Catching up on Icarus– the 15 January 2025 issue (vol. 426) is a mid-month ‘issue’:
Caldiero, A. Le Maistre, S. Expected constraints on Phobos interior from the MMX gravity and rotation observations Article 116343 .2024.116343
Hoffmann, T. Micheli, M. Cano, J-L. et al. Debiasing astro-photometric observations with corrections using statistics (DePhOCUS) Article 116366 .2024.116366
Again, MMX is built and ready to fly. Trying to get every last bit of information out of the mission is one of the stakes. There will likely be no MMX 2 if anything falls short; there was no Phobos-Grunt 2, remember. Per previous small-body probes, the gravity of the target (and thus, its mass) will be an investigation attempted. The gravity of Phobos will have effects on MMX we can measure. Aside from that, Phobos should librate (‘bob’) from minor forces on it. Measuring these slight motions will also tell us of its makeup. Enough digits, and we get mass distribution.
Once we detect a new small body, we attempt to characterize it. First is a precise orbit, but that requires only a dot of light on the sky. It’s still not a ‘world’ or ‘place’ yet. Second or third comes a lightcurve- how bright is the target, and does brightness change, how? Is the target rotating, and does that rotation reveal bright and dark spots, an oblong shape, or something else- maybe a satellite? Or activity- is the ‘asteroid’ somehow having mass loss? All these questions tie to photometry- brightness measurement- and all measurements are abstractions, not absolutes. Approaching absolute brightness needs calibration, and we can’t even standardize on a single filter set (for some good reasons). Hoffman et al. try to get photometry into a more-exact science.