When the sun huffs and puffs, its solar wind blows part of Mars' atmosphere out to space. That's the key finding announced at a NASA press conference on Thursday by researchers working on the Mars Atmosphere and Volatile Evolution (MAVEN) mission.
The MAVEN mission's spacecraft has been circling the Red Planet for over a year now to study its atmosphere and determine how so much of it was lost over its history, transforming it from a once wet and warm Earth-like planet to the cold, dry place of so many sci-fi storylines.
Figuring out what happened to the Martian atmosphere is a big deal because it helps scientists understand why some planets can or can't host life while others like Mars go from potential beach destination to inhospitable.
The culprit in the loss of Mars' atmosphere is the solar wind, a stream of mostly protons and electrons flowing from our star's atmosphere at a speed of about a million miles per hour. The solar wind also carries a magnetic field that can generate an electric field as it flows past Mars. This electric field is then capable of accelerating electrically charged gas ions in the planet's upper atmosphere and shooting them out into space, similar to the way a baseball might be launched out of the field of play when a batter hits a high foul ball or home run.
MAVEN has eight sensors that gather data on Mars' upper atmosphere and its interaction with the sun and solar wind. According to MAVEN measurements, the solar wind strips away gas in the Martian atmosphere at a rate of about 100 grams (roughly a quarter pound) every second.
"Like the theft of a few coins from a cash register every day, the loss becomes significant over time," said Bruce Jakosky, MAVEN principal investigator at the University of Colorado-Boulder. "We've seen that the atmospheric erosion increases significantly during solar storms, so we think the loss rate was much higher billions of years ago when the sun was young and more active."
Jakosky added that geology on Mars seems to show that water was abundant on the planet until about 3.7 billion years ago, leading the researchers to hypothesize that more active solar storms stripped away most of the atmosphere during a period sometime between 3.7 billion and 4.2 billion years ago.
The fact that the sun is less active and prone to big solar wind storms today is just one reason Jakosky says we shouldn't worry too much about something similar happening to Earth's atmosphere anytime soon. The other factor that protects our planet from turning into a dead, frozen hellscape is Earth's rocking magnetic field that shields us from the brunt of the solar wind's wrath. Mars has no such magnetic field to protect its upper atmosphere from the ion-stripping effects of the solar wind.
"Understanding what happened to the Mars atmosphere will inform our knowledge of the dynamics and evolution of any planetary atmosphere," NASA's John Grunsfeld said in a news release. "Learning what can cause changes to a planet's environment from one that could host microbes at the surface to one that doesn't is important to know, and is a key question that is being addressed in NASA's journey to Mars."
Speaking of that trip to Mars, though, Jakosky added that dreams of someday releasing carbon dioxide sequestered in Mars to aid global warming and make the planet more like Earth will prove more difficult in light of the new findings. That's because Mars' carbon dioxide is "gone, it's blown away," he said.
Maybe that's a good thing. Someone call Elon Musk and tell him to put away those nukes he wanted to use to kickstart the process.