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Project Progress

Permanent ground ice can exist indefinitely beneath a dry surface that has no frost, not even seasonally. A paper by Schorghofer, Phys. Rev. E 75, 041201 (2007) provides insight into this phenomenon, and finds that ancient ice is only expected in the presence of large temperature variations. The study is relevant to high mid-latitude ice on Mars and to the Dry Valleys of Antarctica.

Another component of this project studies the dynamics of ice sheets on Mars. Terrestrial Ice Ages were discovered in the 19th century and the advancement and retreat of ice is caused by astronomical influences, such as changes in Earth’s orbit around the sun. In the past few years, it was discovered that Ice Ages also occurred on Mars, and now it emerges how these cycles actually work on Mars.

Previous theories described how ice is lost from the polar caps and deposited at equatorial regions during a past climate epoch, and later the equatorial ice is redistributed by the atmospheric circulation to the high mid-latitude areas where ice is still found today. This occurred probably around 4-5 million years ago. A letter to Nature (doi: 10.1038/nature06082) describes what must have happened to this ice as the rotation axis of Mars continued to wobble over the last few million years. Surface temperature and atmospheric humidity changed considerably, because of changing patterns of solar illumination. When the climate was dry, the ice receded to greater depth or disappeared entirely except at the highest latitudes. During a humid climate period, atmospheric vapor freezes inside the porous soil to form ice. This cycle of retreat and formation repeated many times. Today we are left with two kinds of ground ice: an old massive ice sheet and very recent pore-ice. We expect to see both when the Phoenix Lander arrives on Mars in 2008.

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