Characterizing newly discovered distant comets

Comets are remnants of planet formation, spending most of their lifetime relatively unchanged in the outer Solar System. Dynamically new comets (DNCs) are comets with nearly parabolic orbits suggesting they are entering the inner Solar System for the first time. DNCs are valuable probes for connecting observed cometary properties to conditions in the pre-solar nebula and subsequent evolution, as they are considered to be mostly primordial with limited solar heating before discovery. However, the mechanisms behind cometary activity at large distances are not well understood. Surveys today (e.g., Pan-STARRS, ZTF) can discover comets at further distances from the Sun than ever before, allowing for more distant and longer baseline observations compared to DNC studies conducted in the past. We have begun monitoring newly discovered, distant long-period comets (LPCs). Since August 2020, our Las Cumbres Observatory (LCO) Outbursting Objects Key project has observed LPCs discovered inbound beyond 5 au, and since February 2021, we have also used the SOAR telescope to observe LPCs discovered inbound beyond 10 au. Both projects seek to monitor the brightness evolution, colors, and coma morphology of distant comets to better understand the behavior of comets at distances beyond which water sublimation is expected to be the driver of activity with a goal of being able to distinguish between new and returning objects independent of dynamical modeling. These projects are complementary; the 1-m telescopes of LCO observe the brighter objects at cadences of a few days, while the 4.1-m SOAR observes the fainter, more distant targets approximately monthly. By consistent monitoring at large distances, we will be able to better understand the processes driving distant cometary activity and make better predictions of brightness behavior of future discoveries. We will present our preliminary results and will particularly highlight our ongoing observations of C/2014 UN271 (Bernardinelli-Bernstein), which was discovered to be active beyond 20 au and appears to be among the largest known comet nuclei.

Cross-listed as presentation #301.05.