Moon Craters Could Be Coldest Place in Solar System
This image shows daytime (left) and nighttime lunar temperatures in Kelvin recorded by the Diviner instrument on NASA's Lunar Reconnaissance Orbiter in new images released Sept. 17, 2009.
Credit: NASA/UCLA

The coldest place in the solar system might be closer to home than we thought.

New data from NASA's Lunar Reconnaissance Orbiter (LRO) suggests that permanently shadowed craters at the moon's south pole might be colder even than Pluto and the other objects in the solar system's furthest most reaches.

In its first set of measurements, announced Thursday, LRO's Diviner Lunar Radiometer Experiment, which is conducting the first global survey of the temperature of the lunar surface, found that craters along the lunar south pole that have areas permanently shielded from the sun's light (and suspected to harbor deposits of water ice) have extremely cold temperatures.

"Diviner has recorded minimum daytime brightness temperatures in portions of these craters of less than -397 degrees Fahrenheit," said David Paige, Diviner's principal investigator and a UCLA professor of planetary science. "These super-cold brightness temperatures are, to our knowledge, among the lowest that have been measured anywhere in the solar system, including the surface of Pluto."

While it may seem odd that the moon, which is much closer to the sun, could be colder than Pluto, it's not at all unexpected, one planetary scientist said. In fact, the poles of Mercury may be even colder.

"The key point is not their distance from the sun, but the fact that there are regions at the poles of the Moon and Mercury that never see the sun, and so never get heated by sunlight," said Alan Boss, of the Carnegie Institution in Washington, D.C.

"The only heat they receive is from the underlying rock, but that means only interior heat leftover from their formation or their internal radioactive decays, but in any case the local rocks are still cold because they too are free to radiate out to -263 Celsius space without getting any heat back from the sun," Boss told SPACE.com.

The news of these frigid temperatures bolsters the idea that these craters could harbor water ice, which would be a boon to any future moon bases, which could melt the water and use it for drinking, or extract hydrogen for fuel.

The ultra-low temperatures of these craters are the opposite of those at the lunar equator, which are hotter than the boiling point of water at noontime.

Lunar surface temperatures are expected to change with the seasons, and Diviner will continue to monitor and map them throughout LRO's planned one-year mission.

LRO was launched on June 18, along with its companion, the Lunar Crater Observation and Sensing Satellite (LCROSS). LCROSS will impact one of these lunar craters, Cabeus A, on Oct. 9 to generate debris that can be analyzed for signs of water.