Comment on "The Dominant Role of Energetic Ions in Solar Wind Interaction With the Moon" by Omidi et al.

Omidi et al. (2019) recently published a case study analysis of the lunar wake crossing by the ARTEMIS P2 spacecraft that occurred on 24 June 2015 by comparing P2 observations of plasma and magnetic fields in the lunar wake with a hybrid plasma model using upstream plasma conditions measured by ARTEMIS P1. As presented in Omidi et al., the ARTEMIS P2 ion moments during the lunar wake crossing show anomalously high temperatures and low velocities. This is due to both the lack of subtraction of background counts from penetrating radiation and the application of moment analysis during times when no ion flux was observed by ARTEMIS P2. Additionally, the hybrid results show large discrepancies with the ARTEMIS data, from which Omidi et al. concluded that an additional smaller population of suprathermal ions was required to accurately reproduce the ARTEMIS observations. This conclusion is at odds with previous investigations and, thus, deserves further study. Here we have used the Amitis hybrid plasma model to simulate the lunar wake with upstream plasma conditions determined from the ARTEMIS P1 reference observations, identical to those used in the Omidi et al. "Run-0" hybrid model. We found that the Amitis hybrid model can successfully reproduce the structure of the lunar wake and the ARTEMIS P2 observations with good fidelity, without the inclusion of any additional high energy ion populations. We therefore conclude that energetic ions do not dominate the structure and behavior of the lunar wake, in contrast to the conclusions of Omidi et al.