In the October Astronomy and Astrophysics (vol. 690… a big one this month):
Wang, Z. Lin, H. Ye, B. et al. Near-infrared spectral behavior of space-weathered olivine with varying iron content A138 10.1051/0004-6361/202450888
Beniyama, J. Sergeyev, A. V. Tholen, D. J. et al. Rotation state, colors, and albedo of the mission-accessible tiny near-Earth asteroid 2001 QJ142 A180 10.1051/0004-6361/202451414
Jin, S. Ishiguro, M. Geem, J. Naito, H. et al. New evidence supporting past dust ejections from active asteroid (4015) Wilson–Harrington A193 10.1051/0004-6361/202451225
Athanasopoulos, D. Hanuš, J. Avdellidou, C. et al. Spin states of X-complex asteroids in the inner main belt – I. Investigating Athor and Zita collisional famili… A215 202451363
Biver, N. Bockelée-Morvan, D. Handzlik, B. et al. Chemical composition of comets C/2021 A1 (Leonard) and C/2022 E3 (ZTF) from radio spectroscopy and the abundance of HCOOH and A271 202450921
Mastropietro, M. Kim, Y. Hsieh, H. H. et al. Activity of main-belt comet 324P/La Sagra
A298 202451090
de la Fuente Marcos, de la Fuente Marcos, R. C. Aarseth, S. J. Ejected from home: C/1980 E1 (Bowell) and C/2024 L5 (ATLAS) A395 202451920
Attree, N. Gutiérrez, P. Groussin, O. et al. Varying water activity and momentum transfer on comet 67P/Churyumov-Gerasimenko from its non-gravitational forces and torques A82 202450728
Olivine- one of the basic building blocks of silicate bodies. That is, planets (including the cores of gas and ice worlds), asteroids, and to an extent comets. Olivine is also just detectable in standard (silicon chip) instruments, with an absorption band at ~0.9 micrometers. We want to gauge the silicate bodies by their building blocks, and thus understand what olivine’s doing, including mixtures and contaminants. Wang et al. show us various flavors of olivine, very helpful, thanks.
There are tens of thousands of Near-Earth Asteroids (NEAs). If even a percentage of a percentage have favorable qualities, and then highly-favorable qualities, that means a NEA for whatever criterion your heart desires. Going by the metric of mission-favorable orbits (NEAs easy to access with a probe), we have databases like MANOS and NHATS that filter for mission-target-able NEAs (plural, of course). For one particular ‘nearby’ (in propulsive terms) asteroid, Beniyama et al. now characterize that asteroid.
“Comet” Wilson-Harrington is one of the prototype transition objects. Look too quickly and it seems like an asteroid. The rising count of transition objects would eventually lead to the use of “Small Solar System Bodies” (SSSBs) as a term that removes the asteroid-comet ambiguity. It’s in these grey areas that we have room to play, pedagogically- interesting things happen within the transition zone. In this case, what’s the Wilson-Harrington history- is it sputtering out? Temporarily quiet? Something else?
X-complex asteroids are a catchall category- they are neither the dominant classes (C-complex and S-complex), and itself breaking down into the very different E-, M-, and P-subtypes. At the very minimum, we can trace back families (the asteroids split by collision, from some parent asteroid) on the assumption that common-formed bodies have a common composition. (A decent enough assumption for P- and some E-, automatically suspect for M-type. M-type asteroids are the cores of differentiated bodies, where are the mantles and crusts?)
…and of course, the question of comet composition (itself not automatically assumed the same for nucleus vs. coma/tail) is still not secure…
To circularize: there are asteroids, there are comets… and there are astero-comets and comsteroids. Main-Belt Comets fall in our grey area. What is going on with these inner-Solar-System, ice-bearing, asteroid-neighboring objects? 324P/La Sagra, one of the earliest to be discovered by humanity, continues to teach us what we didn’t even know that we didn’t know.
The question of “asteroid” vs. “comet” vs. transition object is an open question- again, we don’t know what we don’t know.