Located 41 light-years away in the constellation Cancer, 55 Cancri was already known to have one orbiting planet. Geoffrey Marcy of the University of California at Berkeley, R. Paul Butler of the Carnegie Institution of Washington, D.C., and their colleagues discovered the second planet by measuring shifts in starlight caused by the gravitational pull of orbiting celestial bodies. Over the course of many years, these shifts can reveal the size, mass and period of a planet. The researchers determined that the second planet is between 3.5 and five times the mass of Jupiter and takes 13 years to circle 55 Cancri. Jupiter makes a complete trip around the sun in 11.86 years. "All other extrasolar planets discovered up to now orbit closer to the parent star, and most of them have had elongated, eccentric orbits," Marcy says. "This is the first near analogue to our Jupiter."
The scientists classified the newly discovered pair as a first cousin to our own planetary system. In fact, when Gregory Laughlin of the University of California at Santa Cruz incorporated the most recent data into a hypothetical configuration of planets, he found that an Earth-size celestial body could theoretically exist in a stable orbit between 55 Cancri's two known gas giant planets. Although that remains a point of speculation, team member Debra Fischer of the University of California at Berkeley notes that "this planetary system will be the best candidate for direct pictures when the Terrestrial Planet Finder is launched later this decade."
Among the other planet detections announced yesterday by the international collaboration was the smallest exoplanet yet discovered, circling the star HD49674 in the constellation Auriga. Forty times as massive as Earth, it circles HD49674 at a distance just one twentieth of that between Earth and the sun. The new findings bring the total of known extrasolar planets to more than 90.