NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has made the first detection of the continuous presence of iron, magnesium, and sodium ions in the electrically charged upper atmosphere (ionosphere) of the Red Planet.
MAVEN is exploring Mars’ upper atmosphere in detail to understand how Mars changed from a wet planet early in its history to the cold, dry world we see today. Image credit: NASA’s Goddard Space Flight Center.
Sounding rockets, radar and satellite measurements have detected metal ion layers high in the atmosphere above Earth.
There’s also been indirect evidence for metal ions above other planets in our Solar System.
When spacecraft are exploring these worlds from orbit, sometimes their radio signals pass through the planet’s atmosphere on the way to Earth, and sometimes portions of the signal have been blocked.
This has been interpreted as interference from electrons in the ionosphere, some of which are thought to be associated with metal ions.
However, long-term direct detection of the metal ions by MAVEN is the first conclusive evidence that these ions exist on another planet.
“MAVEN has detected iron (Fe+), magnesium (Mg+), and sodium (Na+) ions in the upper atmosphere of Mars over the last two years using its Neutral Gas and Ion Mass Spectrometer instrument, giving us confidence that the metal ions are a permanent feature,” said Dr. Joseph Grebowsky, a researcher at NASA’s Goddard Space Flight Center, and his colleagues from the United States and UK.
According to the team, the metal comes from a constant rain of tiny meteoroids onto the planet.
When a high-speed meteoroid hits the Martian atmosphere, it vaporizes. Metal atoms in the vapor trail get some of their electrons torn away by other charged atoms and molecules in the ionosphere, transforming the metal atoms into electrically charged ions.
“Observing metal ions on another planet gives us something to compare and contrast with Earth to understand the ionosphere and atmospheric chemistry better,” said Dr. Grebowsky, who is the lead author of a paper on this research published online in the journal Geophysical Research Letters on April 10.
“Because metallic ions have long lifetimes and are transported far from their region of origin by neutral winds and electric fields, they can be used to infer motion in the ionosphere, similar to the way we use a lofted leaf to reveal which way the wind is blowing.”
Dr. Grebowsky and co-authors also found that the metal ions behaved differently on Mars than on Earth.
Our planet is surrounded by a global magnetic field generated in its interior, and this magnetic field together with ionospheric winds forces the metal ions into layers.
However, Mars has only local magnetic fields fossilized in certain regions of its crust, and the authors only saw the layers near these areas.
“Elsewhere, the metal ion distributions are totally unlike those observed at Earth,” Dr. Grebowsky said.
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J.M. Grebowsky et al. Unique, non-Earthlike, meteoritic ion behavior in upper atmosphere of Mars. Geophysical Research Letters, published online April 10, 2017; doi: 10.1002/2017GL072635
This article is based on a press-release from the National Aeronautics and Space Administration.
