Small Cold Classical TNOs as Witnesses of Outer Nebular Chemistry
Session 1.08 Spectroscopy
Monday 06-24 | 12:00 - 12:20

We report on our JWST NIRSpec program collecting infrared spectra (1–5 μm) of a sample of small Cold Classical TNOs. New Horizons' 2019 encounter with Arrokoth had revealed its surface to be rich in organics such as methanol ice, but no obvious water ice absorption features were seen. Methanol ice has been found in dense cloud cores prior to star formation, where it forms through hydrogen addition on CO ice. It has been shown through laboratory experiments to be an important step towards more complex organics. We are thus searching among the Cold Classical TNOs that are thought to still be in the locations where they formed for potential compositional trends with heliocentric distance or with size that could shed light on a hypothesized region of distinct nebular chemistry beyond the CO snow line. Our sample is divided into two slices. The first slice matches Arrokoth's 44 AU heliocentric distance, while varying the objects' sizes over the absolute magnitude (HV) range from 9 to 7. For Arrokoth's albedo, these correspond to spherical diameters from 44 to 110 km. Larger Cold Classicals have been observed through the Discovering the Surface Compositions of TNOs (DiSCo-TNOs) program, broadening the size range available for comparison, although objects as small as Arrokoth (HV=11, spherical diameter 18 km) would have been prohibitively costly to include. The second slice consists of objects sharing the same absolute magnitude HV=8 (corresponding to 70 km diameter for Arrokoth's albedo), but orbiting at heliocentric distances from 42.6 to 46.6 AU.

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