Is the Martian atmosphere pretty much as expected from the early data?
Sagan: Yes, the important findings are a few percent of both nitrogen and argon. The importance we give to the nitrogen is that if you want to imagine a microbiology in any way similar to the terrestrial sort, you have to have nitrogen in the atmosphere. But the main thing is the abundance of isotopes of argon and nitrogen – argon 36 and argon 40, and nitrogen 14 and nitrogen 15, which by two separate arguments give evidence for an early dense atmosphere on Mars. SB: It is less dense now because why? Sagan: A variety of reasons. The ones that I lean towards are the freezing out of the atmosphere in the polar caps. I think it very likely that the dense early atmosphere is still there, but it’s buried. SB: What’s the sunlight at high noon at the site of Vikings I and II versus sunlight at high noon in Pasadena? Sagan: Half. It’s like what you have here on an overcast day. SB: How does Mars compare with Venus? Sagan: Well, despite the good operation of the Soviet spacecraft on Venus it go
