Rosetta mission has found that its target comet, 67P/Churyumov-Gerasimenko, has no magnetic field.
Measurements made by Rosetta and Philae during the probe's multiple landings on Comet showed that the comet's nucleus is not magnetised.
Hans-Ulrich Auster said that the findings could sweep away a key theory on the formation of comets and other solar system bodies.
It could mean that magnetic forces may not have played a role, as theorised by some, in a crucial stage of planet building.
The magnetic field measurements from Rosetta and Philae also showed details about how the lander bounced twice high off the surface of the comet and then rolled before settling in what was thought to be the edge of a shady crater.
But it remains unclear as to how crucial magnetic fields were later on in this accretion process, as the building blocks grew to centimetres, metres and then tens of metres across, before gravity started to dominate when they grew to hundreds of metres and kilometres in scale.
The study is published in the journal Science.