Using a technique called microlensing, astronomers have discovered a new extrasolar planet, 28,000 light years distant, with a mass approximately 5.5 times that of earth. The discovery brings the number of extrasolar planets to more than 170. Alas, all seem unlikely to harbor “life as we know it.”
Most of these planets have been detected by the “wobble” or Doppler effect method. Planets with large masses and their parent stars essentially orbit a common point, “pulling” the star off center. Our own Jupiter, roughly 318 times the mass of the earth, would be an eligible candidate. Neptune, with a mass roughly 17 times that of earth, and much further from the sun than Jupiter, would not be. See graphic.
The warping of space by matter, part of Einstein’s theory of general relativity, provides planet-hunters another tool. Stars, which are typically much more massive than even the largest planets, warp space around them, like a shotput ball resting on a waterbed. Light from more distant objects is distorted by the warped space, creating a blip in a graph of light intensity (a light curve). A planet orbiting a star will create a similar, but much smaller companion blip. The new planet was found in just this way. See graphic.
An animation of how microlensing occurs, and how it relates to discovering a planet, is here at the National Science Foundation.
The new planet, somewhat unpoetically classified as OGLE-2005-BLG-390Lb, takes 10 earth years to orbit its sun, a cool red dwarf star. With an average orbital radius of 390 million km (about halfway between the orbits of Mars and Jupiter), the planet is very cold, as in -220 degrees C.
Details are here.