In March and April of 2012, amateur astronomers with their lenses turned toward Mars saw strange plumes bubble out from the normally round-appearing atmosphere of the Red Planet. The plumes lasted for around 10 days. "Remarkably, the aspect of the features changed rapidly, their shapes going from double-blob protrusions to pillars or finger-plumelike morphologies," says a paper just published in the journal Nature by a team of professional researchers who back up the amateurs' findings. The paper also pretty much says that the researchers have no idea what caused the plumes.
They do have two theories, however.
The first is that the plumes were caused by phenomena similar to our aurora borealis, or Northern Lights, the process by which electrically charged particles from the sun are funneled to the poles of our planet, where they collide with gas molecules and produce eerie glowing lights.
"Mars aurorae have been observed near where the plume occurs, a region with a large anomaly in the crustal magnetic field that can drive the precipitation of solar wind particles into the atmosphere," says the research paper.
However, the document goes on to argue against this theory as it would have "required exceptional influx of energetic particles over days," from the sun, and stating that the solar activity in 2012 just wasn't strong enough to release such a stream of aurora-producing particles.
The second idea is that the plumes were actually high-flying clouds.
"One idea we've discussed is that the features are caused by a reflective cloud of water-ice, carbon dioxide-ice or dust particles, but this would require exceptional deviations from standard atmospheric circulation models to explain cloud formations at such high altitudes," says Agustin Sánchez-Lavega in a European Space Agency release about the phenomena. Sánchez-Lavega is from the Universidad del País Vasco in Spain, and is lead author of the Nature paper.
But there are problems with this theory as well. Although clouds have certainly been seen on Mars, they typically don't go higher than 60 miles, or about 100km, above the planet's surface, according to National Geographic. These clouds were seen twice that high, however, bumping out from the "Martian limb," or the observed edge of the planet. For water to have condensed at such an altitude, the researchers said in the paper, would have required "anomalously cold thermospheric temperatures" with a temperature drop of more than 50 Kelvin (about 370 degrees Fahrenheit) below the normal temperature at that level of the atmosphere. For carbon dioxide to have done the same, the temperature drop would have to have been more than double that.
As for the dust hypothesis, the researchers say it would have required "vigorous vertical transport" up to at least 180km (about 111 miles) above the surface. Such an upward wind might be created by convection -- the Martian surface would absorb the sun's heat during the day, and the heat would rise and create wind currents. Therefore, the researchers say that such winds would likely happen only at noon, and the fact that the plumes were seen in the Martian morning along what's known as the terminator (the line between night and day) makes the dust hypothesis "difficult to support."
So what exactly is going on in the Martian atmosphere?
Aside from these two theories, scientists don't really know. But thanks to the work of citizen astronomers backed up with data from the Hubble telescope (which, researchers just realized, spotted a similar event in 1997) they now know the phenomenon exists and can put more time and energy into understanding it.
"We just have to keep watching [the planet's edge] with telescopes on Earth and with spacecraft," Sánchez-Lavega told National Geographic. "And because they're so numerous, so widely spread around Earth and so dedicated, amateurs will continue to play a fundamental role."
Another source of help will also be on the way in 2016. That's when the ESA will be launching its ExoMars Trace Gas Orbiter, which will circle the Red Planet to learn more about the methane and other trace gases in the Martian atmosphere.