Meteoroid Impact Detection for Exploration of Asteroids (MIDEA): Meteoroid Impact Rates on Potential Asteroid Targets

Meteoroid impacts on asteroid surfaces produce a plasma that can be sampled by a nearby spacecraft. This plasma provides a mechanism for exploring the surface composition of asteroids using a constellation of free-flying, ultralight sensors. The requirements for detection of the expanding impact plasma is that the meteoroid is large and fast enough to produce sufficient charge, and that the asteroid surface is electrically biased so that the electrons are captured and positive ions are ejected. For a sensor positioned at a distance of 100-500 m, nanogram-sized meteoroids impacting at speeds greater than 20 km/s onto a sunlit surface can produce a detectable signal. We used NASA's Meteoroid Engineering Model (MEM) and the Grün interplanetary flux model to estimate the impact rate of meteoroids on a selection of asteroid candidates. These include near-Earth asteroids (NEAs) as well as several bodies in the main belt. Orbital trajectories were obtained using JPL's Horizons interface, and the sunward-facing meteoroid flux was computed using MEM for µg-sized meteoroids at speeds of 20 km/s or greater. The Grün model was used to scale the flux to ng-sized meteoroids. The figure below shows the maximum and minimum impact rate for each of the target bodies, ordered by their orbital semi-major axis. The NEAs have maximum rates of 0.18 to 0.30 m-2 day-1, corresponding to an impact on each square meter every 3.3 to 5.4 days. The main-belt bodies are impacted far less frequently. However, 1999 JD8, which has a high eccentricity of 0.47, has a maximum impact rate about ten times greater than Elst-Pizarro, despite having a similar semi-major axis. Because of the gossamer nature of the ultralight sensors envisioned for this exploration concept, mission duration is limited by degradation of the electronics. The impacts predicted for NEAs and for some high-eccentricity asteroids in the main belt are frequent enough to allow an asteroid to be well characterized in under a month.