So it occurred to me that all the "Venus was once like Earth" and "Mars was once like Earth" people are essentially wrong. Those never were ANYTHING like Earth. Namely, everything except Earth and Titan seems to be missing one thing almost entirely: Nitrogen.
Incidentally, this would also explain why Mars has such a thin atmosphere. Because it should be able to hold onto N2 just fine... if it had any to start with. As I was saying, Titan holds a thick atmosphere of N2 at lower gravity than Mars.
The problem with N2 vs O2 is one that doesn't even have anything to do with having a magnetic field. O2 is broken into atomic oxygen by just UV light from the sun, and then it either reacts with something or escapes into space. The same gravity that would allow you to hold onto O2, is nowhere near enough to hold the half weight of just O atoms. N2 is holding together much tighter, and needs higher frequency UV to break apart. The sun isn't producing very much of those frequencies, at its current temperature, and even less of it in the distant past when it was a cool young star.
This also ties in with the old terraforming thread, btw: yeah, well, just bringing water to Mars won't really cut it. We'd need to bring N2 from somewhere, ideally. And we have no real idea where.
This also has strong implications for life. We had some news recently about Phosphorous being rare in other nebulas. But Nitrogen is even more essential for anything even vaguely resembling life, as well as for holding onto your atmosphere, and down here having any seems to be an exception.
And I would say it has a pretty strong implication that Venus never was like Earth. We just never had nearly as much carbon in the atmosphere to start with, so I'm betting that Venus started its runaway greenhouse transformation long before Earth, and long before it could have any chance at a life that could give it an O2 atmosphere.
So anyway, this all gets me wondering: so where is all the Nitrogen? Just one planet and one moon in the whole solar system having any quantities worth talking about is making them rather an odd exception. What happened to N2 in other places? Or didn't they have any to start with? Probably didn't. But then where did WE get ours?
Incidentally, this would also explain why Mars has such a thin atmosphere. Because it should be able to hold onto N2 just fine... if it had any to start with. As I was saying, Titan holds a thick atmosphere of N2 at lower gravity than Mars.
The problem with N2 vs O2 is one that doesn't even have anything to do with having a magnetic field. O2 is broken into atomic oxygen by just UV light from the sun, and then it either reacts with something or escapes into space. The same gravity that would allow you to hold onto O2, is nowhere near enough to hold the half weight of just O atoms. N2 is holding together much tighter, and needs higher frequency UV to break apart. The sun isn't producing very much of those frequencies, at its current temperature, and even less of it in the distant past when it was a cool young star.
This also ties in with the old terraforming thread, btw: yeah, well, just bringing water to Mars won't really cut it. We'd need to bring N2 from somewhere, ideally. And we have no real idea where.
This also has strong implications for life. We had some news recently about Phosphorous being rare in other nebulas. But Nitrogen is even more essential for anything even vaguely resembling life, as well as for holding onto your atmosphere, and down here having any seems to be an exception.
And I would say it has a pretty strong implication that Venus never was like Earth. We just never had nearly as much carbon in the atmosphere to start with, so I'm betting that Venus started its runaway greenhouse transformation long before Earth, and long before it could have any chance at a life that could give it an O2 atmosphere.
So anyway, this all gets me wondering: so where is all the Nitrogen? Just one planet and one moon in the whole solar system having any quantities worth talking about is making them rather an odd exception. What happened to N2 in other places? Or didn't they have any to start with? Probably didn't. But then where did WE get ours?
via International Skeptics Forum http://bit.ly/2IRfYe0
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