The Orbit and Size of the Active Jupiter Co-Orbital P/2023 V6 (PANSTARRS)

P/2023 V6 (PANSTARRS) is the second-known active Jupiter co-orbital comet after the well-studied P/2019 LD2 (ATLAS). These two objects, along with other populations like the Gateway Centaurs and those comets temporarily captured by Jupiter, are some of the best analogues for the objects which impact Jupiter and thus their physical properties are of interdisciplinary relevance. Starting in 2023, we began a campaign of telescopic characterization of V6 that culminated in observations with the Hubble Space Telescope in December 2024. While V6 was always dimmer than LD2, even at its slightly warmer perihelion, initial characterization efforts reported in Kareta et al. (2024) suggested that this was most likely due to V6 being physically larger but with a significantly lower active fraction – in essence, it was more ‘evolved’ than LD2. The comet appeared to be experiencing stable (e.g., not outburst driven) activity around peak brightness much like LD2 has been four years prior.

In this talk, we will present our analyses of later ground-based and HST observations which show that the opposite might be true; V6 is very small and was just as active as LD2 was at a similar distance, if not moreso. The HST images are consistent with an object with a diameter of just about a few hundred meters assuming a typical cometary albedo and phase curve, almost certainly the smallest cometary nucleus detected at such a distance. A precipitous decline in brightness and mass loss rates in V6 just months after its perihelion passage, however, is quite unlike its more active cousin and cannot be explained by the object crossing any major ice lines or as an observational bias. We could not detect V6 with any confidence in two nights of ground-based imaging late in 2024 and early 2025, and the HST images don’t appear to show any dust around the point-source-like object at all. This indicates that the objects do still have significant differences in the physical states of their nuclei and in the talk we will present several hypotheses that might be tested through studies of other near-Jupiter comets in the Rubin era. We will also comment on how advances in understanding the properties of these comets might help interpret the cratering record of the Galilean satellites and thus in assessing how often material from impactors gets through the ice to the oceans beneath.