Patrick Barry may be no Leigh Brackett, but he nonetheless tells a tale of planetary woe:
Once upon a time — roughly four billion years ago — Mars was warm and wet, much like Earth. Liquid water flowed on the Martian surface in long rivers that emptied into shallow seas. A thick atmosphere blanketed the planet and kept it warm. Living microbes might have even arisen, some scientists believe, starting Mars down the path toward becoming a second life-filled planet next door to our own.But that’s not how things turned out.
Mars today is bitter cold and bone dry. The rivers and seas are long gone. Its atmosphere is thin and wispy, and if Martian microbes still exist, they’re probably eking out a meager existence somewhere beneath the dusty Martian soil.
Somehow Mars lost its CO2-rich atmosphere, and NASA is sending its MAVEN mission there to examine the flow of CO2 and other molecules from Mars into space:
Conventional wisdom holds that Mars’s atmosphere is vulnerable because the planet lacks a global magnetic field. Earth’s magnetic field stretches far out into space and envelopes the whole planet in a protective bubble that deflects the solar wind. Mars has only regional, patchy magnetic fields that cover relatively small areas of the planet, mostly in the southern hemisphere. The rest of the atmosphere is fully exposed to the solar wind. So the loss could be caused by the slow erosion of the atmosphere in these exposed areas.David Brain of UC Berkeley has proposed another, seemingly contrary possibility. These small magnetic fields might actually hasten the loss of Mars’s atmosphere, Brain suggests.
The solar wind might buffet those magnetic field lines, occasionally pinching off a “bubble” of field lines that then drifts off into space — carrying a large chunk of the atmosphere with it. If so, having a partial magnetic field might be worse than having none at all.
(Hat tip to Nyrath.)