Wow, what an Astronomy Journal (AJ) for Dec (vol. 170 #6):
Willacy, K. Majumdar, L. Bonev, B. et al. The Interstellar Heritage of Comets Art 312 ae0cae
Hou, X. Tan, P. Liu, X. et al. Influence of Planetary Flyby Events on Binary Asteroid’s Impact Risk Art 347 ae1575
Stetzler, S. Jurić, M. Bernardinelli, P. H. et al. An Efficient Shift-and-stack Algorithm Applied to Detection Catalogs Art 352 ae0e1a
Fuentes-Muñoz, O. Farnocchia, D. Giorgini, J. D. et al. Asteroid Mass Estimation by Mutual Perturbations During Close Encounters After Gaia Focused Product Release Art 353 ae0cc9
Comets form in the outer Solar System, and stayed there until something perturbed them inward. Forming in the outer Solar System includes forming with, and then taking infall from, the interstellar medium of the nearby Milky Way. Just how much ‘comet stuff’ is nonsolar? Willacy et al. ask.
And now planetary defense gets into the weeds. A nontrivial number of asteroids (including NEOs) are binary or higher multiples. When a multiple system passes close to a planet, the gravity (tides, specifically) can pull apart the components, even separating them completely. The two (or more) bodies then continue on disturbed new paths. Since the fraction of multiple NEOs may be as high as one-sixth, pondering this splitting and disturbing process may be the difference between impacting or not.
Previously reported (and reported again): Stetzler et al. give their asteroid search algorithm, except here accepted by a rigorous, prestigious journal. Without even using a telescope, computers can search archival images, to match up asteroids (previously unrecognized) over time. Good luck!
And speaking of multiple asteroid systems: A quirk of a multi-system is that flyby and pulling process. By gauging how badly a binary (or higher) system gets distorted, one can deduce the gravity (and therefore mass) in the system. A massive asteroid should hold its satellite tighter against disturbances. Using the sky search archives of the Gaia mission, Fuentes-Muñoz et al. try to deduce those masses. Gaia: truly, a mission that keeps on giving and giving!