Evidence for small‐scale collisionless shocks at the Moon from ARTEMIS

Abstract

AbstractARTEMIS observes structures near the Moon that display many properties commonly associated with collisionless shocks, including a discontinuity with downstream compression of magnetic field and density, heating and wave activity, and velocity deflections away from the Moon. The two‐probe ARTEMIS measurements show that these features do not exist in the pristine solar wind and thus must result from lunar influences. Discontinuity analyses indicate mass flux and heating across the boundary, with the normal velocity dropping from supermagnetosonic to submagnetosonic across the discontinuity. The shock location with respect to crustal magnetic fields suggests a causal relationship, implying that solar wind protons reflected from crustal fields may produce the observed structures. These observations may indicate some of the smallest shocks in the solar system (in terms of plasma scales), driven by solar wind interaction with magnetic fields on the order of the ion gyroradius and inertial length.