I am a funded U.S. investigator working on the Rosetta mission, a European Space Agency small body mission. I have been focusing in particular on Rosetta's encounter with asteroid (21) Lutetia and comet 67P/Churyumov Gerasimenko.
New constraints on the density, composition, and morphology of 21 Lutetia from Rosetta indicate that Lutetia's high bulk density exceeds that of most known chondritic meteorite groups (Sierks et al. 2011; Paetzold et al. 2011), yet its surface properties resemble those of some chondrite groups (Weiss et al. 2012). This indicates that Lutetia likely experienced early compaction processes like metamorphic sintering. It may have also partially differentiated, forming a metallic core overlain by a primitive chondritic crust.
In 2014, the ROMAP magnetotometer aboard the Philae lander acquired magnetic field measurements across the surface of comet Churyumov-Gerasimenko. ROMAP found no evidence for an intrinsic field at the comet's surface (less than 0.9 nT). This suggest that the nebular magnetic field was below 3 μT at 15-45 AU from the young Sun (Biersteker et al., submitted). This constraint is consistent with theories of magnetically-driven evolution of protoplanetary disks.