A new study on the absence of liquid water on the surface of Mars has suggested that an easy escape route of hydrogen from the high altitude upper atmosphere is one of the major reasons.
In the study, researchers at the University of Colorado debunked the earlier assumption of slower loss of water from Mars and argued that the planet lost liquid water at a rapid pace.
Slow Water Loss Debunked
The new theory refutes earlier models that said Martian hydrogen escaped slowly yet steadily.
"Going back to the 1970s, the conventional picture of Martian hydrogen loss has been one of slow, steady escape over long time scales," said Mike Chaffin, lead author of the new study and a research associate at Laboratory for Atmospheric and Space Physics.
According to data from Mars Express, one reason for the rapid hydrogen escape was the floating of water molecules at unusually higher altitudes when the Red planet warms up during summers. This is in contrast to "cold trap" mechanism existing on Earth for keeping atmospheric water closer to the ground.
When the water molecules pile up in the middle atmosphere, ultraviolet rays break them into oxygen and hydrogen. After this, an easy escape by hydrogen follows by defying the Mars' low gravity.
The study has been published in Nature GeoScience.
Though consolidating the findings will require more validations from other data, the finding is significant in underscoring that Mars lost water at a differential rate and no uniform time scale existed.
Chaffin noted that there was high seasonal variation in the matter of water loss from Mars than thought earlier.
Drastic variations in the hydrogen escape were documented by Hubble Telescope of NASA and the Mars Express of ESA way back in 2007. The data said the rate of hydrogen escape became 100 times more than the normal rate when the orbit of Mars came closest to the sun. That makes the old model of slow hydrogen escape from Mars pretty inadequate.
No Cold Trapping
Previous models made a case of water molecules in the Martian atmosphere getting "cold trapped" at lower levels as vapor abundance was low at high altitudes. This was the mechanism with regard to water molecules in Earth's atmosphere.
However, that process does not work with Mars as shown by Mars Express data. What actually happens is, when the lower atmosphere of Red Planet heats up during southern summer, water molecules keep rising higher than normal in the atmosphere and bypass the cold trap to move into middle altitudes.
Ultraviolet light rays split the water molecules to produce atomic oxygen and hydrogen. When hydrogen moves up the higher altitudes thanks to its low weight, the gas escapes the Martian gravity while leaving the heavier oxygen behind.
More details on the hydrogen escape may be gauged by the observations Mars Atmosphere and Volatile Evolution spacecraft that is studying the Martian upper atmosphere and Trace Gas Orbiter of ESA that starts Martian studies in 2018.
The co-authors of the study included LASP planetary scientists Justin Deighan, Nick Schneider, and Ian Stewart.