This isn't exactly a shocking turn of events, the researchers say, but it does help rule out magnetism having a strong pull in planetary formation.
Only a minority of researchers thought they might find a magnetic field, says [lead researcher Hans-Ulrich] Auster. The results don’t rule out the possibility that magnetism may help pull together small particles in the earliest growth phase of comets or planets. But they make it implausible that magnetism furthers the growth of bodies once they have reached a certain size, he says. The resolution of Rosetta’s magnetic field measurements is limited to about one metre. On that scale at least, magnetic forces seem to have played little, if any, role in the evolution of the comet.
And the findings are due in part to the bumpy landing that Rosetta's Philae lander had last fall. When the lander (which was the first man-made object to make a controlled landing on a comet) hit the surface it bounced several times. Bad news for Philae, which ended up in a dark spot that quickly drained its solar batteries. But it was good news for the authors of the magnetism paper, because those multiple touchdowns and take-offs gave them magnetic readings for an unexpected number of sites (and heights) across the comet.
“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,” Auster said in a statement. “But this was not the case at any of the locations we visited, so we conclude that Comet 67P/Churyumov-Gerasimenko is a remarkably non-magnetic object.”
In fact, Auster and his colleagues estimate that any magnetic field the comet possesses must be one ten-thousandth the strength of Earth's.
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