Modern sky surveys are now discovering comets at distances beyond 5 to 10 au from the Sun, a distance that is expected to increase with the upcoming Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). However, the mechanisms driving comet activity at such distances remain poorly understood, as temperatures are too low for water ice sublimation, the usual driver closer to the Sun. Activity at these distances is likely driven by more volatile ices such as CO and CO2, or by phase transitions in amorphous water ice, but the relative importance of these processes remains uncertain. As part of our Las Cumbres Observatory (LCO) Outbursting Objects Key (LOOK) project, we have been monitoring ~50 long-period comets discovered inbound beyond 5 au from the Sun using LCO’s global network of 1-m telescopes since 2020. In this talk, I will present brightening trends of distant long-period comets and discuss empirical models for comet activity that better capture their behavior across large heliocentric distance ranges. I’ll highlight how these findings improve our understanding of the mechanisms driving distant comet activity, and discuss the implications for LSST predictions and target selection for the ESA Comet Interceptor mission.<\/p>\n
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