Scientists have found evidence of massive, extremely explosive ancient volcanoes on Mars that could once have had a big influence on the climate of the Red Planet.
The discovery of such "supervolcanoes" on Mars "fundamentally changes the picture of ancient volcanism and climate evolution on Mars," said a paper published Wednesday in the journal Nature, describing the evidence.
Supervolcanoes are giant, very explosive volcanoes that blast out more than 1,000 cubic kilometres of volcanic material when they erupt – enough to fill two lakes the size of Lake Erie. On Earth, one of the most well-known is the one beneath Yellowstone National Park in the U.S. Because supervolcanoes erupt too quickly and violently to build up a large amount of lava around their vent, they don't have the characteristic cone shape typically associated with smaller volcanoes.
The ancient supervolcanoes on Mars, which are estimated to have been active more than 3.5 billion years ago, now appear as irregularly shaped craters on a highland area of Mars called Arabia Terra. Previously, scientists that thought the craters might have been caused by the impact of an object such as a meteor.
The crater Oxus Patera may also have been a supervolcano. Irregular basins within the crater represent multiple stages of collapse. Mountains within the 30-km-diameter crater are composed of powdery materials that may represent volcanic ash deposits. (ESA/Mars Express/Freie Universitat Berlin/Google)
However, Joseph Michalski, a researcher at the Planetary Science institute in Tucson, Ariz., and Jacob Bleacher, a researcher at the NASA Goddard Space Flight Center at the Natural History Museum in London, England, carefully analyzed the craters, including one known as Eden patera that was described as the "best example."
They found that Eden patera did not show any evidence of an impact – for example, it isn't surrounded by debris that would have been ejected by an impact, it doesn't have an uplifted rim, it isn't circular enough, and it's much deeper than would be expected for an impact crater of its diameter.
Meanwhile, it had features very similar to those of supervolcanoes on Earth. The researchers concluded it is more likely the craters were produced by supervolcanoes that underwent a massive eruption, and then collapsed.
The apparent supervolcanoes were also well positioned to have produced huge deposits of layered rock and powdery sediments in the areas where Curiosity and previous rovers landed. Up until now, scientists have puzzled over where those deposits might have come from.
Researchers had already known about younger volcanoes on Mars, smaller than supervolcanoes (although some, such as Olympus Mons, are very large nevertheless), which are similar in shape to those in Hawaii, said Michalski in a statement from the Museum of Natural History.
"We have always wondered where the ancient volcanoes are," he added. "It is possible that the most ancient volcanoes were much more explosive and formed structures similar to what we now see in Arabia Terra."
The researchers suggest in their paper that other craters on highland areas of Mars should be "reconsidered" as possibly forming from supervolcanoes.
Ancient supervolcanoes may have significantly altered the environment on Mars, the researchers said. For example, sulphur from the volcanoes could have generated compounds such as those that cause acid rain on Earth and "strongly perturbed the Martian climate, sending it into periods of significant warming or substantial cooling," they wrote.
"If future work shows that supervolcanoes were present more widely on ancient Mars," Michalski said, "it would completely change estimates of how the atmosphere formed from volcanic gases, how sediments formed from volcanic ash and how habitable the surface might have been."
