That process, known as sputtering, blew most of the argon and other atmospheric gases into space, the MAVEN team concluded.
Mars' lack of liquid water might be a result of solar wind and radiation that stripped it of its atmospheric gas - and the ability to support life - leaving behind a frigid desert world. The mission's objectives include finding out how the planet's water and atmosphere, believed to have once been considerable, were lost over time.
"The whole goal is to really understand all of the (atmospheric) loss processes, and how the sun influences loss, and using that to infer what the atmosphere was like billions of years ago", Slipski said. In other cases, such as on Mars, solar wind and radiation are responsible for the bulk of the lost gases. A paper detailing the team's latest findings was published in Science today, and the research shows that a whopping 65 percent of the argon that was ever in Mars's atmosphere has been blown out into space. It's possible microbial life cold have existed at the surface early in Mars' history. Still, previous research has unearthed ample evidence that Mars was once covered in water, with features resembling dry riverbeds and minerals that could have formed only in the presence of water.
"This discovery is a significant step toward unraveling the mystery of Mars' past environments", said Elsayed Talaat, MAVEN Program Scientist, at NASA Headquarters in Washington.
The planet loses about 1.3 kilograms per second of 'important oxygen'. The lighter variant of argon is more likely to be blown into space, and by studying the ratio of lighter and heavier argon, the MAVEN team could calculate the likely effects of the solar wind.
"In this process, ions which have been created in the Mars upper atmosphere, and extended corona of gas surrounding the planet, are grabbed or "picked-up" by the solar wind and accelerated to high velocities", Professor Jakosky said.
MAVEN was launched aboard an Atlas V launch vehicle on November 18th, 2013.
NASA's Mars Reconnaissance Orbiter (MRO) continues to deliver the most sharp-eyed coverage ever achieved by a camera at Mars as it completes its 50,000th orbit.
The data was collected by the Mars Atmosphere and Volatile Evolution, or MAVEN, spacecraft, one of eight satellites and rovers now operating around or on Mars.
The reason, per the study, was strong solar wind and radiation. All knowledge will culminate in the Journey to Mars mission, which will see a group of astronauts travel to the Red Planet to test if life can survive there.
It had previously been shown atmospheric gas had been lost to space, but NASA's new measurements from its MAVEN spacecraft show just how much. Isotopes are atoms of the same element but with various masses due to different neutron numbers in the nucleus.
The scientists found that the planet is rich in one argon isotope, Ar, but depleted of the lightest, Ar.
As a "noble gas", argon cannot react chemically with anything; the only process that can remove it to space is a physical process called "sputtering" by the solar wind.
Once they determined the amount of argon lost by sputtering, they could use this information to determine the sputtering loss of other atoms and molecules, including carbon dioxide.
Carbon dioxide is of interest to the researchers because it is the most plentiful gas in the Martian atmosphere and because it is a greenhouse gas that can retain heat and warm the planet.
The base of Mars' Mount Sharp is pictured in this NASA handout photo taken by the Curiosity rover. "Since temperatures at the surface have been so strongly affected by loss to space, these processes may also have determined the history of the habitability of Mars by microbes".
"Using measurements from both platforms points to the value of having multiple missions that make complementary measurements", said Mahaffy.