The milestone comes just four years after the first indirect evidence of a planet beyond our solar system was announced. The astronomers' method involves measuring reflected light from the star around which the huge planet orbits.

The planet is estimated to have a diameter roughly 1.6 to 1.8 times Jupiter's and is about eight times as massive. First discovered by indirect observations in 1997, the newly measured object orbits a star called Tau Bootis.

 The planet is said to be blue-green in color.

The study, appearing in Thursday's (December 16) issue of the journal Nature, is the second in the past month to confirm the existence of huge extrasolar planets. Tennessee State University astronomer Greg Henry announced in November the detection of a planet by measuring a slight drop in light emitted from a host star as the planet's orbit brought it in front of the star.

Prior to Henry's work, planets around other stars have been detected only by indirect means: Scientists watch a star for a slight wobble, which indicates a planet may be exerting a gravitational pull on the star. Those who employ the method have been waiting for independent confirmation that it works -- that the 30 or so planets it has been used to find are in fact planets (and not evidence of some other, unknown gravitational influence on the host stars).