Here’s a SETI Institute seminar by Stephen Brecht on the question of what happened to the water believed once to have covered significant portions of Mars: Attempts to explain water loss from Mars – SETI Institute

From the video caption:

The debate about whether or not Mars ever had life upon it centers on the issue of water.

Was there water on Mars? If so, where has it gone? One of the explanations for the water loss focuses on the idea that the solar wind is removing the water by acceleration ionospheric ions and removing them from Mars.

The problem is complicated by a variety of features: the presence of crustal magnetic fields on the surface of Mars, the photo-chemistry taking place in Mars’ atmosphere/ionosphere, and the solar activity (EUV flux and solar wind behavior), and finally the small size of Mars. These features make for a very non-linear interaction which in many regions has little to do with fluid dynamics but rather plasma kinetics.

In this talk a discussion of these issues as well as results of kinetic plasma simulations with data comparisons will be presented. Dr. Brecht will also discuss how the results from the ongoing MAVEN mission at Mars can be used to test the presented plasma simulation predictions.