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Pickup ions from a meteor impact on Mercury

30 September 2020

A study recently published in Nature Communications, and co-authored by CPS colleague Prof Andrew Coates, has inferred a meteoroid impact on Mercury from the pickup ions of the vaporized surface soil observed with the NASA Messenger spacecraft.

Illustration of the Mercury impact event

Former UCL-MSSL / CPS PhD student Jamie Jasinski, now at JPL, led this study in Nature Communications, with other ex-UCL/CPS colleagues (Leonardo Regoli and Tom Nordheim), as well as Prof Andrew Coates (UCL MSSL / CPS). 

A sudden factor ~10,000 increase in the density of sodium and other heavy particles in Mercury's exosphere was inferred from NASA Messenger data.  This was due to a meteor impact on Mercury's surface, which threw up neutral material including sodium atoms into Mercury's environment. This sudden increase in neutral particle density extended outside Mercury's magnetosphere and bow shock. The neutral particles became ionized in sunlight and then interacted with the solar wind, a plasma of charged particles. The new ions become 'picked up' in the solar wind electric and magnetic fields, then gyrate around the magnetic field and escape the planet, as at a comet. We analysed the flow of these ions using techniques developed at UCL by Prof Andrew Coates for comets Halley, Grigg-Skjellerup & 67P, and also used by us at other bodies like Europa, Ganymede, Titan, Enceladus, Rhea, Dione, Venus and Mars, showing that the ions are in the early phase of the ion pickup process. As far as we know, this is the first time a meteor impact has ever been observed at another planet beyond the Earth-Moon system, reminding us of comet Shoemaker-Levy 9 at Jupiter in 1994.

Image

  • Illustration of the event: A schematic (not to scale) of the pickup ion process occurring during our observed transient exosphere event. hv shows photons, which ionize the planetary atoms originating from a plume caused by a meteroid impact event. These ions are then picked up by the solar wind and gyrate around the interplanetary magnetic field. Credit: Jasinski et al.

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