Data obtained by the various Mars orbiters during the close fly-by of Comet Siding Spring of Mars has revealed that the comet created a new temporary layer in the planet’s atmosphere.
The European Space Agency’s Mars Express spacecraft detected an increase in electrons in Mars’ upper atmosphere, partly ionising it. This was attributed to fine cometary dust penetrating the atmosphere, which led to a meteor storm of thousands of meteors per hour. The increase in electrons led to the creation of a temporary new layer of charged particles in the ionosphere, which runs from an altitude of 120 kilometres to several hundred kilometres above. This is the first time such an event has been seen, even on Earth the extra density of electrons was measured to be five to ten times higher than normal by NASA’s Mars Reconnaissance Orbiter. Another NASA spacecraft, MAVEN, which also observed the new layer in the ionosphere, will monitor for any long-term events as it goes about its regular duties of studying Mars’ atmosphere.
MAVEN’s Imaging Ultraviolet Spectrograph was able to ascertain the species of ions that flooded into the ionosphere from the comet, the first time a comet that has come direct from the distant Oort Cloud has been sampled in this way. It detected the signal of magnesium, iron and sodium ions following the meteor shower, a signal that dominated Mars’ ultraviolet spectrum for hours afterwards, taking two days to dissipate.
The chemistry that MAVEN detected appears superficially somewhat similar to the chemistry that Rosetta is detecting at Comet 67P/C-G, though there are differences.