The eruption of plumes that reach 260 kilometers above the surface of Mars have puzzled scientists, who so far have no explanation for the unusual activity.

Cloud-like plumes caused by water, carbon dioxide ice, dust storms or auroral light emissions never reach these heights, which rules out any of these conventional explanations. Given that there are currently five orbiters and two rovers working on and around Mars you might be forgiven for thinking that an explanation could be found by one of them, but they were first spotted by a team of amateur astronomers in 2012, writes Christian Schroeder for Quartz.

Mars Sees Massive Clouds Erupt Into Its Atmosphere

Aurora or dust cloud?

An analysis of images collected by the Hubble Space Telescope, as well as amateur astronomers, showed that although massive clouds had previously  been observed on Mars, the 2012 clouds were the biggest yet. A team of scientists led by Agustin Sánchez-Lavega has now published an investigation into the cause of the clouds in the journal Nature.

The scientists have ruled out aurorae as the cause of the clouds, because the aurora would have to be 1,000 times brighter than Earth’s northern lights in order to explain the 2012 observations. Such a strong aurora would require a greater number of charged particles from the Sun, but its activity was not abnormally high at the time.

Another possible explanation is a that the clouds were made up of dust, and caused by an asteroid impact or a volcanic eruption. These two theories were quickly ruled out due to the fact that the behavior of the clouds was inconsistent with the idea that they were made of dust. Observations showed that the clouds disappeared during daytime on Mars, were not observed during the evening, and then reappeared every morning over a period of 10 days.

Sudden temperature drop in Mars’ atmosphere?

The other explanations are water or carbon dioxide ice particles, which do in fact fit the wavelength profile of the reflected light. Water and carbon dioxide molecules are known to occur naturally in the Martian atmosphere at these heights.

However it would take a sudden drop in atmospheric pressure of up to 100 degrees centigrade to make the particles condense into ice. Scientists currently have no viable explanation as to why such a drop would occur, neither has a localized massive drop in temperature been spotted.

Sánchez-Lavega and his team have said that their investigation only partly explains the formation of the mysterious clouds. Mars still holds its fair share of secrets despite the intense efforts of mankind to understand the Red Planet properly.