Scientists have announced that comet 67P/Churyumov-Gerasimenko is non-magnetised in the first set of results from the Philae lander.
The Philae lander, carrying an array of scientific instruments, detached from the European Space Agency’s Rosetta spacecraft in November 2014. It landed on comet 67P/Churyumov-Gerasimenko after a descent of several hours to start analysing the comet’s surface and atmosphere.
Some of the first results of these investigations are published today in Science. The spacecraft and lander used magnetometers to measure the comet's magnetism and these determined that it had no detectable magnetic field, despite other small solar system objects showing magnetism.
This is quite surprising, since we have moon rock samples and meteorites which show more magnetism than 67P.
– Chris Carr
Imperial College London is involved in the Plasma Consortium of instruments on the Rosetta spacecraft, which provided measurements in support of the lander magnetometer. Chris Carr, of the Department of Physics, said: “There may be some minerals in the body of the comet that are magnetised, creating detectable signals on scales smaller than we can measure, but the results show there is no regular magnetic field on a metre-scale.
“This is quite surprising, since we have moon rock samples and meteorites which show more magnetism than 67P. So we might describe 67P as ‘remarkably non-magnetic’.”
Comets are extremely old and pristine objects, left over from when the solar system formed 4.6 billion years ago. If comets were magnetised, it might help explain how some of the early building blocks of the solar system began to clump together. However, the discovery on 67P suggests it’s unlikely that magnetism played a role in the aggregation of solar-system bodies such as comets.
First surface data
Previous comet flyby missions had failed to detect magnetic fields, but the only way to know for sure is a measurement on the surface. Magnetic fields fall off rapidly with distance, in the same way that a magnet has to be very close to an object to attach to it.
Carr said: “This is the first experimental data from an instrument physically on the surface of a comet. As far as we can tell there’s no magnetic field, not even a hint.”
The analysis was led by scientists from the Technische Universität Braunschweig in Germany. Co-author Dr Hans-Ulrich Auster said: “If the surface was magnetised, we would have expected to see a clear increase in the magnetic field readings as we got closer and closer to the surface. But this was not the case at any of the locations we visited.”
Co-author Professor Karl-Heinz Glassmeier from the Technische Universität Braunschweig said: “We are most fascinated by the magnetic field measurements at 67P. By combining observations from both instruments we are able to confirm that the nucleus is essentially non-magnetic. It is a privilege to do science in such an environment!”
The search continues
Despite the wealth of data beamed back from Philae, the project team are still unsure exactly where the probe is on the surface of the comet. It had a bumpy landing, touching down a couple of times with high bounces in between before finally coming to a rest outside the anticipated landing zone.
Carr said that knowing the precise location will give context to any measurements made by Philae. Photographs and measurements of the actual landing site by Rosetta, which is still orbiting the comet, would provide information about the local environment and geology.
"The nonmagnetic nucleus of comet 67P/Churyumov-Gerasimenko" by Auster et al. is published in Science.
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