NASA’s MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft has observed three phenomena in the atmosphere of Mars: a polar plume of escaping atmospheric particles, a layer of metal particles high in its atmosphere and aurora that reaches deep into the atmosphere.
Map of MAVEN’s auroral detections in December 2014 overlaid on the surface of Mars: the map shows that the aurora was widespread in the northern hemisphere, not tied to any geographic location. Image credit: University of Colorado.
Atoms in the upper atmosphere of the Red Planet become electrically charged ions after being energized by solar and space radiation. Because they are electrically charged, these ions feel the magnetic and electric forces of the solar wind.
The solar wind and more violent solar activity have the ability to strip away ions from the upper atmosphere through electric and magnetic forces generated by a variety of mechanisms, causing the atmosphere to become thinner over time.
The goal of MAVEN, the first mission devoted to understanding the Martian upper atmosphere, is to determine the role that loss of atmospheric gas to space played in changing the Martian climate through time.
MAVEN was launched on November 18, 2013 from Cape Canaveral Air Force Station in Florida, and entered Mars’ orbit on September 21, 2014.
The probe is in its science mapping orbit and has been taking data since the start of its primary mission on November 16, 2014. The furthest point in the spacecraft’s elliptical orbit has been 4,039 miles (6,500 km) and the closest 81 miles (130 km) above the surface.
“The spacecraft and instruments continue to work well, and we’re building up a picture of the structure and composition of the upper atmosphere, of the processes that control its behavior, and of how loss of gas to space occurs,” said MAVEN’s principal investigator Dr Bruce Jakosky of the University of Colorado.
“MAVEN is observing a polar plume of escaping atmospheric particles,” he added. “The amount of material escaping by this route could make it a major player in the loss of gas to space.”
Theoretical models had predicted that the electric field generated by the incoming solar wind could drive ions in the direction of one pole or the other, creating a polar plume of escaping ions.
“When tracing particle trajectories in the models, the plume looks a bit like a Mohawk,” said MAVEN team member Dr David Brain of the University of Colorado.
The spacecraft has also detected a long-lived layer in the electrically charged upper atmosphere of Mars made up of metal ions – iron and magnesium – that come from incoming debris, such as comet dust and meteorites.
The incoming material is heated up by the atmosphere as it enters, burns up and vaporizes, and even ionizes.
“MAVEN had previously detected the metal ion layer associated with dust from the close passage of Comet Siding Spring last October,” Dr Jakosky said.
Computer simulation of the interaction of the solar wind with ions in the upper atmosphere of Mars: the lines represent the paths of individual ions and the colors represent their energy, and show that the polar plume – red – contains the most-energetic ions. Image credit: X. Fang, University of Colorado / MAVEN Science Team.
The probe has also seen Mars lighting up under the impact of violent solar activity. Because the planet is not protected by a magnetic field like Earth, Coronal Mass Ejection particles directly impact the upper atmosphere, generating aurora.
On Earth, the effect of our magnetic field concentrates auroral displays near the polar regions. Martian aurora is more diffuse, and the effects also could drive the escape of atmospheric gas into space.
MAVEN is also mapping the escaping atmospheric particles.
“We can make maps separated according to low and high solar wind pressure, or other drivers of escape. What we learn about the variability in escape rates will allow us to estimate how the escape rate has changed over Solar System history,” Dr Brain said.
