A large crater on Mars, earlier classified as an impact crater, is actually an ancient exploding super-volcano, a new study has found.
Scientists have determined that a vast circular basin on the face of the Red Planet is actually the remains of an ancient super-volcano eruption.
Researchers note that the basin, recently named Eden Patera, is a volcanic caldera. Because a caldera is a depression, it can look like a crater formed by an impact, rather than a volcano.
"On Mars, young volcanoes have a very distinctive appearance that allows us to identify them," said project leader by Joseph R Michalski, senior scientist at the Planetary Science Institute.
The researchers also suggest a large body of magma loaded with dissolved gas (similar to the carbonation in soda) rose through thin crust to the surface quickly.
Like a bottle of soda that has been shaken, this super-volcano would have blown its contents far and wide if the top came off suddenly.
"This highly explosive type of eruption is a game-changer, spewing many times more ash and other material than typical, younger Martian volcanoes," co-author Jacob E Bleacher of NASA Goddard Space Flight Center said.
"During these types of eruptions on Earth, the debris may spread so far through the atmosphere and remain so long that it alters the global temperature for years," Bleacher said.
After the material is expelled from the eruption, the depression that is left can collapse even further, causing the ground around it to sink.
The assessment is based on images and topographic data from NASA's Mars Odyssey, Mars Global Surveyor and Mars Reconnaissance Orbiter spacecraft, as well as the European Space Agency's Mars Express orbiter.
Volcanoes previously had not been identified in the Arabia Terra region of Mars, where Eden Patera is located. The battered, eroded terrain is known for its impact craters.
Michalski examined this particular basin more closely, he noticed it lacked the typical raised rim of an impact crater. He also could not find a nearby blanket of ejecta, the melted rock that splashes outside the crater when an object hits.
The absence of such key features caused Michalski to suspect volcanic activity. He contacted Bleacher, a volcano specialist, who identified features at Eden Patera that usually indicate volcanism, such as a series of rock ledges that looked like the "bathtub rings" left after a lava lake slowly drains.