Karela Fry

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A romance of the martian atmosphere

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Two papers published together in Science, one by Webster and friends, the other by Mahaffy and friends, find something exciting about the early history of Mars. Apparently, the Martian atmosphere started out similar to the Earth’s, but some catastrophic event about 4 billion years ago stripped Mars of its air and water.

How does data collected by the Curiosity rover on Mars tell us so much? A nice explanation is given in a podcast on Science. Here is a summary from the transcript:

Interviewer – Linda Poon
Okay. And from my understanding, the lighter isotope escapes, and that’s how you guys are using that as evidence of Mars atmospheric loss?

Interviewee – Christopher Webster
Yes, that’s exactly right. If you look at carbon, for example, most of carbon has a mass of 12, but one in every 100 atoms has a mass of 13. This is an isotope of carbon. So in carbon dioxide, there’s a small amount of carbon dioxide that’s carbon-13. And it should be in the normal ratio like we find on Earth, but on Mars, we see because, as you said the lower mass escapes more easily, we see this enrichment, if you like, in the heavier carbon-13. [Our new measurements] tell us they’re in the proportion that we see in the meteorites. And that’s very important because we believe that certain meteorites are from Mars.

Interviewer – Linda Poon
And then you also measured the deuterium-to-hydrogen ratio, and you found evidence for
two-stage evolution for martian water. Can you tell us a little about both the measurement and these two stages?

Interviewee – Christopher Webster
[The] deuterium-to-hydrogen ratio, [is] a simple measurement for identifying the origin of planets and the evolution of the solar system. It tells us where Earth’s water came from. It’s believed to have come from cometary and asteroid input or delivery, if you like, of water to Earth. And all that story is wrapped up in this D/H ratio that we look at of many planets. On Mars, it’s a special case, because the escape removes the lighter hydrogen. You’re left with a heavier deuterium, so it’s very high in its D/H ratio. Our results support the idea of the significant, early loss a long time ago and then a small loss over the last three to four billion years. We looked at the D/H; we saw very high values. And then we’re now looking at that same ratio in the dust and the rocks of Mars, and we’re seeing very different values in those. So again, we have this tremendous capability to tie the history of water on Mars. We know it had a watery past. Now we can map out how that water evolved with time and was lost and how it interacts with the atmosphere in the escape process.


Written by Arhopala Bazaloides

July 19, 2013 at 9:07 pm

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