An artist's impression of Mars' atmosphere escaping, via Wiki Commons
Curiosity arrived on Mars last August ready to answer a number of nagging science questions. One big question is finally getting some answers: What happened to Mars's atmosphere? The latest data returned from the rover suggest that the bulk of the Martian atmosphere floated off into space long ago, and that the planet’s current atmosphere is just a wispy remnant.When it comes to the Martian atmosphere, Curiosity’s main tool is its Sample Analysis at Mars (SAM) instrument. SAM sniffs the air and measures the ratio of gasses. In a recent sniff, SAM measured the ratio of two isotopes of the noble gas argon, and found something interesting. The lighter and more stable isotope argon-36 is about four times as common as the heavier isotope argon-38.
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It may seem minor, but it’s actually a noteworthy result. It’s the clearest evidence scientists have gathered to support the widely held theory that Mars’s atmosphere has escaped over time. It seems that the current atmosphere of Mars, which is only about one percent as thick as the Earth’s, is merely a shell of its former self.
Curiosity's picture of the holes it drilled to make some of its recent atmospheric measurements. Via NASA
This latest result has soothed some decades old uncertainties about the argon ratio measured in 1976 by NASA's Viking landers and from the small volumes of the gas extracted from Martian meteorites. But more interestingly it says a lot of Mars as a young planet. The argon ratio SAM found is much lower than the solar system's original ratio that scientists have determined based on argon-isotope measurements of the sun and Jupiter. So what does this mean for ancient Mars? Likely that Mars has long favored losing lighter isotopes over heavier ones.The ratio of argon levels aren’t the only interesting bit of atmospheric science to come back from the red planet. Curiosity can measure a host of atmospheric variables with its Rover Environmental Monitoring Station (REMS). One interesting thing the Spanish-made instrument has found is that while the daily air temperature has climbed steadily over the last eight months, the change has nothing to do with the rover’s location. Humidity on the other hand changes dramatically depending on the rover’s location. That in itself if pretty interesting since Curiosity hasn’t exactly gone that far on a global scale.
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An annotated schematic explaining how water vapor moves in Mars's
There’s also Curiosity's laser-shooting Chemistry and Camera instrument, ChemCam. This has turned up some interesting results on the dust that gives Mars its distinctive red color. Scientists have known for a while that Mars is red because of the iron oxides in the dust, but the recent ChemCam measurements have revealed just how chemically complex the dust is.It’s not just dust, it’s got traces of hydrogen that could be in the form of hydroxyl groups or water molecules. Studying the possible interchange of water molecules between the atmosphere and the ground falls under the domain of other instruments on the rover, namely the Russian-made Dynamic Albedo of Neutrons (DAN) instrument.That is sort of the big news from Mars we’re going to get for a while. Curiosity is gearing up for its version of spring break, a forced two week break in communications while the Sun passes between the Earth and Mars. Since these alignments happen every 26 months, the Curiosity team are prepared.For the next little while the rover will run surface tests and carry out a backlogs of commands that have been uploaded over the last month. Once communications are reestablished, the rover will get back to drilling Martian rocks in the name of science.
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