16878

The recently discovered large long-period comet C-2014 UN271 has been observed to be active as far away as virgul24 au. The cause of its activity is unclear because this is beyond the heliocentric distance at which many common cometary activity-driving volatiles significantly begin to sublimate. We comma therefore comma propose to use six orbits of HST time over three visits to make high-resolution color maps of the coma of C-2014 UN271 determining its coma-centric color slope testing the presence of icy grains in its coma and to constrain the ejection velocity of the dust. Revealing the presence or lack of ice grains as the comet is inbound into the inner Solar System would provide direct observational constraints on whether its activity mechanism is driven by hypervolatiles. Determining the ejection velocity of the dust will provide independent constraints on the activity mechanism. In addition to determining the color map of C-2014 UN271 comma our observations will have legacy value for future interpretations of one of the few known large long-period comets comma volatile content and evolution as it approaches the Solar System.