Unexpected and significant findings in comet 67P/Churyumov-Gerasimenko: an interdisciplinary view

ESA's Rosetta Mission has followed Comet 67P/Churyumov-Gerasimenko from 3.6 au inbound to 3.6 au outbound. Many results are largely unexpected, as compared to previous models based on in situ and ground-based observations of Jupiter-family comets. The main topics discussed in this review are (1) the importance of the large concavities characterizing the 67P nucleus, that, (2) coupled to the nucleus obliquity, make seasons an unexpectedly important source of many phenomena observed in this and probably in most comets; (3) the mostly uniform distribution of ices over the nucleus surface; (4) the high dust-to-water mass ratio, which implies that much of the nucleus mass is in the form of minerals partly coming from the inner proto-solar nebula, thus making 67P very porous and less hydrated than primitive CI chondrites. 67P nucleus may have never experienced any collision at speeds larger than 1 m s^-1.