GREENBELT, Md., Oct. 2 (UPI) -- Some of Mars' deep craters were actually ancient supervolcanoes that may have changed the planet's climate, U.S. and British researchers suggest.
Jacob Bleacher of NASA's Goddard Space Flight Center and colleague Joseph Michalski of the Planetary Science Institute and London's Natural History Museum say several irregularly shaped craters in Mars' Arabia Terra region have a structure similar to supervolcanoes on Earth.
One of them, Eden Patera, is more than a mile deep and around 43 miles wide.
Such geological features suggest the existence of ancient supervolcanoes that could have spewed ash over wide areas Mars and perhaps affected its early climate, they said, although they acknowledge not all geologists agree with them.
"Yes, there is some resistance to the idea," Michalski told NBC News in an email. "That is perfectly natural for a totally new idea."
Billions of years ago, Martian supervolcanoes could have discharged hundreds of cubic miles' worth of magma until the surface around the volcanoes collapsed, leaving deep, irregular craters behind, Michalski and Bleacher suggested.
While other geologists consider meteor impacts the more likely source of the craters, Michalski and Bleacher maintain their features don't fit the criteria for impact craters.
They don't have well-defined rims or evidence of impact debris, the two say, and are too deep to fit the profile for eroded ancient impact craters.
In a paper published in the journal Nature, Michalski and Bleacher say they've identified five possible supervolcanoes and suggest more might be found elsewhere on Mars.