Listen to it! That's Comet 67P/Churyumov-Gerasimenko singing. This cosmic song was just discovered by the European Space Agency, which released the soundtrack for our enjoyment. It's totally new and unexpected, say the scientists who will remotely land a probe on the rocky surface of the comet tomorrow.

The ESA reports:

Rosetta's Plasma Consortium (RPC) consists of five instruments on the Rosetta orbiter that provide a wide variety of complementary information about the plasma environment surrounding Comet 67P/C-G. [...] The instruments are designed to study a number of phenomena, including: the interaction of 67P/C-G with the solar wind, a continuous stream of plasma emitted by the Sun; changes of activity on the comet; the structure and dynamics of the comet's tenuous plasma 'atmosphere', known as the coma; and the physical properties of the cometary nucleus and surface.

But one observation has taken the RPC scientists somewhat by surprise. The comet seems to be emitting a 'song' in the form of oscillations in the magnetic field in the comet's environment. It is being sung at 40-50 millihertz, far below human hearing, which typically picks up sound between 20 Hz and 20 kHz. To make the music audible to the human ear, the frequencies have been increased by a factor of about 10,000.

The music was heard clearly by the magnetometer experiment (RPC-Mag) for the first time in August, when Rosetta drew to within 100 km of 67P/C-G. The scientists think it must be produced in some way by the activity of the comet, as it releases neutral particles into space where they become electrically charged due to a process called ionisation. But the precise physical mechanism behind the oscillations remains a mystery.

"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," says Karl-Heinz Glaßmeier, head of Space Physics and Space Sensorics at the Technische Universität Braunschweig, Germany.

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I am shuffling through the comet's song for the fifth or sixth time, and I'm still in awe. It sounds like a space dolphin. A living thing. Also, I just found a new ringtone for my phone. [ESA]