SANTA CRUZ, Calif., Dec. 1 -- Researchers from the University of California - Santa Cruz, Washington, D.C.'s Carnegie Institution, and the University of Sussex, England, have identified six new planets orbiting nearby stars. This discovery raises the total number of planets detected outside the solar system to 28. According to Steven Vogt, professor of astronomy and astrophysics at UC - Santa Cruz, evidence also suggests that two previously discovered planets have additional companions.The team of astronomers made the discoveries using the High-Resolution Echelle Spectrograph (HIRES) on Hawaii's Keck I Telescope. For the past three years, the researchers have been using the facilities at the W.M. Keck Observatory to search for planets around 500 nearby Sun-like stars. Support for this project has been provided by the National Science Foundation and by NASA's Origins Program, which has supplied both funding and telescope time.The scientists report that the newly identified planets orbit stars that are between 65 and 192 light-years from Earth, and similar in size, age, and brightness to the Sun. The planets range in mass from slightly smaller to several times larger than the planet Jupiter -- 0.8 to 6.5 times Jupiter's mass. Vogt noted that the composition of the planets is likely to resemble that of Jupiter as well; astronomers suppose them to be essentially giant balls of hydrogen and helium gas.