This image of Mars shows the north polar ice cap, the border between highlands and lowlands, former river valleys, plains covered by dark sands and the large Hellas Planitia impact basin in the south. Credit: ESA/DLR/FU Berlinjdippey t1_j9a9vy6 wrote
Reply to comment by _kempert in This image of Mars shows the north polar ice cap, the border between highlands and lowlands, former river valleys, plains covered by dark sands and the large Hellas Planitia impact basin in the south. Credit: ESA/DLR/FU Berlin by MistWeaver80
Is that true? I’m not aware of any planets lacking a magnetosphere that we’ve been able to actively observe losing an earth-like atmosphere to solar wind.
danielravennest t1_j9c1bpa wrote
The MAVEN spacecraft was sent to Mars to specifically measure the atmospheric loss rate. It is pretty low. The half-life of the Martian atmosphere is hundreds of millions of years. That's why it still has some atmosphere, and not vacuum.
jdippey t1_j9ch7m3 wrote
Can those results be extrapolated to a hypothetical Mars with an Earth-like atmosphere though? The atmospheric composition is quite different between Mars and Earth, after all.
danielravennest t1_j9fp3ni wrote
An Earth-like atmosphere would need to mass 27 tons per square meter on Mars vs 10 tons on Earth, due to the lower Martian gravity. That would be 3900 trillion tons total. Current loss rate is 95,000 tons a year. If the loss rate increased a thousand times to about 100 million tons/year. that still gives a half life of 20 million years, which is long by human standards.
There are several ways to reduce the losses. One is to put a magnetic shield "upwind" of the solar wind, and deflect it off the planet. That's effectively what Earth's magnetic field does.
Another is to dome the planet. Surface pressure depends on the weight of what is above the surface. It doesn't matter what that weight is made of. 27 tons is a lot per square meter. It would be more than 10 meters of glass thickness. So you can build a greenhouse the size of a planet and keep the atmosphere from leaking out.
Just because the top of an atmosphere being exposed to space is natural doesn't mean it is required. You can have several km of air below the dome to get an outdoor feeling, and leave the taller mountains sticking out into space if you want.
jdippey t1_j9fpimy wrote
Definitely interesting, but unfortunately I doubt we will ever get the point of turning mars into a habitable planet. If anything, I think we will just make habitable shelters.
Thanks for the explanation!
danielravennest t1_j9fryin wrote
WE won't do anything substantial to Mars. The Martians will, once there are millions of them, if they have enough desire for it.
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