The first results from NASA's MAVEN mission may be able to provide clues regarding how Mars lost its atmosphere to space over time.
The observations revealed a new process by which the solar wind can penetrate deep into a planetary atmosphere. They include the first comprehensive measurements of the composition of Mars' upper atmosphere and electrically charged ionosphere.
The results also offer an unprecedented view of ions as they gain the energy that will lead to their escape from the atmosphere.
Bruce Jakosky, MAVEN principal investigator with the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, said that they can see the links in a chain that begins with solar-driven processes acting on gas in the upper atmosphere and leads to atmospheric loss.
Scientists have long thought that measurements of the solar wind could be made only before these particles hit the invisible boundary of the ionosphere. MAVEN's Solar Wind Ion Analyzer, however, has discovered a stream of solar-wind particles that are not deflected but penetrate deep into Mars' upper atmosphere and ionosphere.
Interactions in the upper atmosphere appear to transform this stream of ions into a neutral form that can penetrate to surprisingly low altitudes. Deep in the ionosphere, the stream emerges, almost Houdini-like, in ion form again. The reappearance of these ions, which retain characteristics of the pristine solar wind, provides a new way to track the properties of the solar wind and may make it easier to link drivers of atmospheric loss directly to activity in the upper atmosphere and ionosphere.
NASA's MAVEN mission was observing the upper atmosphere of Mars to help understand climate change on the planet. It entered its science phase on Nov. 16, 2014.
