Mars is regarded as the most Earth-like of the planets in the Solar System, but its atmosphere is only 0.6 percent as dense as Earth's and is constantly leaking what little air it has into space. NASA'S Mars Atmosphere and Volatile Evolution (MAVEN) Mars orbiter is providing new insights into the loss of the Martian atmosphere by discovering how the solar winds penetrate to surprisingly low altitudes.
Blessed with its powerful magnetic field, the Earth's atmosphere is protected from the constant blast of light, radiation, and subatomic particles emitted from the Sun. Mars however, is not so fortunate. What little magnetic field it has is extremely weak and patchy, and as the solar winds strike the upper reaches of the atmosphere, they strip it away atom by atom. How this process works is one of the key mysteries for scientists studying the planet.
NASA says that the MAVEN spacecraft, which is tasked with making a detailed study of the Martian atmosphere, has discovered a new process that demonstrates just how deep the impact of the solar wind is on the air around Mars. The unmanned orbiter's Suprathermal and Thermal Ion Composition (STATIC) instrument found a plume of ionized gas rising from the poles of Mars into the tenuous layer of ions and electrons, called the ionosphere, that ranges from 75 to 300 mi (120 to 480 km) above the surface, and was able to measure its temperature. As it orbits, MAVEN's lowest altitude dips into the ionosphere, allowing it to directly measure its temperature and composition.
Meanwhile, another of MAVEN's instruments, the Neutral Gas and Ion Mass Spectrometer, studies how the lower atmosphere and the upper atmosphere interact, and the Solar Wind Ion Analyzer measures incoming high-energy solar particles.
According to the space agency, the latter instrument returned surprising results. It had been previously believed that the ionosphere acted as a barrier to the solar winds and that most of the atmospheric loss would occur there, but MAVEN discovered that a stream of solar particles was penetrating deep into the lower layers of the atmosphere.
NASA says that this is due to the ionized solar particles somehow acquiring a neutral charge as they hit the ionosphere. Since they have no positive or negative charge, the ionosphere can't repel them and they pass through. Then the particles reionize in the lower reaches, which indicates that the mechanism driving the loss of Mars' air is active in the lower as well as the upper atmosphere.
"We are beginning to see the links in a chain that begins with solar-driven processes acting on gas in the upper atmosphere and leads to atmospheric loss," says Bruce Jakosky, MAVEN principal investigator with the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. "Over the course of the full mission, we’ll be able to fill in this picture and really understand the processes by which the atmosphere changed over time."
Launched in November of last year from Cape Canaveral, Florida, MAVEN arrived at Mars on September 21 and has since moved to a lower orbit. Its first observations included taking ultraviolet images of the tenuous oxygen, hydrogen, and carbon coronas in the Red Planet's upper atmosphere, and creating a comprehensive map of its ozone layers.