We present Infrared Telescope Facility/SpeX and NEOWISE observations of the dynamically new comet C/2013 US10 (Catalina), hereafter US10, from 5.8 au inbound, to near perihelion at 1.3 au, and back to 5.0 au outbound. We detect water ice in the coma of US10, assess and monitor the physical properties of the ice as insolation varies with heliocentric distance, and investigate the relationship between water ice and CO2. This set of measurements is unique in orbital coverage and can be used to infer both the physical evolution of the ice, and, potentially, the nucleus composition. We report (1) nearly identical near-infrared spectroscopic measurements of the coma at -5.8 au, -5.0 au, +3.9 au (where <0 au indicates pre-perihelion epochs), all presenting evidence of water-ice grains, (2) a dust-dominated coma at 1.3 and 2.3 au and, (3) an increasing CO2/Afρ ratio from -4.9 to 1.8 au. We propose that sublimation of the hyper-volatile CO2 is responsible for dragging water-ice grains into the coma throughout the orbit. Once in the coma, the observability of the water-ice grains is controlled by the ice grain sublimation lifetime, which seems to require some small dust contaminant (i.e., non-pure ice grains). At |Rh| ≥ 3.9, the ice grains are long-lived and may be unchanged since leaving the comet nucleus. We find that the nucleus of comet US10 is made of, among other components, ∼1 μm water-ice grains containing up to 1% refractory materials.
Bibliographical noteFunding Information:
Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration.
This work was supported by NASA’s SSO grant NNX15AD99G. S.P. thanks the NASA grant NNX16AC83G for partial funding that supported her work. M.S.P.K. acknowledges funding from NASA PMDAP grant NNX 13AQ10G. C.E.W. appreciates support from NASA EW grant NNH15ZDA001N.
The authors gratefully thank the staff of IRTF for their assistance with this project. This publication also makes use of data products from NEOWISE, which is a project of JPL/ Caltech, funded by the Planetary Science Division of NASA. We thank the anonymous referee for valuable suggestions. This research made use of ephemerides from JPL Horizons (Giorgini et al. 1996). Facilities: IRTF (SpeX), WISE. Software: Astropy (Astropy Collaboration et al. 2013).
- comets: individual (C/2013 US10 (Catalina))
- radiative transfer
- techniques: spectroscopic Supporting material: data behind figures