Atmospheric Loss to Space and the History of Water on Mars

摘要

Mars is the nearest planet that potentially harbors life and that can be explored by humans, so its history of water is of considerable importance. Water was abundant on early Mars but disappeared as Mars became the cold, dry planet we see today. Loss of water to space played a major role in the history of this water. Variability of components of the atmosphere that can drive escape has taken place on all timescales, from interannual to the 10(5)-, 10(6)-, and >10(7)-year timescales of obliquity variations to the 4 billion-year timescale of large-scale climate evolution. These variations have had a major impact on the behavior of the atmosphere, climate, and water. They also make it difficult to evaluate quantitatively where the water has gone. Despite this uncertainty, the observed enrichment in the ratio of deuterium/hydrogen requires that loss to space has been substantial.