Evidence for climate change on Mars

Lewis, Stephen R. and Read, Peter L. (2006). Evidence for climate change on Mars. In: Blondel, Phillippe and Mason, John eds. Solar System Update. Springer Praxis Books: Geophysical Sciences. Springer and Praxis Books, pp. 135–158.

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One of the most striking differences between the present day climates of Earth and Mars is the ubiquitous and abundant presence of liquid water on Earth and the extremely dry atmosphere and surface of Mars. Features on the surface of Mars, discovered by early spacecraft missions in the 1970s and apparently caused by flowing water on the surface in the past, have lead to much speculation concerning the early Martian climate and the possibility that the planet was once relatively warm and wet. Such speculation is fuelled by the search for life on Mars, either in the present or as a fossil record. Until recent missions, however, there has been little direct evidence for the existence of large water deposits, other than in the form of ice, largely around the northern polar cap. During the past 2 years, however, NASA’s Mars Odyssey and ESA’s Mars Express spacecraft have discovered evidence for considerable amounts of ice lying at relatively shallow depths in the Martian regolith. The NASA Mars Rovers have also found considerable in situ evidence for ancient water in the nearby rocks and landscape.

It still seems unclear, despite various attempts to model the ancient Martian climate, whether Mars had a sustained warm, wet climate, with liquid water flowing on the surface, or whether it has remained mostly in a frozen state, interrupted by occasional melting events for short periods of time. Climate change on more recent timescales (10^4–10^6 years BP) has perhaps been less dramatic, but more amenable to systematic modelling. There is strong evidence of changes in Mars’ climate on these timescales in the polar-layered deposits, associated with the obliquity cycle, and Mars GCMs have started to make progress in modelling climate change associated with varying astronomical parameters. We will briefly review such studies as well as the limited observational evidence for more dramatic climate change since the early epochs of the planet’s history.

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