Instead, the system might have started out that way. "It could be a coincidence, but I don't like explanations based on coincidence," says Aigrain. She suggests that magnetic fields might have helped to lock the system together, but stresses that it is pure speculation at this point.

During its mission, COROT should discover many more planets. Aigrain and her colleagues hope they will then have a better idea whether synchronised systems are common, and what causes the phenomenon.