By Ron Cowen
With the discovery of a fifth planet circling the nearby star 55 Cancri, astronomers have found the richest—and heaviest—planetary system beyond the sun’s.
The sunlike star 55 Cancri lies just 41 light-years from Earth. Exoplanet hunters found the fifth planet by recording the tiny wobble it induces in the motion of its parent star—the same way researchers found the four other orbs. Three of those earlier finds, ranging in mass from that of Neptune to that of Jupiter, have orbits smaller than about one-tenth Earth’s distance from the sun. The fourth is about four times as massive as Jupiter and circles 55 Cancri at about Jupiter’s distance from the sun.