Plasma-neutral gas interactions in various space environments: Assessment beyond simplified approximations as a Voyage 2050 theme

Abstract

In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task requires addressing the following fundamental questions: (A) How and by how much do plasma-neutral gas interactions influence the re-distribution of externally provided energy to the composing species? (B) How and by how much do plasma-neutral gas interactions contribute toward the growth of heavy complex molecules and biomolecules? Answering these questions is an absolute prerequisite for addressing the long-standing questions of atmospheric escape, the origin of biomolecules, and their role in the evolution of planets, moons, or comets, under the influence of energy sources in the form of electromagnetic and corpuscular radiation, because low-energy ion-neutral cross-sections in space cannot be reproduced quantitatively in laboratories for conditions of satisfying, particularly, (1) low-temperatures, (2) tenuous or strong gradients or layered media, and (3) in low-gravity plasma. Measurements with a minimum core instrument package (< 15 kg) can be used to perform such investigations in many different conditions and should be included in all deep-space missions. These investigations, if specific ranges of background parameters are considered, can also be pursued for Earth, Mars, and Venus.

Plasma-neutral interactions in the lower thermosphere-ionosphere: The need for in situ measurements to address focused questions

“…It is noted in particular that no current or prior set of observations combines simultaneous and co-spatial measurements of horizontal1 and vertical neutral winds together with electric currents. In addition, estimates of collision rates are currently based on cross-sections from ground laboratory experiments, which, however, cannot reproduce the complex LTI environmental plasma, neutral and electromagnetic conditions (Yamauchi et al, 2022). At small scales, strong flow shears and steep gradients can drive a variety of instabilities and turbulence in both plasma and neutral gas, the understanding of which is an outstanding challenge in space physics community.…”

Plasma-Neutral Interactions in the Lower Thermosphere-Ionosphere: The need for in situ measurements to address focused questions

“…In particular, comprehensive measurements of neutral winds are critical in advancing current knowledge of LTI dynamics and, presently, such measurements are sparsely distributed in time and space [10,11]. Furthermore, estimates of collision rates are currently based on cross-sections from ground laboratory experiments, which, however, cannot reproduce the complex LTI environmental plasma, neutral and electromagnetic conditions [12]. At small scales, strong flow shears and steep gradients can drive a variety of instabilities and turbulence in both plasma and neutral gas, the understanding of which is an outstanding challenge in space physics community.…”