At http://phys.org/print348212853.html … we learn that magnetic field data collected by the Philae lander and transferred back to Rosetta shows the comet itself is not magnetised. However, Philae was only beaming back information for a short period before being bounced back into its hidey hole – where it has yet to awake.
The data appears to be significant as the astronomers appear to have suspected the comet might have its own magnetic field. This idea arrives from theory rather than fact as magnetic fields are thought to have coincided with the process of accretion during the early solar system. What was originally a swirling disc of gas and dust gave birth to the Sun – and the leftovers formed asteroids, planets, and comets. The dust is thought to have contained iron, in the form of magnetite. Meteorites can contain millimetre sized grains of magnetic material – and comets are thought to have a similar make-up. Seems like fact is interfering with theory – and there might be a few surprises in store over the next few months (if only Philae would awake).
The research is published in the journal Science – www.sciencemag.org/doi/10.1126/science.0005102
At www.sciencenews.org/article/comet-67p-shows-no-sign-of-magnetism … begins with … 'if astronauts go walk about they can leave their compasses at home …' referring to the comet, Churyumov-Gerasimenko. It is hard to see how magnetism helped assemble comets, it goes on, and other small planetary rocks. It now emerges that the Giotti spacecraft also failed to find a magnetic field when it flew within 600km of Comet Halley in 1986