The shadowed regions of PSRs have been found to be even stranger than scientists had thought. In the shadows, what will we discover?
Robinson is the lead scientist for the robotic mission. The thing is cool.
There is water, water, everywhere.
Harold Urey was the first to theorize about the existence of PSRs. There may be depressions on which the sun doesn't shine near its poles. The moon is at a mere 1.5 degree tilt compared to Earth's 23.5 degree tilt. The sun strikes its poles almost horizontally, and the polar craters block light from reaching their depths. The lack of atmosphere on the moon meant that any ice in these sunless locations would have been quickly lost.
There was a theory that ice could persist inside PSRs. The moon's nighttime temperature was known to plunge to minus 150 degrees Celsius, meaning ice would get trapped in the cold. The permanently shaded areas of the moon should still be covered in ice.
The existence of ice at Mercury's poles was thought to have been caused by shadowed craters. Scientists detected an enhanced signal over the moon's south pole in 1994 that was consistent with water ice. There was a hunt going on.
Jean-Luc Margot and colleagues at Cornell University discovered that PSRs on the moon could contain ice. They made maps of the lunar poles using a radar dish in the desert. The regions that were permanently shadowed were identified using our maps.
Subsequent studies have identified thousands of PSRs, even though they only found a few. The deepest crater in the world is the Shackleton crater at the lunar south pole, which is twice as deep as the Grand Canyon. The smallest span is less than a hundredth of a millimeter. At the lunar and planetary science conference held in Houston in March, a planetary scientist at NASA presented research suggesting that some PSRs may grow and shrink as temperatures on the moon fluctuate. The cold regions are very dynamic. "They are moving forward."
Patrick O'Brien, a graduate student at the University of Arizona, presented evidence for the idea that some craters have double shadowed regions. The reflected light from the crater can cause ice to melt. Secondary craters inside PSRs don't get reflected light, so they are double shadowed. O'Brien said that the temperatures can be even colder than the shadows.
There arecy secrets.
The regions are so cold that carbon dioxide and nitrogen could be frozen there. The chemical composition of these and of the water ice inside PSRs could show how water got to the moon. Margaret Landis is a planetary scientist at the University of Colorado Boulder. She wanted to know when and how the conditions were favorable for life on Earth. The moon is a museum of the solar system's history and its ice is thought to have stayed mostly untouched since it arrived.
Some people think that water got to the moon. It arrived via impacts from asteroids or comets. When the solar system formed, water in the hot inner solar system was destroyed by the solar wind and only water in the frigid outskirts could accumulate into ice. Water was delivered to the inner solar system by these bodies. The second theory is that volcanic eruptions on the moon created a thin, temporary lunar atmosphere that caused ice to form at the poles. The hydrogen could have been taken to the moon by the solar wind.
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