Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS), Using Hubble, Spitzer, ZTF, Keck, Apache Point Observatory, and GROWTH Visible and Infrared Imaging and Spectroscopy

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD₂taken with Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3), Spitzer Space Telescope/Infrared Array Camera (Spitzer/IRAC), and the GROWTH telescope network, visible spectroscopy from Keck/Low-Resolution Imaging Spectrometer (LRIS), and archival Zwicky Transient Facility observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD2 has a radius between 0.2 and 1.8 km assuming a 0.08 albedo and a coma dominated by ~100 μm-scale dust ejected at ~1m s^-1speeds with a ~1' jet pointing in the southwest direction. LD₂experienced a total dust mass loss of ~108 kg at a loss rate of ~6 kg s^-1with Afρ/cross section varying between ~85 cm/125 km²and ~200 cm/310 km²from 2019 April 9 to 2019 November 8. If the increase in Afρ/cross section remained constant, it implies LD2's activity began ~2018 November when within 4.8 au of the Sun, implying the onset of H2O sublimation. We measure CO/CO₂gas production of ≤10²⁷mol s^-1/≤10²⁶mol s-1 from our 4.5 μm Spitzer observations; g-r = 0.59 ± 0.03, r-i = 0.18 ± 0.05, and i-z = 0.01 ± 0.07 from GROWTH observations; and H2O gas production of ≤80 kg s^-1scaling from our estimated C₂production of Q_C2×7.5 × 10²⁴mol s^-1from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD2 is similar to Jupiter-family comets having close encounters with Jupiter within ~0.5 Hill radius in the last ~3 y and within 0.8 Hill radius in ~9 y. Additionally, 78.8% of our orbital clones are ejected from the solar system within 1 × 10⁶yr, having a dynamical half-life of 3.4 × 10⁵yr.