SAN DIEGO, Jan. 9 ?Astronomers have discovered two more planetary systems in the universe, and they appear to bear little or no resemblance to each other or to the solar system.

In one of the systems, a Sun-like star is accompanied by a massive planet and an even larger object 17 times as massive as Jupiter. If this whopper is a planet, it is the largest ever detected, defying current theory.

In the other system, two planets of more normal size are orbiting a small star. But their orbits are anything but normal. The pair of planets are locked in resonant orbits, moving in synchrony around the star with orbital periods of 61 and 30 days; the inner planet goes around twice for each orbit of the outer one.

"They are unique and frightening," the discovery team's leader, Dr. Geoffrey W. Marcy of the University of California at Berkeley, said of the newfound planetary systems. "We thought we understood the mass ranges of planets of other stars. We thought we understood the full diversity of planets."

The discovery compounded the perplexity and confusion raised by earlier detection of planets beyond the Sun's family, beginning in 1995. Of more than 1,000 stars observed, over 50, all relatively nearby Earth, have so far been found to be accompanied by single planets.

The first multiplanet system to have been discovered ?and until now the only one ?was found two years ago, and its three Jupiter-class planets are orbiting much closer to their star, Upsilon Andromedae, than Jupiter is to the Sun.