Astronomers Detect Signs That Jupiter Has Distant Cousin
Astronomers for first time find planetary system of distant star that resembles Sun's family of planets in significant respects; host star of planetary system, 55 Cancri, is much like Sun in age and size; it has newly detected planet that resembles Jupiter in mass and, of greater importance, has orbit almost same as Jupiter's; in dynamics of solar system, Jupiter is pivotal in setting up conditions conducive to live on Earth; astronomers say it is not inconceivable that somewhere between Jupiter-like planet and its star orbits an Earth-like planet; findings are announced by Dr Geoffrey W Marcy of University of California at Berkeley, who led team, at news conference at National Aeronautics and Space Administration; drawing (M)