March 27, 2007
(PLANETQUEST) -- Two teams of astronomers have announced the discovery of four gas-giant planets around other stars, bringing the total number of known extrasolar planets to 204.
Among the new planets, one is roughly the same mass as Neptune, putting it in a relatively new class of lower-mass planets that recently have been detected. The planet orbits the star HD 219828, located 264 light-years away in the constellation Pegasus.
The planet is located at 0.052 AU from its star, closer than Mercury is to the sun, and it completes an orbit in just under four Earth days. It is the 11th Neptune-mass planet to be found orbiting a sun-like star.
A separate European team has announced the discovery of three new gas-giant planets, ranging in size from slightly larger than Jupiter to more than three times Jupiter's mass. These planets are located around the stars HD 100777, 172 light-years away; HD 190647, 176 light-years away; and HD 221287, 172 light-years away.
All of the new planets were discovered using the High Accuracy Radial velocity Planet Searcher (HARPS), part of the European Southern Observatory in La Silla, Chile. The HARPS instrument is a high-resolution spectrograph that detects planets indirectly, using the radial velocity method, which measures the back-and-forth wobble of a star induced by the gravitational tug of its planetary companion. The majority of extrasolar planets discovered so far have been detected using this method.
