Contemporaneous Multiwavelength and Precovery Observations of the Active Centaur P/2019 LD2 (ATLAS)

The Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) 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. 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 multiwavelength observations of LD2 from 2020 July 2-4: Gemini North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO Submillimeter Telescope millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleus's effective radius to ≤1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has $g^{\prime} -r^{\prime} =0.70\pm 0.07$ , $r^{\prime} -i^{\prime} =0.26\pm 0.07$ , a dust-production rate of ∼10-20 kg s^-1, and an outflow velocity between v ∼ 0.6-3.3 m s^-1. We did not detect CO toward LD2 on 2020 July 2-3, with a 3σ upper limit of Q(CO) < 4.4 × 10²⁷ mol s^-1 (⪅ 200 kg s^-1). 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.