New MAVEN findings reveal how Mars' atmosphere was lost to space

March 30, 2017, University of Colorado at Boulder
New results from the MAVEN mission reveal that substantial loss of atmosphere is what dramatically changed the climate of Mars. Credit: The Lunar and Planetary Institute NASA's MAVEN mission

Solar wind and radiation are responsible for stripping the Martian atmosphere, transforming Mars from a planet that could have supported life billions of years ago into a frigid desert world, according to new results from NASA's MAVEN (Mars Atmosphere and Volatile Evolution Mission) spacecraft led by the University of Colorado Boulder.

"We've determined that most of the gas ever present in the Mars atmosphere has been lost to space," said Bruce Jakosky, principal investigator for MAVEN and a professor at the Laboratory for Atmospheric and Space Physics (LASP). "The team made this determination from the latest result, which reveals that about 65 percent of the argon that was ever in the atmosphere has been lost to space."

Jakosky is lead author of a paper on this research to be published in Science on Friday. Marek Slipski, a LASP graduate student, co-authored the study.

MAVEN team members had previously announced measurements showing that was being lost to space and that described the processes by which atmosphere was being stripped away. The present analysis uses measurements of today's atmosphere to give the first estimate of how much gas has been removed through time.

Liquid water, essential for life, is not stable on Mars' surface today because the atmosphere is too cold and thin to support it. However, evidence such as features resembling dry riverbeds and minerals that only form in the presence of liquid water indicates the ancient Martian climate was much different - warm enough for water to flow on the surface for extended periods.

There are many ways a planet can lose some of its atmosphere. For example, chemical reactions can lock gas away in surface rocks or an atmosphere can be eroded by radiation and wind from the planet's parent star. The new result reveals that and radiation were responsible for most of the atmospheric loss on Mars and that the depletion was enough to transform the Martian climate. The solar wind is a thin stream of electrically conducting gas constantly blowing from the surface of the sun.

Young stars have far more intense ultraviolet radiation and winds, so atmospheric loss by these processes was likely much greater early in Mars' history, and these processes may have been the dominant ones controlling the planet's climate and habitability, according to the team. It's possible that microbial life could have existed at the surface early in Mars' history. As the planet cooled off and dried up, any life could have been driven underground or forced into occasional or rare surface oases.

Jakosky and his team got the result by measuring the atmospheric abundance of two different isotopes of argon gas. Isotopes are atoms of the same element with different masses. Because the lighter of the two isotopes escapes to space more readily, it will leave the gas remaining behind enriched in the heavier isotope. The team used this enrichment together with how it varied with altitude in the atmosphere to estimate what fraction of the atmospheric gas has been lost to space.

As a "noble gas" argon cannot react chemically with anything so it won't get sequestered in rocks, and the only process that can remove it to space is a physical process called "sputtering" by the solar wind. In sputtering, ions picked up by the solar wind impact Mars at high speeds and physically knock atmospheric gas into space. The team tracked argon because it can be removed only by sputtering. Once they determined the amount of argon lost by sputtering, they could use the efficiency of sputtering to determine the sputtering loss of other atoms and molecules, including carbon dioxide (CO2).

CO2 is of interest because it is the major constituent of Mars' atmosphere and because it's an efficient greenhouse gas that can retain heat and warm the planet.

"We determined that the majority of the planet's CO2 also has been lost to space by sputtering," said Jakosky. "There are other processes that can remove CO2, so this gives the minimum amount of CO2 that's been lost to space."

The team made its estimate using data on the Martian upper from MAVEN's Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument supported by measurements from the Martian surface made by NASA's Sample Analysis at Mars (SAM) instrument on board the Curiosity rover.

"The combined measurements enable a better determination of how much Martian argon has been lost to over billions of years," said Paul Mahaffy of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Mahaffy, a co-author of the paper, is principal investigator on the SAM instrument and lead on the NGIMS instrument, both of which were developed at NASA Goddard.

"Using measurements from both platforms points to the value of having multiple missions that make complementary measurements," said Mahaffy.

NASA Goddard manages the MAVEN project and MSL/Curiosity is managed by NASA's Jet Propulsion Laboratory in Pasadena, California.

Explore further: Sputtering: How mars may have lost its atmosphere

More information: "Mars' atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar," Science, science.sciencemag.org/cgi/doi … 1126/science.aai7721

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11 comments

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cantdrive85
1 / 5 (4) Mar 30, 2017
Now everyone remember, according to jonesdumb this is not sputtering, it's "sputtering"...
Anda
5 / 5 (1) Apr 01, 2017
Well, the details of this study are surely interesting, but the conclusions were already known.
Lately most articles are presented as if they'd made new discoveries.
Science doesn't need sensationalism...
markmknc
not rated yet Apr 02, 2017
What I am curious about, assuming that Earth had an atmosphere back when Mars apparently had one, and Earth is closer to Sol and therefore more susceptible to those same damaging solar winds, why are we here? Why does Earth still have an atmosphere when it should have been stripped away before Mars' atmosphere, based on this hypothesis anyway? Hmmmnnn, I need more before I am sold. Perhaps Earth's atmosphere has an extra protective layer, or more, than Mars' atmosphere had? How can we find out if Mars had an ozone layer?
Captain Stumpy
4 / 5 (4) Apr 02, 2017
Lately most articles are presented as if they'd made new discoveries
@Anda
i don't think i've ever read any studies about Martian atmosphere where they "quantify the amount of gas lost to space through time"

this is a direct measurement from MAVEN - so it is new, unless i missed a few missions where they already passed over this ground
Gases are being lost from the Mars atmosphere to space today [e.g., (1, 2)], potentially in quantities sufficient to change the planet's climate [e.g., (3)]. A goal of the Mars Atmosphere and Volatile Evolution (MAVEN) mission is to quantify the amount of gas lost to space through time (4, 5). Processes that strip gas to space preferentially remove the lighter of pairs of isotopes, leaving the remaining atmosphere enriched in the heavier isotope [e.g., (6)]. An observed heavy-isotope enrichment is a strong indicator that loss to space has occurred (3, 7).
gkam
1 / 5 (4) Apr 02, 2017
mark, Earth is much larger and has stronger gravity, but more important, has a still- active magnetic field to deflect the Solar Wind.
markmknc
5 / 5 (1) Apr 02, 2017
gkam, I get that, but the article stated that "... Mars... a planet that could have supported life billions of years ago...", so, with an atmosphere, doesn't that at least suggest that Mars also had an "active magnetic field"? And how much solar radiation does that magnetic field deflect compared to the ozone layer? If the magnetic field does enough, why are scientists so worried about the holes in the ozone layer allowing too much radiation through? Do you see where I was going with my initial questions? Because it was supposedly the radiations from the solar winds that blasted away much of the gas in Mars' atmosphere.
gkam
1 / 5 (4) Apr 02, 2017
marc, Mars is farther from the Sun but most important, smaller, which means it cooled down faster, stopping the movement of the iron core which made the magnetic field, ending the protection for the atmosphere.

Ozone, part of the upper atmosphere, protects us from another danger, hard ultraviolet light. It is depleted by atmospheric pollution with man-made chemicals, such as flurocarbons.

The magnetic field does its work farther out in space with charged particles, repelling most and collecting some at the poles.
Estevan57
5 / 5 (2) Apr 02, 2017
@markmknc Here is a link I believe will clarify the loss of magnetosphere, and subsequent loss of atmosphere on Mars.
Nice pictures too.

https://arstechni...y-world/
markmknc
5 / 5 (1) Apr 02, 2017
gkam, ok, I get it. But the dynamo theory is just that, still just a theory. It has not been proven to be the cause of the earth's magnetic field, as far as I know. Ok, done here, and thanks.

Estevan57, thanks for the link, I will look that up.
Captain Stumpy
5 / 5 (1) Apr 02, 2017
But the dynamo theory is just that, still just a theory
@markmknc
do not confuse colloquial definitions with scientific ones: to be a theory in science it has to "be repeatedly tested, using a predefined protocol of observations and experiments" (see: https://en.wikipe...c_theory )

the dynamo theory has a long history:
1956 - http://www.dtic.m...D0038699

1978 - http://www.igf.fu...er_s.pdf

2005 - https://arxiv.org...5052.pdf

or many more: https://scholar.g...as_sdtp=

Captain Stumpy
5 / 5 (1) Apr 02, 2017
It has not been proven to be the cause of the earth's magnetic field, as far as I know. Ok, done here...
@markmknc cont'd
something else that you may want to consider: https://ocw.mit.e...hscience

the site is free and has graduate level courses in everything from physics and math to psychology

i highly recommend getting involved and learning more about what interests you, specifically, and at least learning a bit more about the scientific method in general (see: https://en.wikipe...c_method )

the power of the scientific method is in the evidence presented and then validated

have fun and hope you get your answers

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