Curiosity rover sees signs of vanishing Martian atmosphere

Before going incommunicado behind the Sun for a month, NASA’s Mars Curiosity rover sent Earth evidence that the Red Planet has lost much of its original atmosphere.

The findings, announced by Jet Propulsion Laboratory scientists at the European Geosciences Union meeting in Vienna, bolster the idea that the Martian atmosphere was once much thicker than it is today -- and come less than a month after the rover drilled its first rock and found signs that Mars was once hospitable to life.

Curiosity’s Sample Analysis at Mars instrument sniffed the Martian atmosphere and counted up the isotopes of argon in the air. Isotopes are heavier and lighter versions of the same element, and when a planet starts to lose its atmosphere, the lighter isotopes in the upper layers are the first to go. So if scientists see fewer of the lighter isotopes than expected, it might mean that there was once much more air there.

Photos: See Curiosity’s images from Mars

The researchers looked at two isotopes of argon: the heavier argon-38 and the lighter argon-36. They found that there was four times as much argon-36 as argon-38 -- a lower share of the lighter argon than expected based on data from other parts of the solar system.

Some of that missing argon-36 must have escaped because the top of the atmosphere had started to blow away, they surmised. This could mean Mars’ atmosphere was much thicker in the past than what Curiosity picks up today.

The scientists recently used this technique with carbon isotopes, finding similar results. But the new argon measurements provide much firmer evidence than older, less certain data on argon isotopes from the Viking mission in 1976, as well as from Martian meteorites.

Curiosity is experiencing what scientists call “solar conjunction,” when the sun comes between Earth and Mars, blocking communications until May. But Curiosity isn’t taking a vacation. The rover has to take weather and radiation measurements every day — part of a detailed list of chores sent by the Mars Science Laboratory team at JPL.

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