The dust is about 150 kilometres to 300 kilometres above the surface. NASA said it was not predicted and its the source and composition are unknown.
“If the dust originates from the atmosphere, this suggests we are missing some fundamental process in the Martian atmosphere,” said Laila Andersson of the University of Colorado’s Laboratory for Atmospherics and Space Physics (CU LASP), Boulder, Colorado.
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.
Scientists speculate the dust could have wafted up from the atmosphere, come from Phobos and Deimos, the two moons of Mars, be moving in the solar wind away from the sun or from debris from comets.
Meanwhile, MAVEN’s Imaging Ultraviolet Spectrograph (IUVS) has also observed 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.
“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 around 25 December last year. It was dubbed the “Christmas Lights” by scientists.
Billions of years ago, Mars lost a global protective magnetic field like Earth has, so solar particles can directly strike the atmosphere.
The findings were presented at the 46th Lunar and Planetary Science Conference in The Woodlands, Texas.
MAVEN was launched to Mars to help solve the mystery of how the Red Planet lost most of its atmosphere and much of its water. The spacecraft arrived at Mars on 21 September last year and is four months into its Earth-year-long primary mission.