The Classical and Large-a Distant Solar System Survey: the Importance of Outer Resonances

NASA Solar System Observations Program

Subaward to PSI from Smithsonian Astrophysical Observatory

PI: Rosemary Pike

Start Date: 09/01/2023
Project #: 1947
End Date: 08/31/2026
Award #: SV1-31013
Project Description

The outer solar system is populated with large numbers of small, icy bodies, but the extent of these trans Neptunian objects (TNOs) and the relative populations of the different TNO sub groups requires further study. The dynamically “cold” classical TNOs have distinct physical properties and are observed between ~42 48 au; they are likely an in situ remnant of a primordial planetesimal disk whose exact original radial extent is still an open question. The dynamically excited “hot” TNOs likely formed inside ~30 au and were scattered into the scattering, resonant, and detached populations, with predicted distributions that depend sensitively on giant planet migration models. Using the current TNO orbital distribution to constrain the formation and evolution of the outer solar system requires a large sample of TNOs with known discovery biases.

We will contribute to the Classical and Large a Distant Solar System Survey (CLASSY), which will discover 500 600 TNOs from 2022 2024 with well characterized discovery biases. CLASSY is a deep survey (limiting r band magnitude of ~26.5), increasing the sensitivity for large objects (hundreds of km) to >700 au and for typical sized objects (100 150 km) to 40 55 au. CLASSY will definitively characterize the nature of the classical Kuiper belt’s outer edge near 47 au and provide new, strong constraints on low eccentricity populations of distant detached and resonant TNOs beyond this edge. CLASSY’s sensitivity is particularly valuable for constraining the high pericenter distant detached and resonant TNOs. The on sky distribution of the “extreme” detached TNOs has been interpreted as evidence for an additional planet, but the distant resonant and detached TNOs could also be sculpted by past rogue planets or stellar flybys; a larger observational sample with known discovery biases is required to test proposed explanations for their origins. We will perform observational... will perform observational follow up and dynamical characterization of CLASSY’s distant detections to enable these tests. We will also constrain the population of Neptune’s 5:2 resonance at ~55 au, which has a surprisingly large population. Most observed 5:2 members have large eccentricities, but this is consistent with prior surveys’ strong biases against low eccentricity members. Simulations of giant planet migration typically capture large eccentricity objects into the 5:2 via outward scattering from the hot TNO population; however, if the initial cold planetesimal disk extended beyond the current edge, sweeping capture may have populated the 5:2 with lower eccentricity TNOs. Such capture is only hinted at in the current data, but CLASSY will be much more sensitive to this potential 5:2 population. We will use CLASSY to constrain the low eccentricity 5:2 population and test existing migration scenarios.

PI: Rosemary Pike (Smithsonian Astrophysical Observatory)

Co Is: Kathryn Volk (PSI), Ruth Murray Clay (UC Santa Cruz)

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