October 12, 2005
(OBSERVATOIRE DE HAUTE-PROVENCE) -- An international team of astronomers has announced the discovery of a new transiting extrasolar planet. The planet HD189733b, in the constellation Vulpecula, was detected and studied by the combination of two different methods, radial velocities and photometric transits, using the telescopes at Haute-Provence Observatory (OHP). It is one of the few extrasolar planets for which scientists have been able to accurately determine both its radius (1.26 Jupiter radii) and mass (1.15 Jupiter masses).
This new extrasolar planet, located about 63 light-years from Earth, joins the very exclusive group of planets outside our solar system that scientists have been able to measure precisely. Although more than 150 extrasolar planets are presently known, accurate values for masses and radii are known only for nine systems. HD189733b has a mass 365 times that of the Earth and a radius 14 times larger. Its density is comparable to that of Saturn. The star HD189733 is located by in the vicinity of the famous M27 "Dumbell" planetary nebula, and can be seen using binoculars (visual magnitude 7.7).
Its orbital period is one of the shortest known (only 2.2 days), nearly 2000 times faster than Jupiter, which takes 12 years to make a trip around the Sun. Due to the favorable orientation of its orbital plane, the planet HD189733b occults the central star every 2.2 days, producing a photometric transit (analogous to the Venus transit of the Sun seen in June 2004), a small decrease of flux lasting 2 hours.
