Referencing Taylor et al. 2024:
Aug 7 Jonathan O’Callaghan The mysterious ‘dark comets’ prowling our Solar System
www.bbc.com/future/article/20250807-a-japanese-spacecraft-is-racing-toward-a-mysterious-dark-comet-to-discover-the-secrets-it-holds
The BBC- usually pretty good on technical topics- has a nice writeup of our current state in “dark comets”- asteroids that show nongravitational acceleration. Comets get nongravitational acceleration when their jetting is less than symmetric. So, an asteroid that shows NGA is a… what, exactly? A small Solar System body, for one. The term SSSB was endorsed in 2006 by the IAU, when the line between “comet” and “asteroid” was visibly shattered by Main-Belt comets.
And now the Hayabusa2 probe’s extended mission (Hayabusa2#, that’s “hayabusa two sharp”) will- barring an incident- orbit 1998 KY26. That asteroid has been seen to display NGA. In several years (it’s a roundabout trip), we’ll see our first dark comet up close.