How Mars' atmosphere got so thin: New insights from Curiosity

July 18, 2013
NASA's Curiosity rover used the Mars Hand Lens Imager (MAHLI) to capture this set of 55 high-resolution images, which were stitched together to create this full-color self-portrait. Credit: NASA/JPL-Caltech/Malin Space Science Systems

( —New findings from NASA's Curiosity rover provide clues to how Mars lost its original atmosphere, which scientists believe was much thicker than the one left today.

"The beauty of these measurements lies in the fact that these are the first really high-precision measurements of the composition of Mars' ," said Sushil Atreya, professor of atmospheric, oceanic and space sciences at the University of Michigan.

Atreya is co-author of two related papers published in the July 19 issue of Science, and co-investigator on Curiosity's Sample Analysis at Mars (SAM) suite of instruments, considered the rover's cornerstone lab.

SAM measured the abundances of different gases and isotopes in samples of Martian air, according to NASA. Isotopes are variations of the same chemical element that contain different numbers of , such as the most common , carbon-12, and a heavier , carbon-13, which contains an additional neutron.

SAM analyzed the ratios of heavier to lighter isotopes of carbon and oxygen in the carbon dioxide that makes up most of Mars' atmosphere today. Measurements showed that heavy and oxygen were more abundant in today's thin atmosphere compared with the proportions in the raw material that formed the planet (which scientists can deduce from proportions in the sun and other parts of the solar system.) This provides not only supportive evidence for the loss of much of Mars' original atmosphere, but also gives clues to how the loss occurred. It suggests that the planet's atmosphere escaped from the top, rather than due to the lower atmosphere interacting with the ground, NASA's web story states.

"The isotope data are unambiguous and robust, having been independently confirmed by the quadrupole mass spectrometer and the tunable laser spectrometer, two of the SAM suite instruments," Atreya said. "These data are clear evidence of a substantially more massive atmosphere, hence a warmer, wetter Mars in the past than the cold, arid planet we find today."

Curiosity landed inside Mars' Gale Crater on Aug. 6, 2012, Universal Time.

Explore further: Michigan scientists bring special expertise to new rover mission

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1.6 / 5 (13) Jul 19, 2013
Life supports the atmosphere and the atmosphere supports life.
Hot metals in contact with water causes it to disassociate into H and O. If life is not there to use the energy available in recombining the water, eventually the H2 wonders off into space. No water and no atmosphere and no life.
4.5 Billion years ago the sun was too weak to keep the Earth liquid. This preserved the water as Ice until life established itself around geothermal vents in the deep oceans.
Once life was established it recombined the liberated hydrogen and the sun increased it's temperature 20%.
We (Gaia) are now flirting with the inner edge of the Goldilocks Zone. And then we discovered the carbon that we have been sequestering in order to compensate for the increased output of the sun.
This 10 to 1 conversion of carbon into food has allowed us to double the Ape population every 35 years.
5 / 5 (4) Jul 19, 2013
Perhaps the very weak magnetic field allowed the solar radiation to boil off the atmosphere
3.7 / 5 (3) Jul 19, 2013
CaptainSlog: That's been the consensus for years now, although we're just now getting the isotope measurements to confirm it. The leading alternative is that giant impacts, such as the one that formed the Hellas basin, blew the air into space. Of course, there's no reason that both couldn't have occurred.

Solar wind blow-off selectively depletes lower mass elements, and lower mass isotopes withing elements. That's what Curiosity found. Impacts would remove everything more or less equally, which would be a good way to remove heavier gases, such as molecular nitrogen.

Egleton: Solar UV also breaks down water, so hot metals and life aren't required.
1.7 / 5 (6) Jul 19, 2013
Not only the weak magnetic field, but the low gravity allows the atmosphere to escape into space.
5 / 5 (1) Jul 20, 2013
Yes, that's also a major factor. Light molecules travel faster than heavy ones, at the same temperature, so any planet loses light elements quicker. But any molecule exceeding escape velocity will be lost. Earth can pretty well hold nitrogen and oxygen, even in atomic form, but Mars loses the single atoms.
1.5 / 5 (8) Jul 21, 2013
Marrs is a shit hole.
1.9 / 5 (9) Jul 21, 2013
Perhaps the very weak magnetic field allowed the solar radiation to boil off the atmosphere

I thought that theory was already widely accepted. Why are they making this sound like a new revelation/discovery?
5 / 5 (1) Jul 21, 2013
Solar radiation isn't affected much by the magnetic field, as the major radiation loss is from UV splitting water. The magnetic field has a major impact on loss from the solar wind, and solar wind blowoff is the main loss route for nitrogen and oxygen. In extreme cases, and the early solar wind was much stronger than today's, it can remove gases that would be stable looking only at temperature and escape velocity.

That seems to be what happened to Venus. It may have been able to hold water, if it had been at Earth's distance, but being closer, the solar wind was denser, and basically collapsed the magnetic field into the atmosphere. Earth, a little farther out, and a little larger, could maintain a field wide enough to largely protect its air from "blowoff". Mars didn't have a chance, even at its distance, due to its smaller and weaker field.

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