MARS EARLY CLIMATE AND THE PRESENCE OF WATER

Evidence for the presence of liquid water early in Mars' history continues to accumulate. Some of the most recent evidence for pervasive liquid water includes the discovery of sulfate and gypsum layers by the Mars Exploration Rovers and Mars Express. Furthermore, increasingly detailed images of the martain surface have revealed richly dendritic channels, suggesting periodic surface runoff with rates exceeding several cm per day. While the idea of a warm and wet early Mars has been a paradigm generally accepted since the first channels where observed over thirty years ago, the idea itself has had its periods of freeze and drought. These inclement periods have often been brought on by new observations, for example the presence of large olivine layers at the surface, which suggested long periods of exceedingly dry conditions, or difficulties in resolving the observations with the theoretical expectations of the early martian climate. The early sun was most likely approximately 75% fainter than it is today. About 65-70 degrees of greenhouse warming is needed to bring surface temperatures to the melting point of water. To date climate models have had a difficult time producing a continuously warm and wet early Mars. This may be a good thing, as it appears the morphological and mineralogical evidence suggests a more complicated history of climate and water throughout Mars' past. From warm and wet to cold and dry, Mars climate and the state of its water has been a roller coaster ride.