What made the comet sing?

This blog post is contributed by Bárbara Ferreira, EGU Media and Communications Manager. Late last year the Rosetta Plasma Consortium (RPC) announced that Comet 67P/Churyumov-Gerasimenko, which ESA’s Rosetta spacecraft has been studying in detail since August 2014, was singing in space. Now, in a paper published in the European Geosciences Union’s open access journal Annales Geophysicae, the RPC team reveals more details about 67P/C-G’s song, including why the comet was singing. The sounds ‘emitted’ by 67P/C-G are oscillations in the magnetic field around the comet. Its space environment is permeated by the solar wind – a continuous stream of electrically charged gas (called plasma) and magnetic field lines strung along from the Sun – which interacts with the comet’s gas-dust atmosphere. A consequence of this interaction is an induced cometary magnetosphere. In other words, even though the nucleus of 67P/C-G has no magnetic field of its own (as announced at this year’s EGU General Assembly), the comet’s atmosphere or coma is magnetised. As reported in Annales Geophysicae, the RPC magnetometer on Rosetta started to detect large-amplitude fluctuations in this magnetic field upon arrival of the spacecraft at the comet on 6 August 2014. For four months, until November 2014, the RPC team detected about 3000 cases of wave activity with frequencies of about 40 millihertz. “This is exciting because it is completely new to us. We did not expect this and we are still working to understand the physics of what is happening,” said RPC principal investigator Karl-Heinz Glassmeier at the time ESA reported the discovery of the ‘singing comet’ waves on the Rosetta blog. Glassmeier is Head of Space Physics and Space Sensorics at the Technische Universität Braunschweig, Germany, and the senior author of the Annales Geophysicae paper. This observation took the team somewhat by surprise because it is […]

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