Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS)

<p>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 ∼1m 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<sup>−1</sup> with Afρ/ cross-section varying between ∼85 cm/125 km<sup>2</sup> and ∼200 cm/310 km<sup>2</sup> from 2019 April 9 to 2019 November 8. If the increase in Afρ/cross section remained constant, it implies LD2ʼs activity began ∼2018 November when within 4.8 au of the Sun, implying the onset of H2O sublimation. We measure CO/CO<sub>2</sub> gas production of <10<sup>27</sup> mol s<sup>−1</sup>/<10<sup>26</sup> mol s<sup>−1</sup> 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<sup>−1</sup> scaling from our estimated C<sub>2</sub> production of Q<sub>C2</sub> < 7.5 x 10<sup>24</sup> mol s<sup>−1</sup> 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 10<sup>6</sup> yr, having a dynamical half-life of 3.4 × 10<sup>5</sup> yr.</p>