Interstellar Comets from Post-main-sequence Systems as Tracers of Extrasolar Oort Clouds

Abstract

Interstellar small bodies are unique probes into the histories of exoplanetary systems. One hypothesized class of interlopers are “Jurads,” exocomets released into the Milky Way during the post-main-sequence as the thermally pulsing asymptotic giant branch (AGB) host stars lose mass. In this study, we assess the prospects for the Legacy Survey of Space and Time (LSST) to detect a Jurad and examine whether such an interloper would be observationally distinguishable from exocomets ejected during the (pre-)main-sequence. Using analytic and numerical methods, we estimate the fraction of exo–Oort Cloud objects that are released from 1–8 M ⊙ stars during post-main-sequence evolution. We quantify the extent to which small bodies are altered by the increased luminosity and stellar outflows during the AGB, finding that some Jurads may lack hypervolatiles and that stellar winds could deposit dust that covers the entire exocomet surface. Next, we construct models of the interstellar small body reservoir for various size–frequency distributions and examine the LSST’s ability to detect members of those hypothesized populations. Combining these analyses, we highlight the joint constraints that the LSST will place on power-law size–frequency distribution slopes, characteristic sizes, and the total mass sequestered in the minor planets of exo–Oort Clouds. Even with the LSST’s increased search volume compared to contemporary surveys, we find that detecting a Jurad is unlikely but not infeasible given the current understanding of (exo)planet formation.

The Galactic Interstellar Object Population: A Framework for Prediction and Inference

“…Since the majority of ISOs are expected to be ejected by dynamical processes within several hundred megayears of a star's formation (Pfalzner & Bannister 2019;Fitzsimmons et al 2023), we assume that the birth of a star and release of its ISOs are contemporaneous, and omit accounting for any delay. A fraction of a planetary system's bound planetesimals will become unbound later in a system's life, whether from its Oort cloud's continuous interaction with the Galactic environment, or in post-main-sequence escape (Veras et al 2011(Veras et al , 2014Levine et al 2023); for simplicity we omit this smaller population here. As Oort Cloud comets, which also occupy an interstellar environment (Kaib & Volk 2022), do not exhibit substantive erosion after 4.5 Gyr (Stern & Shull 1988), we continue with the expectation that ISO erosional processes are broadly similar to those of solar system comets (e.g., Guilbert-Lepoutre et al 2015).…”