Sorry, but I forgot the Astronomical Journal for September. In Volume 168, Number 3, 2024 September 2, there was one paper to mention, but what a mention:
Yu, L-L. Probe the Regolith Characteristics of Asteroids from 9 yr Infrared Observations of WISE/NEO… a 120 ad65d0
Using data from the WISE spacecraft (extended into its NEOWISE mission), Yu studies object (656) Beagle, a Main Belt object. I say “object,” not “asteroid,” for a reason. The Themis family of Main-Belters includes multiple Main Belt Comets- objects which have faint comas and tails. They straddle the line between literal, stereotypical asteroids and comets. To be technical, we simply call them “Small Solar System Bodies” after the 2006 IAU meeting recognized Main Belt Comets and other boundary cases. Among Small Bodies, a “family” is a group of such objects that all have similar orbits; we presume (sometimes hastily) that they all spread outward from a collision on some parent body. Either the parent is the largest object within the family, or sometimes the parent object was destroyed, and the family is the pieces left. The largest Themis family object is Themis itself; after Main Belt Comets were found in the family, it was seen that Themis has spectra of some ice on its surface. Cool, eh?
The object (656) Beagle, based on its orbit, appears to be in the Themis family, unless we’re too hasty. A possibility is that Beagle is just there coincidentally- an “interloper” in the Themises. Another option is that Beagle- and lesser asteroids near Beagle- forms its own subfamily.
Is Beagle, like Themis and some Themis-family objects, an icy object, in some asteroid-comet grey area? Yu wants to know. In longer wavelengths (infrared), we can gather more data than conventional (visible) telescopes. We can tell something about chemical/mineral makeup if we have certain wavelengths, but the WISE craft ran out of coolant pretty quickly for this. Simply telling if the object is warmer or cooler already tells us about the surface and near-surface; an exterior of loose regolith (like a gravelly road) will heat and cool differently than a ‘solid’ surface (like either smooth pavement, or maybe sand so fine it packs tightly). This “thermophysical study” requires some assumptions but is a powerful technique at small bodies. At minimum, it’s one more piece of a puzzle, the other pieces sometimes being assumptions, sometimes being solved from what had been prior assumptions.
I already stated that NASA’s Infrared Telescope Facility (IRTF) was a big player in follow-up. WISE, a mission in low Earth orbit, can’t have its coolant refilled, but did admirable duty while it could. (In its extended mission, simply radiating away its heat to deep space did a fair job of cooling WISE.) Now, WISE is decaying in its orbit; the last little remnants of Earth’s atmosphere at that altitude cause drag, and the spacecraft slowly falls. WISE has already shut down operations; pretty soon now, it will reenter completely, and burn up. We can look back proudly at the mission dataset (back since 2009!), and all it did for the Small Body community. Thanks for all the bits, WISE!