RELATED: Colonizing Mars Might Require Humans to Radically Alter Their Bodies and Minds
Argon is a stable “noble gas” and the only process that can remove it to space is a physical process called “sputtering” where atoms are physically knocked away from the atmosphere due to impacts from energetic particles from the Sun, called solar wind.
The researchers used argon gas measurements to determine the amount of other gases that would have been lost by the same mechanism. Their findings suggest that Mars' atmosphere was probably once as thick as Earth's, but made primarily of carbon dioxide. But that thicker, life-giving atmosphere has since been lost, leading to huge changes to the Red Planet's climate since its formation.
Earth’s atmosphere and magnetic field protects our planet from the effects of solar wind. Mars, too, once had a strong magnetic field, produced by a dynamo effect from its interior heat. But as the smaller planet cooled, Mars lost its magnetic field. Jakosky and the MAVEN team tie the magnetic field loss to the atmospheric loss on Mars.
“The evidence points to Mars having had a magnetic field early in its history, but then the field shutting off around 4.1 billion years ago,” Jakosky said in an email. “The magnetic field would have caused the solar wind to stand off from the atmosphere, as it does on Earth, and thereby protect the atmosphere. I suspect that it was the turn-off of the magnetic field that allowed the turn-on of stripping of the atmosphere by the solar wind.”