Oct. 20, 2006 — Donald Campbell has some advice for colleagues debating where to send a robotic probe to look for water ice on the moon: don't expect much at the south pole.
High-resolution radar images taken by ground-based observatories of Shackleton crater, a 15-mile-wide pit on the moon's south pole, show no sign of thick water-ice deposits, says Campbell, a planetary scientist with Cornell University in New York.
That's not to say scientists planning to smash a pair of spacecraft into the moon's surface won't find small grains of ice mixed in the dust, added Campbell, lead author of a research paper published in this week's issue of the journal Nature.
Intrigued by long-standing theories that the moon's caps harbor ice deposits, Campbell and colleagues used the Arecibo Observatory in Puerto Rico and a second radar telescope in Green Bank, W. Va., to probe Shackleton crater in hopes of finding ice sheets similar to what has been found at Mercury's poles.
"It had been a reasonable suggestion since the 1960s that there were deposits of water ice," Campbell said, "but we didn't see anything that looks like that."
Campbell and his colleagues found the cause of radar echoes noted in previous studies which had led to speculation of lunar ice deposits. Instead of bouncing off ice, the radar reflected off small rocks that had been ejected during an asteroid or comet impact and the craggy walls of the crater's inner surface.
The findings were published as scientists wrapped up a meeting in California to discuss potential impact sites for a two-part robotic lunar probe. The spacecraft is scheduled to be launched along with NASA's Lunar Reconnaissance Orbiter in two years.
The Lunar Crater Observation and Sensing Satellite, known as LCROSS, consists of a pair of satellites designed to smash into the permanently shadowed floor of a lunar crater. The impacts are expected to send up a plume of material which will be analyzed by space- and ground-based observatories for signs of water vapor and other elements.
