Assessing the survival of carbonaceous chondrites impacting the lunar surface as a potential resource

The Moon offers a wide range of potential resources that may help sustain a future human presence, but it lacks indigenous carbon (C) and nitrogen (N). Fortunately, these elements will have been delivered to the Moon’s surface by carbonaceous chondrite (CC) asteroid impactors. Here, we employ numerical modelling to assess the extent to which these materials may have sufficiently survived impact with the lunar surface to be viable sources of raw materials for future exploration. We modelled the impact of a 1 km diameter CC-like asteroid, considering impact velocities between 5 and 15 km s-1, and impact angles between 15 and 60° to the horizontal. The most favourable conditions for the survival of C-rich, and especially N-rich materials, are those with the lowest impact velocities (≤10 km s-1) and impact angles (≤15°). Impacts with velocities >10 km s−1 and angles >30° were found not to yield any significant amount of surviving solid material, where bulk survival is defined as material experiencing temperatures less than the impactor material’s estimated melting temperature (∼2100 K, based on a commonly adopted Equation of State for serpentine). Importantly, oblique and low velocity impacts result in concentrations of unmelted projectile material down-range from the impact site. For the canonical 1 km-diameter CC impactor considered here, with an impact angle ≤15° and velocity ≤10 km s-1, this results in ∼109 - 1010 kg of C and ∼108 - 109 kg of N being deposited a few tens of km down-range from the impact crater, where it might be accessible as a potential resource. Such low-velocity and oblique impacts have a low probability - we estimate that only ∼5 such impacts may have occurred on the Moon in the last 3 billion years (the number of impacts of smaller impactors will have been higher, but they will concentrate lower masses of potential resources). As the estimated C and N concentrations from such impacts greatly exceed those expected for ices within individual permanently shadowed polar craters, searching for these rare impact sites may be worthwhile from a resource perspective. We briefly discuss how this might be achieved by means of orbital infra-red remote-sensing measurements.