Göttingen 2025 – wissenschaftliches Programm

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EP: Fachverband Extraterrestrische Physik

EP 10: Poster Session

EP 10.19: Poster

Donnerstag, 3. April 2025, 11:00–12:30, ZHG Foyer 1. OG

Helium at the terrestrial planets - recent spacecraft observations — •Markus Fränz and Harald Krüger — Max-Planck-Institut fuer Sonnensystemforschung, 37077 Goettingen, Germany

The Sun is a primary source of Helium in the inner solar system. At the terrestrial planets radio active decay can also contribute to the Helium budget in the exospheres. The third source of Helium is the interstellar neutral gas. Recent missions to planet Mercury are giving new interesting insights on the role of the different sources. The MESSENGER spacecraft was launched in 2004, and between March 2011 and April 2015 it was the first spacecraft in orbit around Mercury. The FIPS instrument on board MES- SENGER measured the ion composition in the vicinity of Mercury and in the inner solar system. We aim to determine the origin of He+ ions in the inner solar system and in the environment of Mercury, continuing earlier work by Gershman et al. (2013). We have analyzed measurements of He+ and He2+ ions made by the FIPS instrument during the interplanetary cruise phase of MESSENGER and its entire orbital mission at Mercury. We de- termined the spatial distributions of He+ ions in the regions sampled by MESSENGER during that period and compare the spectra to a similar observation by the MPPE-MSA instrument onboard BepiColombo. We here consider two possible sources of He+: (1) interstellar neutral helium ionized close to Mercury and (2) solar He2+ ions converted close to or at the surface of Mercury. We also compare the observed densities with a simple model of the ionization of the interstellar helium flow.

Keywords: solar wind; interstellar gas; planet Mercury