A newly discovered planet seems to have a surprisingly powerful influence on its parent star, forcing the star to rotate at exactly the same rate as the planet orbits. The planet鈥檚 day is also the same length, so the pair are fixed in a face-to-face whirl.
The puzzle is how this planet, called COROT-Exo-4b, could have so dominated the vastly larger star, which is bigger than our Sun.
The new planet was discovered by the European satellite, launched in 2006, which searches for transits 鈥� the telltale dimming of stars caused by planets passing in front of them. From the dimming effect on the light of its star, the COROT team worked out that that Exo-4b is roughly the size of Jupiter.
Advertisement
It is fairly close to its parent star, taking only 9.2 days to orbit, but that still puts it further out than most 鈥渉ot Jupiters鈥�. The planet seems too distant to have such a strong influence on the star, says astronomer of the University of Exeter, UK.
Aigrain presented the discovery yesterday at a in St Andrews, Scotland.
The planet鈥檚 gravity will raise tides in the fluid body of the star, which would very gradually synchronise the planet鈥檚 orbit and the star鈥檚 rotation 鈥� but not within the billion-year lifetime of the system. 鈥淚t would take longer than the age of the universe,鈥� Aigrain told New 杏吧原创.
Instead, the system might have started out that way. 鈥淚t could be a coincidence, but I don鈥檛 like explanations based on coincidence,鈥� 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.
