A vast circular basin on the surface of Mars, previously classified as an impact crater, may actually be the remains of an ancient supervolcano eruption, researchers at NASA and the Planetary Science Institute in Tucson suggest.
Scientist said assessment of a volcanic origin for the feature known as the Eden Patera basin 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.
Eden Patera is a volcanic caldera, they said; because a caldera is a depression, it can look like a crater formed by an impact.
"On Mars, young volcanoes have a very distinctive appearance that allows us to identify them," Joseph Michalski of the Tucson institute said. "The long-standing question has been what ancient volcanoes on Mars look like. Perhaps they look like this one."
If sufficient material is ejected in a supervolcano eruption, the scientists said, the ground surrounding the volcano can collapse and sink.
Supervolcano eruptions in the past on Earth created areas like Yellowstone National Park in the western United States, Lake Toba in Indonesia and Lake Taupo in New Zealand, they said.
Observations of features at Eden Patera suggested volcanism rather than an impact, researchers noted, including a series of rock ledges that looked like the "bathtub rings" left after a lava lake slowly drains, and faults and valleys that occur when the ground collapses because of activity below the surface.