After investigating the upper atmosphere of the Red Planet for a full Martian year, NASA’s MAVEN mission has determined that the escaping water does not always go gently into space.
A suite of instruments on the Mars Atmosphere and Volatile Evolution (MAVEN) made sophisticated measurements, and the finding revealed the ups and downs of hydrogen escape, and therefore water loss.
The escape rate peaked when Mars was at its closest point to the sun and dropped off when the planet was farthest from the sun.
The rate of loss varied dramatically overall, with 10 times more hydrogen escaping at the maximum.
The MAVEN data are crucial for figuring out the total amount of water lost over billions of years, suggested researchers from the University of California at Berkeley.
These scientists analyzed data from two of the spacecraft’s instruments.
Hydrogen in Mars’ upper atmosphere comes from water vapor in the lower atmosphere.
An atmospheric water molecule can be broken apart by sunlight, releasing the two hydrogen atoms from the oxygen atom that they had been bound to.
Several processes at work in Mars’ upper atmosphere may then act on the hydrogen, leading to its escape.
This loss had long been assumed to be more-or-less constant, like a slow leak in a tire. But previous observations made using NASA’s Hubble Space Telescope and ESA’s Mars Express orbiter found unexpected fluctuations.
Only a handful of these measurements have been made so far, and most were essentially snapshots, taken months or years apart.
MAVEN has been tracking the hydrogen escape without interruption over the course of a Martian year, which lasts nearly two Earth years.
In the most detailed observations of hydrogen loss to date, four of MAVEN’s instruments detected the factor-of-10 change in the rate of escape.
By investigating hydrogen escape in multiple ways, the MAVEN team will be able to work out which factors drive the escape.
Scientists already know that Mars’ elliptical orbit causes the intensity of the sunlight reaching Mars to vary by 40% during a Martian year.
There also is a seasonal effect that controls how much water vapor is present in the lower atmosphere, as well as variations in how much water makes it into the upper atmosphere. The 11-year cycle of the sun’s activity is another likely factor.
By making observations for a second Mars year and during different parts of the solar cycle, the scientists will be better able to distinguish among these effects.
MAVEN is continuing these observations in its extended mission, which has been approved until at least September 2018.
News Source: NASA.
Figure legend: This Knowridge.com image is credited to NASA/Goddard/University of Colorado.