First Detection of a Diamagnetic Cavity at 67P/Churyumov-Gerasimenko
Wednesday, 16 December 2015: 14:10
3014 (Moscone West)
The magnetometer onboard the Rosetta spacecraft (RPC-MAG) has been measuring the evolution of the plasma interaction region at comet 67P/Churyumov-Gerasimenko since its arrival in August 2014. After a weak phase with low gas-production rates, the activity increased and has resulted in the build up of the magnetic field strength. At the end of July 2015, the average magnetic field strength was ~40 nT with turbulence in the order of up to ~40nT. In this regime, RPC-MAG has detected short intervals (2-25 minutes) where the magnetic field strength drops below 5nT and all wave activity ceases. These signatures are interpreted as the presence of a diamagnetic cavity. This type of field-free region has only been observed once before at comet 1P/Halley during a fast flyby, but the Rosetta mission now affords the opportunity to study several such intervals where the cavity region is expanding due to higher gas production rates and thus measurable by RPC-MAG at a radial distance of 200 km from the comet. The observations are well supported by theoretical predictions and numerical simulations.