Early MAVEN Results Offer Clues Of What Depleted The Atmosphere of Mars

NASA's Goddard Space Flight Center

NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter entered into Martian orbit in September and began its primary science mission in mid-November. The goal of the mission is to learn why the atmosphere of Mars depleted, which is a large factor in why the planet is no longer able to support liquid water. Some of the earliest science results that were returned have indicated that solar wind may have punched holes in the lower atmosphere of Mars, which could have helped contribute to the depletion of the atmosphere. The results were presented by MAVEN principal investigator Bruce Jakosky on December 14th at the fall meeting of the American Geophysical Union.

The particles associated with solar wind are typically deflected by a planet’s ionosphere, which is a layer of the upper atmosphere that has been charged by solar radiation and shields the planet. However, this method of protection diminished after the planet’s core cooled, and stopped moving in order to generate the magnetic field. As MAVEN dipped down into the ionosphere to take readings, its Solar Wind Ion Analyzer discovered streams of particles associated with solar wind that existed much lower into the atmosphere than was expected.

“We are beginning to see the links in a chain that begins with solar-driven processes acting on gas in the upper atmosphere and leads to atmospheric loss,” Jakosky said in a press release. “Over the course of the full mission, we’ll be able to fill in this picture and really understand the processes by which the atmosphere changed over time.”

It appears that while charged particles are deflected by the ionosphere, neutral particles are able to go much deeper. Unfortunately, these neutral particles can become charged within the lower regions of the ionosphere. These newly-charged particles act just like ordinary solar wind, and are capable of inflicting damage in the atmosphere as they punch their way out. Understanding how these particles are able to sneak into lower altitudes and become recharged will help scientists to explore if other layers of the atmosphere are affected in this way.

Though the solar wind is contributing to the loss of the upper atmosphere, the lower atmosphere is responsible for climate, including the former responsibility of keeping the planet warm enough to sustain liquid water. MAVEN is utilizing the Neutral Gas and Ion Mass Spectrometer in order to see if the lower atmosphere has been affected by solar wind activity and if gas in the lower atmosphere is “leaking” into the upper atmosphere.

MAVEN’s Suprathermal and Thermal Ion Composition (STATIC) instrument has detected ions leaving the Martian atmosphere. After they travel through the ionosphere, they have to bust back out through the shield meant to reflect them. Ultimately, many particles push through this layer at once, erupting out of the atmosphere, and leaving behind a hole. Over time, the measurements by STATIC will help determine the rate at which the atmosphere is being depleted.

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