What turned Mars from the warm, wet planet that space scientists believe it was in the distant past into the cold, dessicated world of today? NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) is providing part of the answer, as it measures how fast the Martian atmosphere is being lost today. According to the space agency, the culprit is the solar winds, which are slowly stripping away the atmosphere of the Red Planet atom by atom at a rate of roughly 100 gm (3.5 oz) per second and even more during solar storms.
By gathering data on the interaction of the solar wind and ultraviolet light on the upper Martian atmosphere, MAVEN is helping scientists gain a better understanding of how and where the planet's atmosphere is being stripped away. According to NASA, 75 percent of the loss occurs at the "tail" of the planet as the solar wind flows around it, while nearly 25 percent flows out from a polar plume, and a small loss occurs in the extended cloud of gas around Mars.
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This loss is caused by the constant blowing of the solar winds – a stream of subatomic particles flowing out from the Sun and carrying its magnetic field along with such force that its influence can reach out for billions of miles. As these winds and the magnetic field flow over Mars, the result is like a dynamo and generates an electric field. This causes gas ions in the upper reaches of the Martian atmosphere to accelerate and blow away into interplanetary space.
In addition, MAVEN data from a recent solar storm in March indicates that the loss rate accelerates during such events. NASA says that since storms were more common in the past, it was a major factor in the loss of the Martian atmosphere.
"Like the theft of a few coins from a cash register every day, the loss becomes significant over time," says 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."
Launched in November 2013 from Cape Canaveral, Florida, MAVEN arrived at Mars on September 21, 2014 on a mission to study the Martian atmosphere, its mechanisms, and why the atmosphere is slowly escaping into space. The orbiter's first observations included taking ultraviolet images of the tenuous oxygen, hydrogen, and carbon coronas in the planet's upper atmosphere, and creating a comprehensive map of its ozone layers. The orbiter is scheduled to finish its primary science mission on November 16.
"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," says John Grunsfeld, astronaut and associate administrator for the NASA Science Mission Directorate. "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."
The video below shows how the solar winds interact with the Martian atmosphere.