In November 1’s issue (vol. 993 #1) of Astrophysical Journal Letters:
Farnocchia, D. Vokrouhlicky, D. Santana-Ros, T. et al. Radiation Forces and Trajectory of Hayabusa2# Target 1998 KY26 L9 ae10b8
Salazar Manzano, L. E. Lin, H-W. Taylor, A. G. et al. Onset of CN Emission in 3I/ATLAS: Evidence for Strong Carbon-chain Depletion L23 ae1232
Salazar Manzano et al. was covered here back when it was a preprint… now it’s a ‘print’.
Farnocchia et al., on the other hand, is timely and forward-looking. Hayabusa2, now on an extended mission (“2#”), will orbit and contact asteroid 1998 KY26. This asteroid has already been described (twice) as a “dark comet”- a body which displays no coma or tail (“activity”) in telescopes, and is thus officially listed as an asteroid. And yet, the body shows “nongravitational acceleration”- deviation from a simple orbit, due to (we presume) jetting, like a comet. If 1998 KY26 is deviating- ever so slightly- from its prior orbit, well, that’s something the Haya2 team would need to know to target it, eh? And that’s before the science team formulates their plan of study.
Another (somewhat related) issue is the very small size of the asteroid (or “asteroid”). As bodies get smaller and smaller, their area decreases by the square of the radius. However, their mass decreases with volume, which decreases by the cube of the radius. In other words, mass becomes less dominant, area becomes more dominant as bodies shrink. We call this the “square-cubed rule”. Since 1998 KY26 is the smallest asteroid ever targeted by a mission- and even smaller than anticipated years ago when chosen as a target- new issues come into play.
And that’s the Astrophysical in Astrophysical Journal- with less mass than anticipated, and area more dominant, we must account for radiation pressure. Literally, sunlight itself exerts a (tiny) force on areas placed in its illumination. This was negligible, even ignored, for larger asteroids… not now.