Free Astronomy Magazine May-June 2015

SMALL BODIES T he comet pho- tographed by Rosetta’s NavCam on 28 March 2015, from 19.9 km away. [ESA/Ro- setta/NAVCAM – CC BY-SA IGO 3.0] S ome interest-i- ng surface structures of the comet: the A and B arrows indicate some bright and bluish patches, probably com- posed of ice; the C, bright boulders of uncertain nature; and D, soft ground. [ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/ IAA/SSO/INTA/ UPM/DASP/IDA] information from other instruments) has allowed to correctly interpret its several contacts with the ground and its orienta- tion. What for most scientists and techni- cians had been an imperfect landing, turned out to be a happy mishap for the Rosetta Lander Magnetometer and Plasma Monitor (abbreviated in ROMAP) team, since the unexpected Philae’s tumbles have allowed to collect precise measurements of the magnetic field around it, both at the four points of contact with the surface and over a wide range of heights above the sur- face (thanks to the bounces). By including also the data collected during the long ini- tial descent (about 20 km in 7 hours), the ROMAP team found that the strength of the magnetic field detected around 67P/ Churyumov-Gerasimenko is neither related to the height or the surface location of Phi- lae. If the comet’s nucleus was equipped with its own magnetic field (resulting from the sum of the magnetism contributed by the magnetite molecules), during approach to the surface, ROMAP would have record- ed a rising force, while in moving away it should have recorded a decrease thereof. Additionally, from a region of the cometary surface to another it could have been ex- pected to detect small local variations in the magnetic field, related to the confor- mation of the nucleus and to its surface