A mysterious blob-like plume has risen from Mars' surface again and again, and researchers are still struggling to understand what exactly it could be. (Photo : JPL/NASA/STScI)

For many astronomers, amateur and expert alike, Mars is like that vacation destination you've been dreaming about for years. They can tell you all the greatest spots for sightseeing, and impressive details about the Red Planet's stunning landmarks, even when they have never actually been there. My own father used to love showing off his massive globe of Mars - which took up the great majority of our tiny coffee table - to less-than-enthusiastic guests.

However, for all that we know about the planet, Mars loves to occasionally remind us that it still has plenty of mysteries to serve up. Such was the case on March 12, 2012, when amateur astronomers around the world noticed a strange blob rising out of the planet's southern hemisphere, soaring to 250 kilometers (155 miles) above the surface.

Much like the moon Titan's mysterious magic island, astronomers had absolutely no idea what this blob was. All they knew was that it resembled a set of plumes - perhaps of material erupting from the Red Planet.

According to the European Space Agency (ESA), who, with NASA, observed the plumes in action, "the features developed in less than 10 hours, covering an area of up to 1000 x 500 km, and remained visible for around 10 days, changing their structure from day to day."

In an incredibly bad stroke of luck, neither of the space agencies had orbital telescopes watching Mars when the blob appeared. Even their own Mars orbiters happened to be on the other side of the planet, missing the event for the entire 10 days.

That left only Earth-side telescope observations for astronomers to work with. Later in April, a similar plume appeared, giving Agustin Sanchez-Lavega of the Universidad del País Vasco in Spain more material from which to determine what they were. Admittedly, he too was first scratching his head in confusion.

"At about 250 km, the division between the atmosphere [of Mars] and outer space is very thin, so the reported plumes are extremely unexpected," he explained in a statement. (Scroll to read on...)



However, after checking archived Hubble Space Telescope images taken between 1995 and 1999, and databases of amateur images spanning from 2001 to 2014, Sanchez-Lavega and his colleagues determined that smaller plumes (reaching to only about 100 km) actually happen quite frequently. In May 1997, Hubble even managed to capture a plume that reached heights similar to the 2012 pair.

Knowing that this event wasn't a freak occurrence, the team began to consider natural phenomena that repeats even on dead worlds, and could send enough material into an atmosphere that it could be seen from space. The results are detailed in the journal Nature.

Volcanoes, of course, were the first consideration. A massive summit pumping material into the atmosphere would fit the bill perfectly.

However, Nicholas Heavens of Hampton University in Virginia, who was not involved in the study, recently explained to New Scientist how that theory would quickly be ruled out.

"You would think that something large enough to dump that much vapor in the atmosphere would be picked up," he said, adding that no orbiter or rover has ever picked up readings that would indicate the Red Planet's volcanoes are still active.

That led Sanchez-Lavega and his team to think harder.

"One idea we've discussed is that the features are caused by a reflective cloud of water-ice, carbon dioxide-ice or dust particles," he said, "but this would require exceptional deviations from standard atmospheric circulation models to explain cloud formations at such high altitudes."

"Another idea is that they are related to an aurora emission," ESA researcher Antonio Garcia Munoz added.

And indeed, auroras have previously been observed occurring where the plumes were last spotted.

Still, at the end of the day, the origin of these Martian plumes is still one of our solar system's freshest and greatest mysteries, and likely will hold the attention of experts and amateurs alike for years to come.

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