Plasma waves near the diamagnetic cavity of comet 67P

Tid: Ti 2019-12-17 kl 13.15

Föreläsare: Elias Odelstad

Plats: Ivar Herlitz (Teknikringen 33, ground floor)

The European Space Agency's Rosetta spacecraft, which accompanied the comet 67P/Churyumov-Gerasimenko in its orbit around the sun between August 2014 and September 2016, provided the instruments in the Rosetta Plasma Consortium (RPC) with an unprecedented long-term view of the near-nucleus cometary plasma environment of an intermediately active comet. The observations revealed a highly variable and dynamic plasma environment, where spatial inhomogeneities, temporal variations and kinetic effects come together to form a formidable natural laboratory for plasma physics.

Among the many interesting observations in the plasma environment of 67P are several different types of plasma waves, including ion-acoustic waves, lower-hybrid waves, mirror mode waves and more. Here, we present observations of yet another plasma wave phenomenon in the coma of 67P, in the form of large-amplitude, quasi-harmonic density fluctuations with associated magnetic field oscillations, found in the region surrounding the diamagnetic cavity, a magnetic-field free region in the inner-most part of the coma into which the interplanetary magnetic field cannot reach. We determine properties of these waves from density and magnetic field measurements, discuss possible wave modes in the context of linear homogeneous wave theory and speculate about possible generation mechanisms in the form of drift and velocity space instabilities.