Who Killed Mars?
It's almost certain that Mars had an ocean-- but what happened? The last few hard science novels I've read suppose that Mars' lack of tectonic turnover -- all those extinct volcanoes-- contributed to any atmosphere bleeding off and liquid water evaporating or being frozen underground.
Now an article in Nature gives the case that Mars was slammed by an extinction-level asteroid that hit so hard, the planet's crust is lopsided-- as much as thirty klicks lower on one side. More than enough, if the computer modelling is right, to smear
any life off the surface and drive the Martian seas underground or into space. This gives one pause about the fragility of life on our own planet; maybe Americans ought to stop using words like "geek", "nerd" and "wonk" as insults and start begging the disdained technocrats to try and save save their sorry ass.
If the Martian ice caps aren't enough to sustain a green Mars, another asteroid story from Earth suggests an impact could have driven life underground. New Scientist reports that the 2 km wide asteroid that hit Chesapeake Bay drove cellular life more than a mile underground. I'm still holding out for Mole People.