New suprathermal proton population around the Moon: Observation by SARA on Chandrayaan‐1

Abstract

We report a new population of suprathermal H+ (∼1.5–3 times the solar wind energy) around the Moon observed by Solar Wind Monitor (SWIM)/Sub‐keV Atom Reflecting Analyzer (SARA) on Chandrayaan‐1. These ions have large initial velocity (>100 km s−1) and are observed on the dayside, near the terminator, and in the near‐wake region (100–200 km above the surface), when the Moon is located outside Earth's bow shock. Backtracing suggests that the source is located >500 km above the dayside lunar surface. Possible sources considered for these ions are ionization of backscattered lunar energetic neutral hydrogen atoms, ionization of lunar exospheric hydrogen, inner source pickup ions, interstellar pickup ions, ionization of neutral solar wind, and solar wind H+ reflected from Earth's bow shock. The comparison of the observed flux (density) with that expected from these sources and the velocity distribution suggests that an additional source is required to explain the population.

In situ observations of ions and magnetic field around Phobos: the mass spectrum analyzer (MSA) for the Martian Moons eXploration (MMX) mission

“…The backscattering of the solar wind was also observed around Phobos (Futaana et al 2010a). The solar wind not only bombards the dayside surface of the Moon, but also intrudes the wake region because of electromagnetic effects (Futaana et al 2010b;Nishino et al 2009Nishino et al , 2010Nishino et al , 2013Dhanya et al 2017). In addition, some of the solar wind is reflected in the Earth's bow shock and irradiates the nightside of the Moon (Nishino et al 2017).…”

In Situ Observations of Ions and Magnetic Field Around Phobos: The Mass Spectrum Analyzer (MSA) for the Martian Moons eXploration (MMX) Mission

“…The back scattering of the solar wind was also observed around Phobos (Futaana et al 2010a). The solar wind not only bombards the dayside surface of the Moon but also intrudes the wake region because of electromagnetic effects (Futaana et al, 2010b;Nishino et al, 2009Nishino et al, , 2010Nishino et al, , 2013Dhanya et al, 2017). In addition, some of the solar wind is reflected in the Earth's bow shock and irradiate the nightside of the Moon (Nishino et al, 2017).…”

First Observation of Transport of Solar Wind Protons Scattered From Magnetic Anomalies Into the Near Lunar Wake: Observations by SARA/Chandrayaan‐1

“…The indirect transport include the entry of solar wind scattered from dayside lunar surface to the near wake region (Nishino, Fujimoto, et al, ; Wang et al, ) and also the solar wind scattered from Earth's bow shock (Nishino et al, ). Further, new population of protons is found in the near lunar wake whose source(s) is(are) yet to be identified (Dhanya et al, , ; Vorburger et al, ).…”

“…The indirect transport include the entry of solar wind scattered from dayside lunar surface to the near wake region Wang et al, 2010) and also the solar wind scattered from Earth's bow shock (Nishino et al, 2017). Further, new population of protons is found in the near lunar wake whose source(s) is(are) yet to be identified (Dhanya et al, 2016(Dhanya et al, , 2017Vorburger et al, 2016). 10.1029/2018GL079330 observational evidence so far for such a process, and also, the energy and flux of such a population in near wake are not known. In the following, we demonstrate the first observational evidence for this process.…”