How did Mars lose so much of its atmosphere? Blame the sun

Mars is home to one of the largest volcanoes in our solar system, Olympus Mons. After circling the Red Planet for more than a full Martian year, NASA’s MAVEN spacecraft has discovered the culprit behind much of Mars’ missing air: a young, rambunctious sun. The findings, published in Friday’s edition of the journal Science, point to solar wind and radiation as one of the main drivers behind atmospheric loss — and may help scientists better understand how a once-habitable planet became such an arid world. “One way to learn about what this early atmosphere could have been like is to understand how it’s been stripped away, and how much has been removed.” Scientists are particularly interested in what happened to the carbon dioxide that used to be in the Martian atmosphere — as a greenhouse gas, it would have helped keep the planet relatively warm. The story makes sense: In the solar system’s early days, the sun was a much more active star, with more intense ultraviolet radiation and stronger solar winds that would more easily strip a planet’s atmosphere if weren’t protected by a strong magnetic field, as Earth is.