This leads scientists to believe that magnetic fields threading through the proto-planetary disc could have played an important role in moving material around as it started to clump together to form larger bodies.
Because comets contain some of the most pristine materials in the solar system, they offer a natural laboratory for investigating whether or not these larger chunks could have remained magnetized. However, detecting the magnetic field of comets has proven difficult in previous missions, which have typically made rapid flybys, relatively far from comet nuclei.
Philae's magnetic field measuring instrument is the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP), while Rosetta carries a magnetometer as part of the Rosetta Plasma Consortium suite of sensors (RPC-MAG).
Changes in the magnetic field surrounding Rosetta allowed RPC-MAG to detect the moment when Philae was deployed in the morning of Nov. 12, 2014.
"The unplanned flight across the surface actually meant we could collect precise magnetic field measurements with Philae at the four points we made contact with, and at a range of heights above the surface," said lead author Hans-Ulrich Auster, co-principal investigator of ROMAP, according to a press release.
"If the surface was magnetized, we would have expected to see a clear increase in the magnetic field readings as we got closer and closer to the surface," Hans-Ulrich said. "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."
Instead, the magnetic field that was measured was consistent with an external one, namely the influence of the solar wind interplanetary magnetic field near the comet nucleus. According to the press release, this conclusion is confirmed by the fact that variations in the field that were measured by Philae closely agree with those seen at the same time by Rosetta.
"During Philae's landing, Rosetta was about 17 km above the surface, and we could provide complementary magnetic field readings that rule out any local magnetic anomalies in the comet's surface materials," said co-author Karl-Heinz Glassmeier, principal investigator of RPC-MAG, according to the press release.
"If any material is magnetized, it must be on a scale of less than one meter, below the spatial resolution of our measurements. And if Comet 67P/Churyumov-Gerasimenko is representative of all cometary nuclei, then we suggest that magnetic forces are unlikely to have played a role in the accumulation of planetary building blocks greater than one meter in size," concluded Hans-Ulrich, according to the press release.
"It's great to see the complementary nature of Rosetta and Philae's measurements, working together to answer this simple, but important 'yes-no' question as to whether the comet is magnetized," said Matt Taylor, ESA's Rosetta project scientist.
Reference:
"The non-magnetic nucleus of Comet 67P/Churyumov-Gerasimenko," H.-U. Auster et al., Science Express, 14 April 2015 [https://www.sciencemag.org/content/early/2015/04/13/science.aaa5102]. The results were also presented on 14 April at the European Geosciences Union (EGU) General Assembly 2015 in Vienna, Austria, during a dedicated Rosetta mission press briefing.
