We report the detection of CoRoT-18b , a massive hot jupiter transiting in front of its host star with a period of 1.9000693 \pm 0.0000028 Â days .
This planet was discovered thanks to photometric data secured with the CoRoT satellite combined with spectroscopic and photometric ground-based follow-up observations .
The planet has a mass M _ { p } = 3.47 \pm 0.38 \mathrm { M } _ { Jup } , a radius R _ { p } = 1.31 \pm 0.18 \mathrm { R } _ { Jup } , and a density \rho _ { p } = 2.2 \pm 0.8 g/cm ^ { 3 } .
It orbits a G9V star with a mass M _ { \star } = 0.95 \pm 0.15 M _ { \odot } , a radius R _ { \star } = 1.00 \pm 0.13 R _ { \odot } , and a rotation period P _ { rot } = 5.4 \pm 0.4 days .
The age of the system remains uncertain , with stellar evolution models pointing either to a few tens Ma or several Ga , while gyrochronology and lithium abundance point towards ages of a few hundred Ma .
This mismatch potentially points to a problem in our understanding of the evolution of young stars , with possibly significant implications for stellar physics and the interpretation of inferred sizes of exoplanets around young stars .
We detected the Rossiter-McLaughlin anomaly in the CoRoT-18Â system thanks to the spectroscopic observation of a transit .
We measured the obliquity \psi = 20 ^ { \circ } \pm 20 ^ { \circ } ( sky-projected value \lambda = -10 ^ { \circ } \pm 20 ^ { \circ } ) , indicating that the planet orbits in the same way as the star is rotating and that this prograde orbit is nearly aligned with the stellar equator .