Looking in the wrong places for water on the moon?

[Savwafair2012 Profile]

Water is turning up in unexpected places on the moon, controversial new observations suggest.

According to theory, water is not stable on the moon's surface above -167 °C. As a result, ice should be concentrated in "cold traps" near the lunar poles, in craters that never get any sunlight. NASA's LCROSS spacecraft found water when it crashed into one such crater, called Cabeus, in October.

But new observations from the Lunar Reconnaissance Orbiter (LRO) suggest that many of the permanently shadowed regions near the south pole are dry and several potentially wet regions are sunlit.

The observations come from the Lunar Exploration Neutron Detector (LEND) experiment, which looks for possible water deposits by measuring neutrons emitted from the moon. Water or other hydrogen-bearing compounds reduce the number of fast neutrons.

LEND examined 37 permanently shadowed craters near the south pole and found that only three of them – Cabeus, Faustini, and Shoemaker – showed significant amounts of hydrogen. Several illuminated regions also appear to be hydrogen rich.

"I think we have a paradigm-busting set of observations here," says Jim Garvin, the chief scientist at NASA's Goddard Space Flight Center.

Targeted search
LEND's principal scientist, Igor Mitrofanov of the Russian Space Research Institute, reported these "neutron suppressed regions" last week at the American Geophysical Union meeting in San Francisco.

He believes that a half-metre-thick layer of dry soil may cover a layer of dirty ice, preventing the ice from evaporating into space. He and his colleagues calculate that the icy layer, which may have been delivered to the moon by asteroids or comets, could contain concentrations of water as high as 3 to 5 per cent.

However, the new results remain controversial. The LEND instrument contains a new feature that is designed to improve its focus, so that it only picks up neutrons from a small patch of ground below it. But it has not been tested on a planetary mission before, and some researchers suspect it may be detecting neutrons from surrounding regions as well.

"There are a lot of questions about the instrument response that need to be answered," says Rick Elphic of NASA Ames Research Center. "The jury's still out on the validity of what they are claiming to see."

Fortunately, LRO is expected to continue gathering data for two more years, and LEND's results will grow more accurate over time. "I think our story will be a lot sharper by next summer," Garvin says.