For any future astronauts who land on Mars, there is one piece of advice that shouldn’t even need to be said: keep your helmet on! Mars has an atmosphere, like Earth, but it is much thinner than ours (and mostly carbon dioxide), and so is unbreathable by humans. However, evidence has continued to grow that Mars’ atmosphere was once a lot thicker than it is now, early on in the planet’s history. Recent findings from the Curiosity rover have added to that evidence, as well as showing not only how Mars has lost most of the atmosphere that it once had, but also that the atmosphere which remains is still very active.
The new data was presented last Monday at the European Geosciences Union 2013 General Assembly in Vienna.
Most of Mars’ original atmosphere has leaked into space, a process that previous evidence has indicated, but is now also supported by analysis from the Sample Analysis at Mars (SAM) instrument on Curiosity. SAM has made very precise measurements of argon isotopes in the Martian atmosphere; these isotopes are variants of the same argon molecule which have different atomic weights. Currently, the atmosphere contains four times the amount of a lighter stable isotope (argon-36) than a heavier one (argon-38). The original ratio of argon in the early solar system was much higher than it is now, so the lower ratio on Mars indicates that most of the lighter argon isotope has been lost over time.
“We found arguably the clearest and most robust signature of atmospheric loss on Mars,” said Sushil Atreya, a SAM co-investigator at the University of Michigan, Ann Arbor.
Despite the atmosphere now being much thinner, Curiosity has found that it is still quite dynamic. Measurements have shown differing humidity in various locations along the path that the rover has traveled so far. The daily air temperature has also gradually climbed since when Curiosity first landed last August, as winter has turned into spring and then summer. The daily highs have been up to about 0˚C (34 ˚F) and the lows about -70 ˚C (-94 ˚F). While plunging at night and in winter, daytime temperatures, especially in the summer, can be relatively comfortable by earthly standards.
Of course, it has already been long known that the Martian atmosphere, despite now being so much less dense than Earth’s, can still put on a good show. Strong winds can create global dust storms. Huge dust devils leave their tracks on the ground and have been photographed in action by the Spirit and Opportunity rovers. Smaller whirlwinds have also been detected by Curiosity, although they didn’t raise enough dust to be seen directly. The Phoenix lander also observed snow falling over its landing site near the north pole, fog has been seen in canyons and wispy clouds have been seen both from orbit and from the ground.
Thanks to these and other observations by various orbiters, landers, and rovers, we now have a much better idea of what Mars used to be like—a world with a much thicker atmosphere, rain, rivers, lakes, and maybe even oceans. A lot has changed since then, but at least in terms of its atmosphere, the Red Planet is still very much alive.
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