This month’s Astronomical Journal (vol. 169 Number 2) is all about the (quasi-) comets:
Kasuga, T. Comet 289P/Blanpain: Near perihelion Activity and the Phoenicids 54 ad95fd
Kurlander, J. A. Holman, M. J. Bernardinelli, P. H. et al. A Well-Characterized Survey for Centaurs in Pan-STARRS1 73 ad9a58
Ejeta, C. Gibb, E. DiSanti, M. A. et al. Infrared Compositional Measurements in Comet C/2017 K2 (Pan-STARRS) at Heliocentric Distances Beyond 2.3 au 102 ada154
Jewitt, D. Luu, J. Li, J. Demise of Kreutz Sungrazing Comet C/2024 S1 (ATLAS) 105 ada3c0
Comet Blanpain is held up as the textbook fading, not-yet-dormant comet. It is then a key point on the scale of comets, from new, long-period, fresh examples that may be making their very first pass through the inner Solar System, all the way to truly extinct comet nuclei. (Not that we’re sure a body is truly extinct, and not just dormant, by remote observation alone.)
Centaurs, by their very nature, are assumed ice-bearing; they simply never get close to the Sun (thanks to the orbital definition of “Centaur”) and never display much activity, like your stereotypical comet. But some do, just not that much. The more centaurs, the less we assume.
The study of comets really couldn’t have happened until the modern age. The volatiles released (yes, volatileS plural) have few if any spectral lines in the visible range. We then can’t really get a good read on what’s coming out of that nucleus. No, most of the spectral features are in the infrared or ultraviolet, which means comet studies didn’t take off until infrared and, to a lesser extent, ultraviolet astronomy could develop. And now here’s another example, observed.
If centaurs never get close to the Sun, the Kreutz family of comets gets too close. Many make one pass, and vanish- they get that close that few, if any, refractory mineral particles emerge from the other side of the Sun. It is even speculated that the sungrazers contain no traditional volatile molecules at all. Their perihelion passage is so close and so hot, rock itself escapes- we are seeing the less-refractory minerals form the coma and tail. C/2024 S1 is one such doomed Kreutz object.