Artist’s
rendering of a solar storm hitting Mars and stripping ions from the
planet's upper
atmosphere. Credits: NASA/GSFC
(November 6, 2015) 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.