Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has observed two unexpected phenomena in the Martian atmosphere: an unexplained high-altitude dust cloud and aurora that reaches deep into the Martian atmosphere.
The presence of the dust at orbital altitudes from about 150 - 300 km (93 - 190 miles) above the surface was not predicted. Although the source and composition of the dust are unknown, there is no hazard to MAVEN and other spacecraft orbiting Mars, NASA said.
Laila Andersson of the University of Colorado's Laboratory for Atmospherics and Space Physics (CU LASP) in Boulder, Colorado said that if the dust originates from the atmosphere, this suggests we are missing some fundamental process in the Martian atmosphere.
The cloud was detected by the spacecraft’s Langmuir Probe and Waves (LPW) instrument, and has been present the whole time MAVEN has been in operation. It is unknown if the cloud is a temporary phenomenon or something long lasting. The cloud density is greatest at lower altitudes. However, even in the densest areas it is still very thin. So far, no indication of its presence has been seen in observations from any of the other MAVEN instruments.
Possible sources for the observed dust include dust wafted up from the atmosphere; dust coming from Phobos and Deimos, the two moons of Mars; dust moving in the solar wind away from the Sun; or debris orbiting the Sun from comets. However, no known process on Mars can explain the appearance of dust in the observed locations from any of these sources.
MAVEN's Imaging Ultraviolet Spectrograph (IUVS) observed what scientists have named "Christmas lights." For five days just before December 25, MAVEN saw a bright ultraviolet auroral glow spanning Mars' northern hemisphere. Aurora, known on Earth as northern or southern lights, are caused by energetic particles like electrons crashing down into the atmosphere and causing the gas to glow.
A map of IUVS’s auroral detections in December 2014 overlaid on Mars’ surface. The map shows that the aurora was widespread in the northern hemisphere, not tied to any geographic location. The aurora was detected in all observations during a 5-day period. Image credit: University of Colorado.
"What's especially surprising about the aurora we saw is how deep in the atmosphere it occurs - much deeper than at Earth or elsewhere on Mars,” said Arnaud Stiepen, IUVS team member at the University of Colorado. “The electrons producing it must be really energetic."
The source of the energetic particles appears to be the Sun. MAVEN's Solar Energetic Particle instrument detected a huge surge in energetic electrons at the onset of the aurora. Billions of years ago, Mars lost a global protective magnetic field like Earth has, so solar particles can directly strike the atmosphere. The electrons producing the aurora have about 100 times more energy than you get from a spark of house current, so they can penetrate deeply in the atmosphere.
Featured image: Artist’s conception of MAVEN’s Imaging UltraViolet Spectrograph (IUVS) observing the “Christmas Lights Aurora" on Mars. MAVEN observations show that aurora on Mars is similar to Earth’s "Northern Lights" but has a different origin. Image credit: University of Colorado.