Solar wind turned Mars into dry, cold planet: Study

Cape Canaveral, Florida : About 4 billion years ago when life was starting on Earth, Mars like Earth also had a dense atmosphere, which kept the planet wet and warm, according to the study in this week's issue of the journal Science.

But, the measurements now shows that Mars has lost 66 percent of its argon.

Over time, energized particles in the solar wind stripped off Mars' atmosphere, leaving a thin and still-shrinking envelope of gases around the planet, measurements by one of NASA's Mars-orbiting spacecraft show.

"The lines of evidence that point to the period between about 3.7 billion years ago and 4 billion years ago as when Mars went bad," lead researcher Bruce Jakosky with the University of Colorado in Boulder, said over phone.

Conditions on early Mars could have supported microbes, but as the thick atmosphere around the planet disappeared, "it went from a wet planet that could support life at the surface to the cold, dry planet we see today." Jakosky said.

The findings offer insight into why a planet that started off similar to Earth ended up so different and what conditions could make planets beyond the solar system suitable for life. The data was collected by the Mars Atmosphere and Volatile Evolution, or MAVEN, spacecraft, one of eight satellites and rovers currently operating around or on Mars.

"It is the answer we expected in some ways," Jakosky said. "It meshes well with everything else that's going on Mars."

"The lines of evidence point to the period between about 3.7 billion years ago and 4 billion years ago as when Mars went bad," lead researcher Bruce Jakosky with the 

Scientists are not sure why Mars' atmosphere became vulnerable to the solar wind, but suspect it had to do with the loss of the planet's magnetic field.

Earth, by contrast, has a liquid metal core that generates a protective magnetic shield that deflects the solar wind.

Mars' atmosphere was and is dominated by carbon dioxide.