NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission only entered its science phase in mid-November after slipping into orbit two months earlier, but it is already proving to be worth every penny, having beamed back some exciting data. Back in December, the orbiter began to reveal key features of a chain of solar-driven processes that led to the loss of the planet’s atmosphere over time, which is one of the mission’s primary objectives. Now, the craft has observed two rather unexpected phenomena: a bizarre high-altitude dust cloud that scientists are struggling to explain, and an aurora that extends deep into the atmosphere.
Auroras, known colloquially as Northern or Southern lights on Earth, are natural events caused by energetic charged particles, such as electrons and protons, slamming into the atmosphere from above, causing excitation of gases in the atmosphere that subsequently makes them glow. We regularly see these in the skies above our own planet, but this phenomenon was also observed in the Martian atmosphere late last year by MAVEN’s Imaging Ultraviolet Spectrograph (IUVS).
According to a NASA statement, for five days on the run up to Christmas last year, the probe picked up a bright UV auroral glow sprawled across the planet’s northern hemisphere, not tied to any particular spot. As pointed out by the BBC, although Martian auroras have been detected previously by Europe’s Mars Express spacecraft, this event caused a stir amongst scientists because it reached surprising depths in Mars’ atmosphere—significantly deeper than those seen on our planet or anywhere else on Mars.
“The electrons producing it must be really energetic,” Arnaud Stiepen, IUVS scientist at the University of Colorado, said in a news release.
Although scientists were surprised at the depths of the UV aurora, it makes sense that this could occur due to the fact that Mars lost its protective magnetic field billions of years ago, whereas Earth is still shielded by one. This means that energetic particles, which probably came from the sun, are able to directly smash into the Martian atmosphere and penetrate deeply.
Interestingly, MAVEN also detected a second surprise: the presence of an unpredicted high-altitude dust cloud, which is lingering between 93 miles (150 km) and 190 miles (300 km) above the Martian surface. Although it has been present the whole time MAVEN has been collecting data, scientists are still unsure as to whether it is a temporary phenomenon or a long-standing feature.
“If the dust originates from the atmosphere,” explains Laila Andersson of the University of Colorado, “this suggests we are missing some fundamental process in the Martian atmosphere.”
Scientists aren’t quite sure of the origins of the dust, but they have put forward a few hypotheses, such as dust wafting up from the atmosphere, debris from comets or dust leaking from Mars’ two moons, Phobos and Deimos. While these may represent valid sources, none of the processes currently understood on Mars can explain why the dust would appear in the observed areas.