Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. (credit: NASA/GSFC)
Since Mariner 4 flew by Mars more than five decades ago, scientists have understood the red planet to be a cold, dry world. Now they know why. After looking at the first six months of data collected by NASA’s MAVEN spacecraft, sent to Mars to monitor its upper atmosphere, scientists say the solar wind has stripped away most of the atmosphere’s carbon dioxide and oxygen.
Although the planet’s atmosphere is presently losing about 100 grams per second— the equivalent of a McDonald’s Quarter Pounder—scientists say Mars lost the bulk of its once thick atmosphere billions of years ago, a relatively short time after our solar system formed. The findings were published in multiple articles Thursday in Science and Geophysical Research Letters.
Mars once had a strong magnetic field—like Earth does now—produced by a dynamo effect from its interior heat. But as the smaller planet cooled, Mars lost its magnetic field some time around 4.2 billion years ago, scientists say. During the next several hundred million years, the Sun’s powerful solar wind stripped particles away from the unprotected Martian atmosphere at a rate 100 to 1,000 times greater than today.