A transient enhancement of Mercury's exosphere at extremely high altitudes inferred from pickup ions.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32994408.
- Also identified by DOI 10.1038/s41467-020-18220-2 and PMC identifier 7525509.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Mercury has a global dayside exosphere, with measured densities of 10<sup>-2</sup> cm<sup>-3</sup> at ~1500 km. Here we report on the inferred enhancement of neutral densities (<10<sup>2</sup> cm<sup>-3</sup>) at high altitudes (~5300 km) by the MESSENGER spacecraft. Such high-altitude densities cannot be accounted for by the typical exosphere. This event was observed by the Fast-Imaging Plasma Spectrometer (FIPS), which detected heavy ions of planetary origin that were recently ionized, and "picked up" by the solar wind. We estimate that the neutral density required to produce the observed pickup ion fluxes is similar to typical exospheric densities found at ~700 km altitudes. We suggest that this event was most likely caused by a meteroid impact. Understanding meteoroid impacts is critical to understanding the source processes of the exosphere at Mercury, and the use of plasma spectrometers will be crucial for future observations with the Bepi-Colombo mission.