Solar Storms May Have Stripped Early Mars of its Atmosphere

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet's upper atmosphere. Credits: NASA/GSFC

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. Credits: NASA/GSFC

In 2013, NASA launched its MAVEN spacecraft on a mission to study one of the Red Planet’s greatest mysteries: how it lost its atmosphere some four billion years ago.

Mars and Earth shared similar features in their early days. The two planets were warm and wet, holding vast bodies of liquid water and a thick atmosphere. Some scientists even speculate that life could have first emerged on Mars, and then hitched a ride to Earth on a meteorite.

But while Earth remained habitable, eventually spawning a tangled web of complex life, the conditions on Mars quickly deteriorated. The lakes, rivers, and global ocean all but vanished, aside for some water locked away in the polar ice caps and seasonal streaks of liquid brine. Meanwhile the atmosphere thinned down to a sliver (less than 1% of Earth’s), leaving the Red Planet a cold, dry, and barren world.

Understanding the story of Mars’ atmosphere may yield clues to the potential for life in Mars’ past, but also to whether the same thing could one day happen to Earth.

NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has been collecting data since 2014. This week NASA announced new insight into the process that may have led to Mars’ demise.

“Quoting Bob Dylan: ‘The answer, my friend, is blowin’ in the wind,’” said Michael Meyer, the lead scientist of NASA’s Mars Exploration Program. The results are published in the Nov. 5 issues of the journals Science and Geophysical Research Letters.

Lost to the Solar Wind

The solar wind is a stream of charged particles that flows from the Sun at a speed of a million miles per hour. That wind interacts with the upper atmosphere of planets, stripping away ions and gases like oxygen and carbon dioxide into space.

In March of 2015, the sun launched a bubble of energized plasma traveling at about 2 million miles per hour toward Mars. Credit: NASA Goddard Space Flight Center

In March of 2015, the sun launched a bubble of energized plasma traveling at about 2 million miles per hour toward Mars. Credit: NASA Goddard Space Flight Center

Using MAVEN data, researchers have determined that Mars is currently losing about 100 grams (roughly 1/4 pound) of atmosphere every second, which isn’t a particularly large amount. However, the rate of escape increases significantly during solar storms.

In March 2015, the Martian atmosphere was hit by a series of dramatic solar flares. MAVEN data revealed that atmospheric escape rates went up by a factor 10 to 20 during the event.

The sun was much more active and the solar wind much more intense during early Mars’ history. This suggests that solar storms may have played a key role in stripping Mars of its protective atmosphere, turning the Red Planet into a dry and barren land billions of years ago.

Martian Magnetism

Earth didn’t share the same fate, however, because its global magnetic field protects its atmosphere from the solar wind. Mars once had a global magnetic field, too, a protective shield generated by the internal dynamo in its molten core—until that dynamo died around four billion years ago.

There are a few theories for why this happened. One says that Mars simply got cold because of its size, much like the Moon, and so its core shut down. Another theory involves large asteroid impacts, which would have warmed the planet’s outer layer, hence shutting down the heat flow between core and mantle needed to drive the dynamo.

In 2016, NASA will send a new lander to Mars, named InSight (for Interior exploration using Seismic Investigations, Geodesy and Heat Transport), which will investigate the planet’s deep interior and possibly offer new clues about the story of Mars’ magnetism.

MAVEN data also revealed a new kind of aurora in Mars’ northern hemisphere, one similar to Earth’s Northern Lights. But while this type of aurora on Earth is driven by magnetism of the poles, Mars’ aurora may be driven by the remnant magnetic field of the crust, the researchers suspect.

In the end, MAVEN is filling up important gaps in our understanding of Mars’ history and its potential for past or present life—a knowledge that’s invaluable as NASA is preparing to send humans on a journey to the Red Planet.