Mars appears to be blasting material out of its atmosphere, much as the sun launches explosive coronal mass ejections, even though the Red Planet has no overall magnetic field.
When the magnetic fields in ionised gas, called plasma, around a star like our sun suddenly change direction or snap in two, there can be a large burst of energy that launches a parcel of plasma into space, known as a coronal mass ejection.
Astronomers have observed similar conditions in Mars鈥檚 plasma-filled upper atmosphere, the ionosphere, even though the planet has only pockets of magnetic field produced in its crust, rather than a global magnetic field like the sun. However, mass ejections from Mars had never been seen.
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Now, at the Institute of Earth Sciences in Taiwan and his colleagues have spotted three explosive mass ejections from Mars鈥檚 ionosphere using data from NASA鈥檚 Mars Atmosphere and Volatile Evolution satellite, which happened in 2014, 2016 and 2019.
Unlike mass ejections from the sun, which are dense enough to reflect sunlight and so be seen from Earth, Mars鈥檚 mass ejections are harder to catch sight of, so the researchers instead looked for areas in the ionosphere where there appeared to be an absence of plasma, called density cavities.
Lee and his colleagues think Mars鈥檚 mass ejections are caused by interactions between its lumpy magnetic field and the solar wind, a constant stream of charged particles. The stream makes the planet鈥檚 magnetic field lines snap and blast out plasma.
The ejections are orders of magnitude smaller than those from the sun, so probably wouldn鈥檛 affect satellites or Earth, says Lee.
If this is happening in Mars鈥檚 atmosphere, it could mean similar processes are occurring in other planets that also lack global magnetic fields, such as Venus, says at the University of Reading, UK. 鈥淢y naive understanding would be that the solar wind interaction is going to be pretty simple in those cases, because it鈥檚 just impacting on the upper atmosphere, but that鈥檚 not the case. Clearly, there is an interaction with the crustal field that makes it more complex than you might first think.鈥�
Nature Astronomy
