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Long Period Comets are Vehicles to the Past: The Systematic Analysis of 100+ Long Period Comets

Presentation #400.09 in the session Comets: Coma (Oral Presentation)

Published onOct 23, 2023
Long Period Comets are Vehicles to the Past: The Systematic Analysis of 100+ Long Period Comets

Long-period comets (LPCs) contain the most pristine volatiles, organics, and refractory materials, preserving the chemical characteristics of the early proto-planetary disk. However, they are the least studied objects in our solar system when it comes to their colors and activity. There are still fundamental questions remaining regarding LPC observations in comparison to theory: a) we observe fewer LPCs with lower orbital energies (less eccentric orbits) than expected. Jan Oort suggested that this is because a comet from the Oort cloud will lose extremely volatile material after it’s first passage through the inner solar system, which will cause the comet’s brightness to fade over time. However the details concerning the physical processes behind cometary fading are not widely agreed upon. b) Understanding LPC colors is crucial because color provides insights into LPC surface properties. Previous studies indicate that outgassing may influence colors, and Oort proposed a possible connection between comets’ surface colors and their dynamical histories. To address Oort’s hypotheses, we need to model LPC activity and quantify the volatile production rate (sublimation of ice) as a function of distance from the sun. For this purpose, we conducted a large survey of newly discovered LPCs and their activity. Our 3-year program focused on a sample of over 100 newly discovered LPCs with diverse orbits with perihelia between 0.9 and 8 au. Our program involved coordinated multi-epoch photometric observations from CFHT. For one third of our targets, we obtained griZY photometric colors or spectra from the Gemini N/S or Keck telescopes. Our work represents the first comprehensive study of cometary activity for faint LPCs and utilizes a dataset that is ten times larger than previous studies. For our analysis we employed a dust model for each comet to determine their dust grain size distributions, production rates, and emission velocities of ejected grains in the dust tail. We utilized an improved ice-outgassing model to constrain nucleus size and identify the sublimating ice species and fractional active areas for each target. For individual comets that required a delayed onset of activity from CO or CO2 we employed a 1-D thermal model to estimate the depth of ice for our targets. Although our analysis is still ongoing, we will report the results for a sub-sample of our targets as part of this study.

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