Charged Atmosphere

Artist’s rendering of the MAVEN spacecraft and the limb of Mars.

NASA Goddard Space Flight Center

The upper atmosphere of Earth is constantly bombarded by tiny meteoroids known as interplanetary dust particles. As these particles undergo solar radiation and react with other molecules in the atmosphere, they vaporize and leave a residue of metallic ions, positively charged particles of such elements as magnesium, iron, and sodium. The resulting ionosphere has been observed above Earth since 1963. Because the dust that forms the ions is found throughout the solar system, a similar process has been assumed to occur on every planet or moon with an atmosphere, but definitive proof has been lacking.

NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, which orbits that planet, has now confirmed that the ions exist above Mars. They were first detected in 2014, in connection with the close approach of a comet to Mars. More recently, MAVEN’s mass spectrometer confirmed their presence on a constant, long-term basis.

Astrophysicist Joseph Grebowsky of NASA’s Goddard Space Flight Center in Maryland led the study of the metallic ions. His team found significant differences in the behavior of metallic ions in the Martian atmosphere as compared with those in Earth’s. 

For example, on Earth, the ions of various atmospheric metals sort themselves into layers, as a function of high altitude winds and the planet’s magnetic field. On Mars, despite the absence of a magnetic field, scientists expected that gravity would similarly separate the heavier iron ions and lighter magnesium ions into separate layers by weight. In fact, though, the various metals are well mixed. In a few isolated areas, separate layers do form even though remanent magnetic fields appear too weak to be the formation mechanism.

While these findings support the assumption that other planets and moons with atmospheres have metal ions present, the models used to describe the transport and layering of ions on Earth do not appear adequate to account for conditions on Mars. Why mixing occurs and what causes the isolated layers are two of several puzzles yet to be unraveled, says Grebowsky. Either “another transport process needs to be included along with collisional/turbulent diffusion or a new mixing process needs to be defined for the metal ions.” (Geophysical Research Letters)