in 1992 and
released in the journal Science this week (6 June 1997), do indicate a
number of small areas less than a half-square-mile in size throughout the
polar regions whose radar reflection could be interpreted as ice. However,
some of these features occur in areas near the poles that are sunlit and
similar features are seen in radar images taken of clearly sunlit areas
much closer to the moon's equator. It is much more likely that their radar
reflection properties are due to very rough surfaces associated with the
steep slopes of impact craters than with ice deposits, the researchers said.
The Arecibo work was done by Nicholas J. S. Stacy, a former Cornell
graduate student now at the Defense Science and Technology Organization,
Australia; Campbell and Peter G. Ford, a principal research scientist at
the Center for Space Research at the Massachusetts Institute of Technology.
The studies initially constituted Stacy's thesis for a Cornell doctoral
degree, which he received in 1993. The researchers have presented their
findings at several of scientific conferences since then.
Researchers analyzing Clementine data suggested that ice deposits may cover
an area totaling 90 to 135 square kilometers (35 to 50 square miles) at the
south pole of the moon.
But, "We see no real evidence for anything like that," Campbell said,
adding that the Arecibo data studied the moon polar regions at the same
radio wavelength -- 13 centimeters -- as Clementine and at a similar
viewing angle, but with a resolution of 125 meters, or 400 feet, much
greater than the resolution used in the Clementine studies.
It is thought that areas of the moon in permanent shadow from the sun, at
the north and south poles, would be cold enough to harbor frozen water over
geologic time. There have been suggestions for more than 30 years that ice
may be found at the lunar poles.
In 1991 radar observations of Mercury using the NASA/JPL Goldstone antenna
and the Arecibo telescope found unusual radar reflections from the bottom
of several impact craters in that planet's polar regions. These
reflections are thought to indicate the presence of water ice. The Mercury
results provided a strong incentive to do high-resolution radar imaging of
the lunar poles.
"We were hoping to see a similar situation for the moon, with unambiguous,
bright spots at the poles," Campbell said. "With Mercury it's pretty
clear. But with the moon we didn't see anything like that. Our contention
is that the surface roughness is a much better candidate for the signatures
we're seeing. However, neither Arecibo nor Clementine observed all the
areas that are in permanent shadow and there is still the possibility that
there are ice deposits in the bottoms of deep craters."
The studies were funded by the National Science Foundation (NSF) and NASA.
Arecibo Observatory, which recently completed a $27 million upgrade that
will be dedicated on June 14, is operated by Cornell University's National
Astronomy and Ionosphere Center under a cooperative agreement with the NSF.
It is the world's largest single dish radio telescope, with a 1,000-foot
antenna and, when combined with a new one-megawatt transmitter, forms the
world's most powerful radar.
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