Re:What happened to it? (Score 4, Informative)

I realize I could easily look it up. But, what is the leading theory as to why the planet can no longer sustain liquid water. I know that in it's current condition with low gravity and lack of atmosphere it cannot sustain liquid water... But was Mars once larger?

Runaway atmosphere loss is a leading candidate due to a lack of a magnetic field (and those missing gigatons of rock)...