Impact Ejecta and Gardening in the Lunar Polar Regions

Abstract

The Moon is continually bombarded by interplanetary meteoroids. While many of the meteoroid sources are near the ecliptic plane, a significant population of high‐inclination meteoroids exists at 1 au that bombards the lunar polar regions. Building on previous measurements of the response of the lunar impact ejecta cloud to known meteoroid sources, we develop an ejecta model for the entire lunar surface by incorporating the high‐inclination sources. We find that the polar regions of the Moon experience similar quantities of impact ejecta production as the equator. Due to the enhanced impactor fluxes near the equator and at high latitudes on the dawn side, lunar regolith is preferentially distributed to the mid to high‐latitude regions over long timescales, providing a pathway to mix regolith from different regions. We find impact ejecta yields at the Moon to be significantly lower than the Galilean moons, suggesting meteoroids deliver more energy to the local regolith and can be an important driver in the evolution of volatiles near the lunar surface. Additionally, we find that a polar orbiting spacecraft equipped with a dust analyzer can measure appreciable quantities of lunar ejecta near the poles to constrain the water content in the polar regions.

The Young Age of the LAMP‐observed Frost in Lunar Polar Cold Traps

“…More detailed analysis of the impact ejecta emission cone indicates that the grains are released in a 10°cone (Bernardoni et al, 2019;Szalay et al, 2019), and thus, grains with speeds up to 305 m/s would have a range <20 km and remain in the crater, corresponding to about 13 % of the total particulate ejecta produced by the impact. Figure 1 compares the various surface emission rates as a function of temperature.…”

Using dust shed from asteroids as microsamples to link remote measurements with meteorite classes

“…; Szalay et al. 2019b). Therefore, a harder asteroidal surface could produce significantly higher ejecta yields than the Moon's regolith surface, from which these predictions were derived.…”

“…Recently-visited asteroids Bennu and Ryugu have an overall larger grain size and more exposed hard surfaces than the Moon's regolith (Lauretta et al, 2019;Watanabe et al, 2019). Impact ejecta observations and comparison to impactor models suggest that the Moon's fine regolith surface may have a lower yield than an equivalent solid surface of the same material, where a larger fraction of impact energy may get partitioned to local heating of the regolith instead of into the kinetic energy of ballistic ejecta (Szalay et al, 2019b, Pokorny et al, 2019. Therefore, a harder asteroidal surface could produce significantly higher ejecta yields than the Moon's regolith surface, from which these predictions were derived.…”

Assessing the Roughness Properties of Circumpolar Lunar Craters: Implications for the Timing of Water‐Ice Delivery to the Moon

“…Specifically, the ongoing rates of plasma sputtering and meteoric impact vaporization and ejection on the Moon suggest that the ice present at the surface or near‐surface of regolith particles (as sensed by LAMP to a depth of <1 μm) must be <2,000 years old (Farrell et al, 2019). Relatively young surface ice can be delivered to the Moon from micrometeorite bombardment (Ong et al, 2010; Pokorný et al, 2019; Szalay et al, 2019) or formed in situ from the ongoing interactions between solar wind protons and oxygen in the lunar regolith (e.g., Crider & Vondrak, 2000; Dyar et al, 2010). Ice delivered during the Eratosthenian or Copernican eras is not predicted to be volcanic in origin, given that the bulk of lunar volcanism occurred prior to these eras (e.g., Needham & Kring, 2017).…”