Powerful solar winds stripped away the atmosphere of Mars billions of years ago, leaving it a dry and barren world. Prior studies found crucial evidence of liquid water that used to flow on the surface of the Red Planet, particularly dried up lake systems.

However, scientists have been arguing about what exactly caused the disappearance of Martian atmosphere. Past theories include chemical reactions expelled by rock formations that trapped gases underground while others say it was solar radiation that bombarded this already tenuous atmosphere over time.

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In this new study, a NASA team of scientists was able to measure the argon gas content of the atmosphere of Mars and discovered how this gas is the primary driving force for the disappearance of Martian atmosphere.

According to NASA's MAVEN (Mars Atmosphere and Volatile Evolution Mission) principal investigator, Bruce Jakosky from the University of Colorado, Boulder, we have determined that most of the gas that was ever present in the Mars atmosphere was already lost to space. More specifically, we have measured that 65 percent of argon that used to be present in the atmosphere escaped into deep space.

In addition, data used for this study was based on the Sample Analysis at Mars instrument onboard NASA's Curiosity rover, including mass spectrometry measurements that analyzed the argon composition from atmospheric remnants. Since argon cannot produce a chemical reaction with Martian rocks and soil, this leaves a process that involves "sputtering" where solar wind gradually strips away the atmosphere.

The team was able to measure two argon isotopes where one is heavier than the other. The lighter argon isotope was easily carried away by solar winds. Assuming that there is an equal ratio of the two argon isotopes, scientists were able to measure how much was blown away by solar winds.

According to Paul Mahaffy of NASA's Goddard Space Flight Center, these combined measurements provided a better analysis of how much argon has been lost from Mars to space in the span of billions of years. The team was then able to calculate how the other gases disappeared during the same period of time with this process.

Jakosky says that the majority of carbon dioxide in Martian atmosphere was also lost to space with the same process of sputtering. There are other processes that may have caused this carbon loss which also gives an estimate of the minimum carbon amount that disappeared into space.

This new study is published in the journal Science.