Vol. 569
In section 10. Planets and planetary systems

Detecting the spin-orbit misalignment of the super-Earth 55 Cancri e

by V. Bourrier and G. Hébrard A&A 569, A65


The angle between the orbital plane of planets and the equatorial plane of their parent stars may be measured during transit events, thanks to the so-called Rossiter-McLaughlin effect. Obtaining sufficient signal-to-noise ratio generally requires the planet to be Jupiter-like and the star to rotate relatively rapidly. Bourrier and Hébrard use HARPS-N to detect the effect on 55 Cnc e, a small "super-Earth" that is only 8 times more massive than the Earth, taking advantage of the brightness of the star that is visible to the naked eye and of the proximity of the planet (an orbital period of only 0.74 day). This is the first time that this has been done for a planet with such low mass and in a planetary system. (The 55 Cnc system harbors at least 5 planets.) They find that the planet's orbit is highly misaligned compared to the star's spin, which is a surprise. It remains to be seen whether this is the rule or the exception.