image: Magnetic field data collected by Philae's ROMAP instrument immediately before (top) and after (bottom) the cliff collision at 16:20 GMT on Nov. 12, 2014 (onboard spacecraft time), between the first and second touchdowns. Height above the surface is plotted on the x-axis and magnetic field strength on the y-axis. Therefore time runs left-to-right for the ascent (lower) plot, but right-to-left for the descent (upper) plot. The measurements (crosses) are compared with a hypothetical model (solid line) assuming a slightly magnetized surface. Also included is the strength of and variation in the external field, namely the influence of the solar wind interplanetary magnetic field near the comet nucleus. At distances of 10 m or greater from the surface, the surface component would be very weak, leaving just the external field, as measured. But closer to the surface, the comet's own field should increase and dominate. That is not seen, therefore the data suggest that at scales of greater than one meter (the resolution of the instrument), the comet is not magnetized. This material relates to a paper that appeared in the April 17, 2015 issue of Science, published by AAAS. The paper, by H.-U. Auster at Technische Universität Braunschweig in Braunschweig, Germany, and colleagues was titled, 'The nonmagnetic nucleus of comet 67P/Churyumov-Gerasimenko.' view more
Credit: [Credit: ESA / Data: Auster et al. (2015) / Background comet image: ESA/Rosetta/NAVCAM - CC BY-SA IGO 3.0]