In a new twist in a landmark exploration, Europe's comet-chasing Rosetta mission has found that its target, 67P/Churyumov-Gerasimenko, has no magnetic field, scientists reported on Tuesday.
A robot lab sent down to the Comet 67/P last November found no evidence that its nucleus was magnetised, they said.
The finding could sweep away a key theory on the formation of comets and other Solar System bodies, said investigator Hans-Ulrich Auster.
"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 metre (3.25 feet) in size," he said.
The finding was published in the journal Science and presented simultaneously at a meeting of the European Geosciences Union in Vienna.
It was based on measurements sent home by the washing machine-sized lab, Philae, which Rosetta lowered onto the comet's surface last November.
The landing did not go smoothly -- a mishap that turned out to be a boon for magnetic measurements, said the team.
The probe, which weighs 100 kilogrammes (220 pounds) on Earth but less than a feather in the comet's weak gravity, bounced off the hard surface a few times before settling at an angle in a dark ditch.
"This complex trajectory turned out to be scientifically beneficial to the ROMAP team," said a European Space Agency (ESA) statement, referring to the onboard instrument Rosetta Lander Magnetometer and Plasma Monitor.
"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," added Auster.
Philae had enough stored battery power for 60 hours of experiments. It sent home reams of precious data before going into standby mode on November 15.
From analysis of the data, "we conclude that Comet 67P/Churyumov-Gerasimenko is a remarkably non-magnetic object," said Auster.
Comets are clusters of primordial dust and ice orbiting the Sun star in elliptical circuits.
The 1.3-billion-euro ($1.4-billion) Rosetta mission hopes to unlock some of the secrets of comets, which some astrophysicists believe may have "seeded" Earth with some of the ingredients for life.