Back in 2012, our crimson-hued celestial neighbor showcased two enormous cloud-like protrusions, both persisting in the Martian upper atmosphere for over a week. They were originally spotted by amateur astronomers, who noted that one of the plumes managed to reach an astonishing height of 250 kilometers (155 miles) above the surface.
Although many causes have been suggested, their true origin has remained decidedly mysterious. Now, a new study published in the Journal of Geophysical Research: Space Physics has pinned the blame on a seemingly unlikely source: the Sun.
The team of researchers, belonging to the European Space Agency’s (ESA) Mars Express mission, realized that the plumes reached the height of the ionosphere, the section of the atmosphere that directly interacts with the incoming solar wind of highly energetic particles.
They subsequently found evidence hidden within the databanks of Mars Express that a spectacularly powerful release of matter and electromagnetic energy from the Sun – something known as a coronal mass ejection (CME) – impacted the Martian atmosphere at the time the plumes appeared.
“One idea is that a fast-travelling CME causes a significant perturbation in the ionosphere,” David Andrews, a researcher at the Swedish Institute of Space Physics, and lead author of the paper, said in a statement. This would have resulted “in dust and ice grains residing at high altitudes in the upper atmosphere being pushed around by the ionospheric plasma and magnetic fields, and then lofted to even higher altitudes by electrical charging.”
Volcanic activity hasn’t been around on Mars for perhaps many millions of years, and no sizeable meteor impacts were observed around the time of the 2012 plume events. The winds on Mars are not really strong enough to lift significant volumes of dust up into space, and the plumes appeared far higher than where typical clouds of frozen carbon dioxide and water are able to form.
Although the spacecraft orbiting Mars were not able to capture the evolution of the plumes at the time, scientists have been pouring over the data collected by Mars Express ever since. Instrumentation aboard this particular bucket of bolts is able to detect changes in the regional solar wind, and measurements were being taken at the time the plumes formed.
It was clear that a large CME was detected at the time, one that would have certainly impacted the upper atmosphere of Mars. Such a powerful source of energy would have markedly and suddenly increased the generation, and escape, of electrically charged particles from the ionosphere, creating a strong upwelling effect for any dust and ice particles nearby.
Although the team were not able to see any signatures in the ionosphere that conclusively, definitively link it to the emergence of the southern hemisphere-based plumes, this mechanism is certainly the most likely explanation to date.
A coronal mass ejection often accompanies a solar flare, pictured, as captured by the Solar Dynamics Observatory in 2012. NASA Goddard Space Flight Center
These plume events are rare, though, so the evidence remains strongly circumstantial. In 1997, a significant CME struck Earth, and a plume on Mars was seen at the same time, but scientists were unable to assess how much the CME actually interacted with Mars. In addition, CMEs have impacted Mars with no accompanying plume observed.
Either way, this team of researchers aren’t taking any chances this time around. “We are now going to use the webcam on Mars Express for more frequent coverage of the planet,” Dmitri Titov, a Mars Express project scientist, noted in the statement.
Image in text: A bizarre plume-like feature emerging from Mars on March 20, 2012 captured by an amateur astronomer’s telescope. In this image, the Martian north pole is towards the bottom, and the south pole to the top. W. Jaeschke