The Volatile Content of Oort Cloud Comet C/2014 UN271

Oort Cloud comets are remnants of the original planetesimals that were ejected from the planetary region in the late stages of planetary formation. The Oort Cloud comet C/2014 UN271, hereafter UN271, is ~140 km in diameter, large enough that it could be an intact example of a planetesimal that formed in the protoplanetary disk before being ejected into the Oort Cloud. UN271 has been at >20 au from the Sun. Given its large heliocentric distance, it is likely that its activity is driven by hypervolatiles such as CO or CO2 and not H2O. UN271 is on its first inbound trip to the Solar System's planetary region providing the rare opportunity to study the volatile contents of one of the original planetesimals in a pristine state. We propose NIRSpec IFU observations of UN271 covering the spectral range where vibrational bands of gas-phase hypervolatiles (such as CO/CO2) as well as solid-phase water-ice grains can be detected. Our observations will provide constraints on the comet's CO and CO2 production rates, the activity driving mechanism, and the presence and nature of water-ice grains in its coma. We request observations now so the comet's behavior can be established before rapid changes occur in the comet's activity due to the increasing thermal pulse from the Sun. The detection of volatiles and constraints on the activity of the largest known Oort Cloud comet and one of the original planetesimals will be tremendously exciting and useful for placing constraints on the volatile contents and timing of the formation of the original planetesimals. These observations will be combined with observations from HST to maximize the science of both datasets spanning the visible and NIR.