Multispectral comparison of water ice deposits observed on cometary nuclei

Cometary missions Deep Impact, EPOXI and Rosetta investigated the nuclei of comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko respectively. Each of these three missions was equipped with multispectral cameras, allowing imaging at various wavelengths from NUV to NIR. In this spectral range, water ice-rich features display bluer spectral slopes than the average surface and some have very flat spectra. Features enriched in water ice are bright in the monochromatic images and are blue in the RGB color composites generated by using images taken in NUV, visible and NIR wavelentghs. Using these properties, water ice-rich features were detected on the nuclei of comets 9P [1], 103P [2] and 67P [3] via multispectral imaging cameras. Moreover, there were visual detections of jets and outbursts associated to some of these water ice-rich features when the right observing conditions were fulfilled [4, 5].We analyzed multispectral properties of different types of water ice-rich features [3] observed via OSIRIS NAC on comet 67P in the wavelength range of 260 nm to 1000 nm and then compared with those observed on comets 9P and 103P. Our multispectral analysis shows that the water ice deposits observed on comet 9P are very similar to the large bright blue clusters observed on comet 67P, while the large water ice deposit observed on comet 103P is similar to the large isolated water ice-rich features observed on comet 67P. The ice-rich deposits on comet 103P are the bluest of any comet, which indicates that the deposits on 103P contain more water ice than the ones observed on comets 9P and 67P [6].[1] Sunshine et al 2006, Science[2] Sunshine et al 2011, LPSC[3] Pommerol et al 2015, A&A[4] Oklay et al 2016, A&A[5] Vincent et al 2016, A&A[6] Oklay et al 2016, submitted