Contemporaneous Multi-Wavelength and Precovery Observations of Active Centaur P/2019 LD2 (ATLAS

TL;DR

This study presents multi-wavelength observations of Centaur P/2019 LD2, providing insights into its activity, composition, and transition towards becoming a Jupiter Family Comet, which enhances understanding of small body evolution in the Solar System.

Contribution

First contemporaneous multi-wavelength observational campaign of LD2, revealing its activity, composition, and potential transition to a Jupiter Family Comet.

Findings

LD2's nucleus radius <= 1.2 km with no large outbursts

Dust production rate ~10-20 kg/s and outflow velocity 0.6-3.3 m/s

Detection of water ice at 1-10% level depending on grain size

Abstract

Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) (Sarid et al. 2019) provides the first opportunity to observe the migration of a Solar System small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now (Kareta et al., 2020; Hsieh et al. 2020). The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multi-wavelength observations of LD2 from 2020 July 2-4: Gemini-North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO SMT millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleu's effective radius to <=1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has g'-r'=0.70+/-0.07, r'-i'=0.26+/-0.07, a dust production rate of ~10-20 kg/s, and an outflow velocity between v~0.6-3.3 m/s. We did not detect CO towards LD2 on 2020 July 2-3, with a 3-sigma upper limit of Q(CO) < 4.4 * 10^27 mol/s (<200 kg/s). Near-infrared spectra show evidence for water ice at the 1-10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long baseline monitoring effort.