Letter

Nature 449, 192-194 (13 September 2007) | doi:10.1038/nature06082; Received 10 February 2007; Accepted 3 July 2007

Dynamics of ice ages on Mars

Norbert Schorghofer1

  1. Institute for Astronomy and NASA Astrobiology Institute, 2680 Woodlawn Drive, University of Hawaii, Honolulu, Hawaii 96822, USA

Correspondence to: Norbert Schorghofer1 Correspondence and requests for materials should be addressed to the author (Email: norbert@hawaii.edu).

Unlike Earth, where astronomical climate forcing is comparatively small, Mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale1, 2, 3, 4, 5, 6. The geographic extent of the subsurface ice found poleward of approximately plusminus60° latitude on both hemispheres of Mars7, 8, 9 coincides with the areas where ice is stable7, 10, 11. However, the tilt of Mars' rotation axis (obliquity) changed considerably in the past several million years. Earlier work3, 12 has shown that regions of ice stability, which are defined by temperature and atmospheric humidity, differed in the recent past from today's, and subsurface ice is expected to retreat quickly when unstable11, 12, 13. Here I explain how the subsurface ice sheets could have evolved to the state in which we see them today. Simulations of the retreat and growth of ground ice as a result of sublimation loss and recharge reveal forty major ice ages over the past five million years. Today, this gives rise to pore ice at mid-latitudes and a three-layered depth distribution in the high latitudes of, from top to bottom, a dry layer, pore ice, and a massive ice sheet. Combined, these layers provide enough ice to be compatible with existing neutron and gamma-ray measurements7, 8, 9.

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