  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.
