(CN) – 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.
In findings published Friday in the journal Science, researchers show that a bright, young sun was responsible for the Red Planet’s dramatic transformation.
“We’ve determined that most of the gas ever present in the Mars atmosphere has been lost to space,” said Bruce Jakosky, lead author and professor at the University of Colorado, Boulder.
The discovery is based on data collected by NASA’s Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft, which launched in 2013.
“The team made this determination from the latest result, which reveals that about 65 percent of the argon that was ever in the atmosphere has been lost to space.”
MAVEN researchers had previously announced measurements showing that gas from the Martian atmosphere was being lost to space, which also allowed the crew to describe how it was being stripped away. The new analysis uses measurements of the planet’s current atmospheric makeup to establish the first estimate of how much gas has been removed over time.
Liquid water – an essential resource for known life – is not stable on the Red Planet’s surface today because the atmosphere is too thin and cold to support it. However, certain features on the planet suggest the ancient Martian climate was quite different and likely warm enough for water to flow on the surface for extended periods.
While several scenarios can cause a planet to lose some of its atmosphere, including chemical reactions that lock gas away in surface rocks, the new findings show that solar wind and radiation were the culprits behind the planet’s atmospheric loss and subsequent transformation of Mars’ climate. Any life would have been driven underground or forced into a rare surface oasis.
Jakosky’s team determined this after measuring the atmospheric abundance of two different isotopes – atoms of the same element with different masses – of argon gas. Since the lighter of the two isotopes gets pulled into space more readily, it leaves the gas remaining behind enriched in the heavier isotope. The researchers measured this enrichment and its variations at different altitudes in the atmosphere to estimate what percentage of the atmospheric gas was lost to space.
The team tracked argon since it can be removed only by sputtering, a process in which ions picked up by solar wind impact Mars at high speeds, physically knocking atmospheric gas into space. Once they determined how much argon was lost due to sputtering, the researchers were able to use the efficiency of sputtering to measure the loss of other atoms and molecules, such as carbon dioxide.
Researchers measure carbon dioxide because it is the primary molecule within the Red Planet’s atmosphere and because it can retain heat and warm the planet.
“We determined that the majority of the planet’s carbon dioxide also has been lost to space by sputtering,” Jakosky said. “There are other processes that can remove carbon dioxide, so this gives the minimum amount of carbon dioxide that’s been lost to space.”