NASA | GSFC |MAVEN | 2016 Oct 19
[img3="This image shows atomic hydrogen scattering sunlight in the upper atmosphere of Mars, as seen by the Imaging Ultraviolet Spectrograph on NASA’s Mars Atmosphere and Volatile Evolution mission. About 400,000 observations, taken over the course of four days shortly after the spacecraft entered orbit around Mars, were used to create the image. Hydrogen is produced by the breakdown of water, which was once abundant on Mars' surface. Because hydrogen has low atomic mass and is weakly bound by gravity, it extends far from the planet (the darkened circle) and can readily escape. Credits: NASA/Goddard/University of Colorado"]http://www.nasa.gov/sites/default/files ... ct2016.jpg[/img3][hr][/hr]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.
Sophisticated measurements made by a suite of instruments on the Mars Atmosphere and Volatile Evolution, or MAVEN, spacecraft 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. ...
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. Changes in the density of hydrogen in the upper atmosphere were inferred from the flux of hydrogen ions – electrically charged hydrogen atoms – measured by the Solar Wind Ion Analyzer and by the Suprathermal and Thermal Ion Composition instrument. IUVS observed a drop in the amount of sunlight scattered by hydrogen in the upper atmosphere. MAVEN’s magnetometer found a decrease in the occurrence of electromagnetic waves excited by hydrogen ions, indicating a decrease in the amount of hydrogen present. ...
