A transient enhancement of Mercury's exosphere at extremely high altitudes inferred from pickup ions.

ABSTRACT: Mercury has a global dayside exosphere, with measured densities of 10^-2?cm^-3 at ~1500?km. Here we report on the inferred enhancement of neutral densities (<10²?cm^-3) 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.

SUBMITTER: Jasinski JM 

PROVIDER: S-EPMC7525509 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature