Detection and characterization of wind-blown charged sand grains on Titan with the DraGMet/EFIELD experiment on Dragonfly

Audrey Chatain (1, 2) , Alice Le Gall (1) , Jean-Jacques Berthelier (1) , Ralph D. Lorenz (3) , Rafik Hassen-Khodja (1) , Jean-Pierre Lebreton (4) , Tom Joly-Jehenne (5) , Grégoire Déprez (6)

1 PLANETO - LATMOS
2 Departamento de Fisica Aplicada [Bilbao]
3 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
4 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
5 ENS Paris Saclay - Ecole Normale Supérieure Paris-Saclay
6 ESTEC - European Space Research and Technology Centre

The EFIELD instrument is part of the geophysics and meteorology sensor package DraGMet on the Dragonfly mission, which will explore the surface of Titan in the mid-2030s. EFIELD consists of two electrodes designed to passively record the AC electric field at each Dragonfly landing site. The probes will be mounted at two different locations on the body of the rotorcraft lander. The exploration zone of the Dragonfly mission will mostly consist of dune fields, covered with sand grains. Little is known on the properties of these grains, although Cassini-Huygens observations suggest they are mostly made of organic material produced by Titan’s atmospheric photochemistry and evolved at the surface. Little is known also about dune formation and, in general, about the transport of sediments by winds on Titan. This latter much depends on inter-particle forces and therefore on whether grains are charged (e.g. by friction) or not. In this paper, we demonstrate that the EFIELD experiment can bring new insights on these questions. We have developed a hydrodynamic-electrostatic model to simulate the trajectory of a wind-blown charged sand grain in the vicinity of an idealized EFIELD probe (an electronically insulated probe in a neutral open space) and to predict how such a grain flying close to the probe would affect its potential. We show that, in some conditions, the resulting perturbation will be strong enough to be detected by the EFIELD probe. More specifically, we find that the detection of typical charged wind-blown grains (200 μm in size) on Titan requires an instrument standard deviation noise inferior to 1 mV, though occasional larger grains flying close to one electrode could be detected with a higher noise level. Furthermore, we propose a method to retrieve information on the charge and velocity of wind-blown charged grains detected by the EFIELD experiment. This method well applies for cases where the particle trajectory can be regarded as quasi-linear. We validate our inversion approach on both synthetic and experimental data obtained with a laboratory prototype of the EFIELD experiment. Such approach was developed with assumptions on the accommodation and electronic design of the EFIELD experiment but can be adapted to account for the final architecture of the experiment

Domaines: Planète et Univers [physics]

Audrey Chatain, Alice Le Gall, Jean-Jacques Berthelier, Ralph D. Lorenz, Rafik Hassen-Khodja, et al.. Detection and characterization of wind-blown charged sand grains on Titan with the DraGMet/EFIELD experiment on Dragonfly. Icarus, 2023, 391 (february), pp.115345. ⟨10.1016/j.icarus.2022.115345⟩. ⟨insu-03844450⟩