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

Abstract

We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD2 taken 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 ∼1 m s-1 speeds with a ∼1' jet pointing in the southwest direction. LD2 experienced a total dust mass loss of ∼108 kg at a loss rate of ∼6 kg s-1 with Afρ/cross section varying between ∼85 cm/125 km2 and ∼200 cm/310 km2 from 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/CO2 gas production of ≲1027 mol s-1/≲1026 mol 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-1 scaling from our estimated C2 production of ${Q}_{{C}_{2}}\\lesssim 7.5\\times {10}^{24}$ mol s-1 from 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 × 106 yr, having a dynamical half-life of 3.4 × 105 yr.