[meteorite-list] MAVEN Reveals Speed of Solar Wind Stripping Martian Atmosphere

[Ron Baalke]

November 05, 2015

RELEASE 15-217

NASA Mission Reveals Speed of Solar Wind Stripping Martian Atmosphere 

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission has 
identified the process that appears to have played a key role in the 
transition of the Martian climate from an early, warm and wet environment 
that might have supported surface life to the cold, arid planet Mars is 
today.

MAVEN data have enabled researchers to determine the rate at which the 
Martian atmosphere currently is losing gas to space via stripping by the 
solar wind. The findings reveal that the erosion of Mars' atmosphere 
increases significantly during solar storms. The scientific results from the 
mission appear in the Nov. 5 issues of the journals Science and Geophysical 
Research Letters.

"Mars appears to have had a thick atmosphere warm enough to support liquid 
water which is a key ingredient and medium for life as we currently know 
it," said John Grunsfeld, astronaut and associate administrator for the 
NASA Science Mission Directorate in Washington. "Understanding what 
happened to the Mars' atmosphere will inform our knowledge of the dynamics 
and evolution of any planetary atmosphere. Learning what can cause changes to 
a planet's environment from one that could host microbes at the surface to 
one that doesn't is important to know, and is a key question that is being 
addressed in NASA's journey to Mars."

MAVEN measurements indicate that the solar wind strips away gas at a rate of 
about 100 grams (equivalent to roughly 1/4 pound) every second. "Like the 
theft of a few coins from a cash register every day, the loss becomes 
significant over time," said Bruce Jakosky, MAVEN principal investigator at 
the University of Colorado, Boulder. "We've seen that the atmospheric erosion 
increases significantly during solar storms, so we think the loss rate was 
much higher billions of years ago when the sun was young and more active."

In addition, a series of dramatic solar storms hit Mars' atmosphere in 
March 2015, and MAVEN found that the loss was accelerated. The combination of 
greater loss rates and increased solar storms in the past suggests that loss 
of atmosphere to space was likely a major process in changing the Martian 
climate.

The solar wind is a stream of particles, mainly protons and electrons, 
flowing from the sun's atmosphere at a speed of about one million miles per 
hour. The magnetic field carried by the solar wind as it flows past Mars can 
generate an electric field, much as a turbine on Earth can be used to 
generate electricity. This electric field accelerates electrically charged 
gas atoms, called ions, in Mars' upper atmosphere and shoots them into 
space.

MAVEN has been examining how solar wind and ultraviolet light strip gas from 
of the top of the planet's atmosphere. New results indicate that the loss is 
experienced in three different regions of the Red Planet: down the "tail," 
where the solar wind flows behind Mars, above the Martian poles in a "polar 
plume," and from an extended cloud of gas surrounding Mars. The science team 
determined that almost 75 percent of the escaping ions come from the tail 
region, and nearly 25 percent are from the plume region, with just a minor 
contribution from the extended cloud.

Ancient regions on Mars bear signs of abundant water - such as features 
resembling valleys carved by rivers and mineral deposits that only form in 
the presence of liquid water. These features have led scientists to think 
that billions of years ago, the atmosphere of Mars was much denser and warm 
enough to form rivers, lakes and perhaps even oceans of liquid water.

Recently, researchers using NASA's Mars Reconnaissance Orbiter observed the 
seasonal appearance of hydrated salts indicating briny liquid water on Mars. 
However, the current Martian atmosphere is far too cold and thin to 
support long-lived or extensive amounts of liquid water on the planet's 
surface.

"Solar-wind erosion is an important mechanism for atmospheric loss, and was 
important enough to account for significant change in the Martian climate," 
said Joe Grebowsky, MAVEN project scientist from NASA's Goddard Space 
Flight Center in Greenbelt, Maryland. "MAVEN also is studying other loss 
processes -- such as loss due to impact of ions or escape of hydrogen atoms 
-- and these will only increase the importance of atmospheric escape."

The goal of NASA's MAVEN mission, launched to Mars in November 2013, is to 
determine how much of the planet's atmosphere and water have been lost to 
space. It is the first such mission devoted to understanding how the sun 
might have influenced atmospheric changes on the Red Planet. MAVEN has been 
operating at Mars for just over a year and will complete its primary science 
mission on Nov. 16.

To view an animation simulating the loss of atmosphere and water on Mars:

http://svs.gsfc.nasa.gov/goto?4370

For more information and images on Mars? lost atmosphere, visit:

http://svs.gsfc.nasa.gov/goto?4393

For more information about NASA?s MAVEN mission, visit:

http://www.nasa.gov/maven

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