NICER observation list: Target ID 555503

We request 94 ksec of NICER observing time to study the solar-wind interaction of comet C/2017 K2 at 4 distinct epochs along its orbit. C/2017 K2 is a long-period comet on a highly eccentric orbit that will bring it to its first perihelion in December 2022. K2 is a particularly notable comet because it showed activity at a record-setting distance from the Sun on approach, suggesting a peculiar chemical composition, likely very rich in CO ice. We will test theoretical predictions of the effect of comet chemistry on charge-exchange emission spectra, study the spectral evolution of K2 as its activity evolves and is exposed to different solar wind conditions, and investigate the source of poorly understood cometary 1 -2 keV emission features.