MAVEN findings reveal how Mars' atmosphere was lost to space

MAVEN, which stands for Mars Atmosphere and Volatile Evolution Mission, is a NASA space probe created to study the atmosphere of Mars while it orbits the Red Planet.

"We're in the process of tallying up what the total amount removed was, but I'm going to guess right now that the amount of atmosphere that was present was about as thick as the Earth's atmosphere - about one or two bars of gas", said Bruce Jakosky from the University of Colorado in Boulder, US.

MAVEN team members had previously announced measurements showing that atmospheric gas was being lost to space and that described the processes by which atmosphere was being stripped away.

The scientists used the two isotope's relative abundance at Mars' surface and upper atmosphere to estimate how much of the atmospheric gas had been lost to space.

This evidence suggests that the Red Planet's climate was very different a long time ago - probably warm enough for water to flow on the surface for extremely long periods.

"This discovery is a significant step toward unraveling the mystery of Mars' past environments", MAVEN scientists Elsayed Talaat said in the university statement.

A dramatic type of change the Context Camera has documented more than 200 times is a fresh impact crater appearing between the times of two observations.

There are many ways a planet can lose some of its atmosphere. Theories have included that reactions with rocks at the surface locked up gases in the ground, or that solar radiation blasted the atmosphere away over time.

The lighter one blows away more easily on solar winds, leaving the atmosphere with a greater proportion of the heavier isotope.

And, the effect likely dominated the planet's climate and habitability.

The researchers say it's possible microbial life could've existed on Mars' surface in the early days, but as the planet cooled that life may have been "driven underground or forced into occasional or rare surface oases". Since the lighter isotope of argon escapes more readily, over time the concentration of the heavier isotope of argon builds up.

As a "noble gas", argon cannot react chemically with anything; the only process that can remove it to space is a physical process called "sputtering" by the solar wind. In the sputtering process, ions picked up by the solar wind can physically knock atmospheric gas into outer space.

The team then used its measurements of argon loss to determine the amount of oxygen atoms that had also been knocked into space through sputtering.

They focused on carbon dioxide because it is the greenhouse gas which can keep in heat and keep the planet warm.

'We determined that the majority of the planet's Carbon dioxide was also lost to space by sputtering, ' said Jakosky.

'There are other processes that can remove Carbon dioxide, so this gives the minimum amount of Carbon dioxide that's been lost to space'.

Using data gathered by the MAVEN's Neutral Gas and Ion Mass Spectrometer instrument, NASA's Sample Analysis at Mars, and the Curiosity rover, scientists estimated how much gas had disappeared.

"Because the two isotopes have quite similar masses, these measurements are not easy to do", said Yelle, adding that NASA's Viking probes, whose landings in 1976 marked the first touchdown of a man-made object on Mars, were not able to make those measurements.

'The combined measurements enable a better determination of how much Martian argon has been lost to space over billions of years, ' said Paul Mahaffy of NASA's Goddard Space Flight Center. "Using measurements from both spacecraft points to the value of having multiple spacecraft that measure complementary things".

Jakosky was lead author in an article - "Mars" atmospheric history derived from upper-atmosphere measurements of Ar/Ar' - which was published in the journal Science today (31 March, 2017).

  • Carolyn Briggs