Quite the interesting Planetary and Space Science for July (volume 246):
Alvarez, S. R. Sosa Oyarzabal, A. Comet P/2003 T12 (SOHO): A possible fragment o… art. 105902
.2024.105902
Gramigna E. Lasagni Manghi R. Zannoni M. et al. The Hera Radio Science Experi… art. 105906 .2024.105906
Halim, S. H. Crawford, I. A. Collins, G. S. Assessing the survival of carbonaceous cho… art. 105905
.2024.105905
Alvarez Sosa Oyarzabal is a reasonable dynamical/parentage hypothesis. Gramigna et al. is a typical writeup of an instrument on a spacecraft, and its mission plan. But…
The full title of Halim et al. 2024 is “Assessing the survival of carbonaceous chondrites impacting the lunar surface as a potential resource.” Short: Not a good resource, just like the Earth’s moon in general. The lunar surface in question was depleted- severely- by being double-differentiated. Earth’s crust baked off its precious volatiles when it was young and hot. Then a giant impactor knocked off crust and mantle material to form Earth’s moon. That second crust was, again, baked of its remaining volatiles while young (for its own chronology) and hot. In other words, lunar rock is not just more Earth rock, it’s bad Earth rock.
Still, what if asteroids or comets (or ast-ets) landed, bringing back fresh material? Ha, comets don’t land. Comets, with severely eccentric and inclined orbits, have steep crossing vectors, and thus, extreme kinetic energy of impact- that’s impact, as in hypervelocity impact, not landing. Such hypervelocity impacts reduce the impact site, let alone the impactor, to hot, baked rock-splash. No water, or similar volatiles, remain because they’ve been vaporized by the impact energy, and lost back to space. Halim et al. confirm this by analysis (as if prior works had not already confirmed each other). Still, Halim and colleagues hypothesized that asteroidal water, assumed bound in serpentinite and other phyllosilicates, might survive, along with carbon and nitrogen, thereby “un-depleting” the lunar surface.
Result: neither comets, and not most asteroids either, can deliver more than trivial H2O, C, and N to a barren moon. The exception is an asteroid of large size, slow impact speed, and quite shallow impact angle. Halim et al. continue: the odds of this happening are “low probability”- perhaps 5 such impacts over the history of the Solar System.
Asteroids have water, in multiple forms. And carbonaceous chondrites, like Ryugu and Bennu, have organics, with C and N. The moon has… fanboys, led on by publicity. We have plenty of fanboys and publicity, which means they’re devalued.