The Moon's South
Pole: Very High Resolution, Radar Images Find Rocks Abundant, But No Ice
Sheets
(18 October 2006) Using the highest
resolution radar-signal images ever made of the moon - images from the National
Science Foundation's (NSF) Arecibo Telescope in Arecibo, P.R., and the NSF's
Robert C. Byrd Telescope in Green Bank, W.Va. - planetary astronomers have
found no evidence for ice in craters at the lunar south
pole.
Cornell University, Smithsonian Institution and Australian
scientists report the findings in the latest Nature (Oct. 19,
2006).
"These new results do not preclude ice being present as small
grains in the lunar soil based on the Lunar Prospector's discovery of enhanced
hydrogen concentrations at the lunar poles," said Donald Campbell, Cornell
professor of astronomy and a principal investigator. "There is always the
possibility that concentrated deposits exist in a few of the shadowed locations
not visible to radars on Earth, but any current planning for landers or bases
at the lunar poles should not count on this."
This radar image of the south pole region of the moon is about 250 km by 100 km. Shackleton crater (A) is 19 km in diameter. The Lunar Prospector orbiter impacted Shoemaker crater (B), 51 km in diameter. The south pole is about on the center of the left rim of Shackleton. The image was made in April 2005 by transmitting from Arecibo Observatory in Puerto Rico at 13 cm wavelength and receiving the radar echo with the Robert C. Byrd Green Bank Telescope in West Virginia. The underlying resolution of the image is about 20 m, the highest resolution radar image ever made of the moon. (courtesy: D. Campbell (Cornell), B. Campbell (Smithsonian) and L. Carter (Smithsonian))
Echoes from radar signals transmitted to the
moon from the giant Arecibo telescope were received at the Green Bank
telescope. These echoes allowed scientists from Cornell, the Smithsonian
Institution and the Defence Science and Technology Organization in Australia to
create images, offering the best view ever of the shadowed terrain at the lunar
south pole.
Since the 1960s, theories have suggested that ice may exist
deep inside impact craters in permanent shadow from the sun, where temperatures
on the moon's surface do not exceed minus 280 degrees Fahrenheit (or minus 173
Centigrade), at the poles. The theory was bolstered in 1992 when Earth-based
radar telescopes located "ice deposits" inside impact craters at the poles of
the planet Mercury.
The Lunar Prospector orbiter discovered
concentrations of hydrogen at the moon's poles. If this hydrogen were in the
form of water molecules - still a subject of debate - then it would correspond
to an average of 1 to 2 percent of water ice in the lunar soil in the shadowed
terrain.
However, Earth-based radar measurements since the 1990s have
consistently failed to detect ice deposits similar to those on Mercury. Since
water ice would be a significant resource for any future lunar base, many of
the instruments on NASA's 2008 Lunar Reconnaissance Orbiter/Lunar Crater
Observation and Sensing Satellite mission seek to learn if water ice is present
in permanently shadowed craters.
Even in the lunar summer at the south
pole, the sun barely edges above the horizon, thus the bottom impact craters
never see the sun. Because of the tilt of the moon's orbital plane relative to
the Earth's equatorial plane, the Earth can rise much higher above the horizon
at the lunar south pole than the sun, so telescopes on the Earth can "see" some
of the shadowed area. However, since that area is permanently in shadow, only
radar can image that terrain.
Donald Campbell and Jean-Luc Margot of
Cornell University, Bruce Campbell and Lynn Carter of the Smithsonian
Institution, and Nicholas Stacy of the Australian Defence Science and
Technology Organization conducted the research. Cornell's National Astronomy
and Ionosphere Center manages the Arecibo telescope, and the Green Bank
Telescope is part of the National Radio Astronomy Observatory, which is
operated by Associated Universities Inc. for the NSF.
(source: Cornell
University)