Energetic ions in the Venusian system: Insights from the first Solar Orbiter flyby


The Solar Orbiter flyby of Venus on 27 December 2020 allowed for an opportunity to measure the suprathermal to energetic ions in the Venusian system over a large range of radial distances to better understand the acceleration processes within the system and provide a characterization of galactic cosmic rays near the planet. Bursty suprathermal ion enhancements (up to ~10 keV) were observed as far as ~50 RV downtail. These enhancements are likely related to a combination of acceleration mechanisms in regions of strong turbulence, current sheet crossings, and boundary layer crossings, with a possible instance of ion heating due to ion cyclotron waves within the Venusian tail. Upstream of the planet, suprathermal ions are observed that might be related to pick-up acceleration of photoionized exospheric populations as far as 5 RV upstream in the solar wind as has been observed before by missions such as Pioneer Venus Orbiter and Venus Express. Near the closest approach of Solar Orbiter, the Galactic Cosmic Ray (GCR) count rate was observed to decrease by approximately 5 percent, consistent with the amount of sky obscured by the planet, suggesting a negligible abundance of GCR albedo particles at over 2 RV . Along with modulation of the GCR population very close to Venus, the Solar Orbiter observations show that the Venusian system, even far from the planet, can be an effective accelerator of ions up to ~30 keV. This paper is part of a series of first papers from the Solar Orbiter Venus flyby; Volwerk et al. (2021) further discusses the magnetic field observations, Hadid et al. (2021) focuses on observations from the radio and plasma waves instrument, and Dimmock et al. (2021) focuses on characterizing the bow shock.