Environmental Conditions of Early Mars given by an Energy Balance Model

Geological and morphological evidences show that liquid water or saline solution could have flowed on the Early Mars' surface, at the end of the Noachian (3.8 - 3.9 Gyr ago). However, while it is mostly thought that liquid water existed in the past, the environmental conditions such as the surface pressure and temperature of this period and their variation are not known. We use a one-dimensional energy balance model which includes meridional heat transport and greenhouse warming. We calculated the latitudinal temperature profiles for different orbital parameters and surface pressure values estimated from an atmospheric mass evolution model. The calculated surface pressure on Mars at the end of the Noachian are between 0.25 bar and 2 bars. Our model suggests that stable saline solutions, can exist on early Mars for surface pressures higher than 1.9 bar. For lower surface pressures, saline solutions can flow sporadically at high latitudes during high obliquity periods. Other sources of transient warming are then needed to allow presence of saline solution, such as sulfur outgassing by volcanism or transient warming by large impacts.