The Rosetta Ion and Electron Sensor (IES) measurement of the development of pickup ions from comet 67P/Churyumov‐Gerasimenko

Abstract

The Rosetta Ion and Electron Sensor (IES) has been measuring solar wind ions intermittently since exiting from hibernation in May 2014. On 19 August, when Rosetta was ~80 km from the comet 67P/Churyumov‐Gerasimenko, which was ~3.5 AU from the Sun, IES began to see ions at its lowest energy range, ~4–10 eV. We identify these as ions created from neutral species emitted by the comet nucleus, photoionized by solar UV radiation in the neighborhood of the Rosetta spacecraft (S/C), and attracted by the small negative potential of the S/C resulting from the population of thermal electrons. Later, IES began to see higher‐energy ions that we identify as having been picked up and accelerated by the solar wind. IES continues to measure changes in the solar wind and the development of the pickup ion structure.

Statistical analysis of suprathermal electron drivers at 67P/Churyumov–Gerasimenko

“…The IES ion observations are qualitatively similar to an inactive comet shown by Goldstein et al (2015), Nilsson et al (2015a), and Broiles et al (2015). Fig.…”

“…Gas in the coma moves radially away from the nucleus, and a substantial fraction is eventually ionized through photoionization from solar ultraviolet radiation, charge exchange with the solar wind, or electron impact ionization (Cravens 1987;Cravens et al 1987;Gan & Cravens 1990). In situ observations of cometary ionospheres have been made at comets 1P/Halley (Gringauz et al 1986;Johnstone 1990;Larson et al 1992), Giacobini-Zinner Thomsen et al 1986;Zwickl et al 1986), Grigg-Skjellerup (Reme et al 1993), 19P/Borrelly (Nordholt et al 2003;Young et al 2004), and recently at 67P/Churyumov-Gerasimenko (67P) Burch et al 2015;Clark et al 2015;Edberg et al 2015;Goldstein et al 2015;Nilsson et al 2015a;Behar et al 2016).…”

RPC observation of the development and evolution of plasma interaction boundaries at 67P/Churyumov-Gerasimenko

“…This causes low-energy electrons to be deflected away from the spacecraft, preventing LAP from providing accurate densities of electrons with energies lower than 20 eV. However, a strong negative spacecraft potential accelerates newly produced ions into IES and ICA providing an opportunity to measure ions at the earliest stages of the pickup process (Goldstein et al 2015;Nilsson et al 2015a,b).…”

Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument

“…Locally produced water ions, accelerated into the instrument by a negative spacecraft potential, were first detected by the Rosetta Ion and Electron Sensor (RPC-IES) on 19 August 2014 at a distance of ∼80 km from the nucleus [Goldstein et al, 2015]. These ions have also been detected by RPC-ICA, starting on 21 September 2014 at a distance of 28 km from the nucleus.…”