Free Astronomy Magazine May-June 2015

T he video above shows the Philae mission on 67P/Churyu- mov-Gerasimen- ko as originally scheduled. [ESA/ATG media- lab] Right, the sizes of the main parts of the comet. [Science] I n this image of 67P/Churyumov-Gerasi- menko, the red oval line circumscribes the area inside which Philae is hidden in a shaded location. [ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA] of a cascade-like aggregation which would first lead to the formation of planetesimals and then of comets, asteroids, moons and planets. But astronomers did not know up to what bodies' size the magnetic fields could play a key role in the progression of accretion before the gravity action becomes dominant. The Rosetta mission provided us the oppor- tunity to shed light on those mechanisms and ascertain whether, as some theories suggest, the aggregation of magnetic and non-magnetic material can produce a body of significant size characterized by magne- tism. A cometary nucleus is a very suitable subject for this purpose, since composed of primordial materials that have not under- gone significant changes. Before the Roset- ta mission there had never been an oppor- tunity to discover and possibly measure a cometary magnetic field, since the few pre- vious encounters between probes and com- ets had occurred at speeds that were too fast and for periods too short for that kind of research.