Mars' Missing Air Might Just be Hiding Options

[Guest_AlexBlackwell_*]

Mars' Missing Air Might Just be Hiding
By Ker Than
Staff Writer, Space.com
posted: 25 January 2007
02:01 pm ET

This refers to the Barabash et al. paper ("Martian Atmospheric Erosion Rates") being published in the January 26, 2007, issue of Science.

[NMRguy]

I guess I come from a slightly different science background, but I have serious problems when authors state "These rates can be propagated backward over a period of 3.5 billion years". How well have they constrained the numbers presented in the article--I don't see any error bars on the numbers in the abstract? (I'm at home, so I don't have access to the article.)

Details of the exact model seem lacking, and my initial reaction was very similar to that of ElkGroveDan.


In terms of bulk properties of Mars, I don't think you need a substantially higher fraction of volatiles to account for the lower the bulk density. Evidence supports that Mars underwent a high degree of differentiation after accretion. Iron and other metals sunk to the center, silicates rose to the mantle, and the volatiles made their way to the surface. And Mars’ bulk density is not much greater than the silicates (olivine-rich) in our own mantle. Include a smaller core with generous amounts of sulfur and you have a very plausible scenario.

But I don’t expect the volatiles in Mars’ crust to have any noticeable effect on the total density. You would need to move farther away from the sun for that.

[Guest_AlexBlackwell_*]

I guess I come from a slightly different science background, but I have serious problems when authors state "These rates can be propagated backward over a period of 3.5 billion years". How well have they constrained the numbers presented in the article--I don't see any error bars on the numbers in the abstract? (I'm at home, so I don't have access to the article.)

In the paper, Barabash et al. state: "Propagating the measured rates backward in time, one can estimate the total amount of carbon dioxide and water, ΔM(CO2) and ΔM(H2O), lost through this particular channel [i.e., solar wind interaction] over 3.5 gigayears (Gy)." They refer the reader to the Supporting Online Material for the paper, which, I believe, is freely available to non-subscribers. See page 3 under the heading Total escape over the planetary history for a more thorough explanation of their methodology.