Vehicles to the Past: Characterizing the Activity of Long Period Comets
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2024
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Long-period comets (LPCs) contain some of the solar system's most pristine volatiles, organics, and refractory materials, preserving chemical markers from the early proto-planetary disk. Despite their importance, LPCs are among the least studied in terms of activity. Observations reveal fewer LPCs with lower orbital energies (less eccentric orbits) than expected. Jan Oort suggested this scarcity results from LPCs losing volatile material after their initial passage through the inner solar system, causing their brightness to diminish over time. However, the precise physical processes behind cometary fading are still debated. To investigate these processes, we systematically modeled LPC activity and quantified volatile production rates as a function of solar distance, focusing on nearly 100 newly discovered LPCs with perihelia between 0.9 and 10 au. Our program combined multi-epoch photometric observations from CFHT and Gemini, supported by amateur and all-sky survey data. We use our new tool – the Volatile Activity Monitoring and Prediction (VAMP) python code - which is an augmented and improved version of an existing sublimation model - to measure nucleus sizes, identify sublimating ices, and determine active surface areas. For comets with delayed CO2 activity, we used a 1-D thermal model to estimate ice depths. Our findings indicate that CO2 sublimation plays a key role in outbursts and delayed activity onset, and we propose that periodic thermal processing of the nucleus, such as dust-mantle accumulation, and stochastic processes, such as activity caused by recondensing volatiles or avalanches that eventually lead to nucleus fracture may explain the scarcity of low-energy LPCs.
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Astronomy, Comet, Solar System
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747 pages
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