New paper from Journal of Geophysical Research- Planets (JGR-P), December 2025 (vol. 130 #12):
Lawrence, W. M. Ehlmann, B. Phyllosilicate Infrared Spectral Features as Tracers of Aqueous Alteration in CM Chondrites and Implications for Remote Sensing of Hydrated Asteroids 2025JE009377
Clays (or technically, phyllosilicates) are everywhere. The carbonaceous-chondrite meteorites contain various amounts of clay, if for no other reason that the CV, CK chondrite groups, etc. often contain mixed fragments of the clay-rich groups CM and CI, etc. And then, Mars, Earth, and Earth’s achondrite satellite receive a rain of meteorites, including CMs, CIs, and the dust produced from these (which contain clay particles). In other words: we live in a damp, phyllosilicate-rich star system.
To be specific: the CM and CI chondrite meteorite groups are largely clay (CIs are ~80% phyllosilicate matrix), and ‘lesser’ carbonaceous groups like CR and some ungrouped carbonaceous meteorites will sometimes have nontrivial clay contents. Since the water in phyllosilicates is bound at the atomic level, this water content survives gentle and moderate impacts. If one considers that the influx of micrometeorites and dust particles is over one order of magnitude larger than the mass flux of human-scale, macro-meteorites, and if one considers that micrometeorites and dust particles are subject to the Poynting-Robertson effect, circularizing and shrinking their orbits, then one reaches a strange conclusion: we are being steadily ‘bombarded’, so to speak, by damp clay particles. In other words: the inner Solar System is being moisturized by asteroid shavings.
Lawrence et al. are well aware. Given that we have samples of CI, CM, CR meteorites etc., can we use their spectral appearance to look for asteroids that might be parent bodies of CI/CM/CR/whatever? A first cut would presume that the carbonaceous asteroids are the parents of carbonaceous meteorites, chipped off by impacts. Sure enough, the Hayabusa2 mission found that Ryugu material looks like CI meteorite material. But the relationship is imperfect; there are plenty of carbonaceous asteroids, in multiple subtypes within the C-Complex of asteroids (true C-type, and Cb, Ch, etc.). Why do some carbonaceous asteroids look like Ryugu (and thus, the CI meteorites) but some do not? If not, what meteorites do they correspond with? Again, we can make a first guess: some asteroids have their surfaces heavily altered by space weathering, while some have ‘fresher’ (on geologic timescales) surface material. But this relationship, too, is imperfect. Space weathering of carbonaceous asteroids does not behave like the ordinary-chondrite asteroids and Earth’s basaltic, baked satellite. And Haya2 and OSIRIS-REx seem to indicate that Bennu’s space weathering is merely an older, more advanced version of Ryugu weathering- this is a new finding and still being studied.
At the very least, we’d like to know which asteroids are wetter than others. Water, a source of propellant and other mineral wealth, makes water-rich asteroids inherent destinations for asteroid mining. But we can’t just head for the asteroids without a map, can we?