UPSILON ANDROMEDAE Image: San Francisco State University NEW SOLAR SYSTEM, revealed by analysis of 11 years of Doppler spectroscopy data, contains three Jupiter-like planets. The innermost, designated b, was first detected in 1996. It contains three quarters of the mass of Jupiter and is so close to the star (0.06 AU) that it zips around it in a circular orbit every 4.6 Earth-days. The two outer planets are both new discoveries and have elliptical (oval) orbits. The middle planet, c, has twice the mass of Jupiter and takes 242 Earth-days to complete an orbit at a distance of approximately 0.83 AU from the star. The outermost planet, d, weighs in at the mass of four Jupiters and completes one orbit every 3.5 to 4 Earth-years at a distance of 2.5 AU. The dashed red lines represent the orbits of Mercury, Venus, Earth and Mars for comparison.

The great voyages of discovery shrank our planet from a fearsome void to a familiar orb. More recently, explorations of the planets, moons, comets and asteroids in the solar system have reduced our turf in the cosmos to a relatively cozy corner.

Now it's the Milky Way's turn. The announcement on April 14 that a nearby star known as Upsilon Andromedae, quite like our Sol, sports a trio of planets, carries with it the long-sought conclusion that our tiny neighborhood may not be a cosmic quirk--there are other solar systems. As a result, the galaxy has grown a bit smaller, but a new vista, comparing ourselves to these significant others--call it comparative solar systems--has opened to us.

The discovery of the first multiple planet system ever found around a normal star, other than the nine planets in our solar system, was revealed in a joint press conference in San Francisco by two independent research teams. "We are witnessing the emergence of a new era in human exploration," said Geoffrey W. Marcy , an astronomer from San Francisco State University, whose team has identified most of the 20 extrasolar planets found so far. "We are embarking on a reconnaissance of planets around other stars in our own Milky Way Galaxy."

It was a group headed by Marcy and his colleague R. Paul Butler, now a staff astronomer at the Anglo-Australian Observatory, that first found evidence of an extrasolar planet orbiting Upsilon Andromedae--a star 44 light-years away from Earth that is roughly three billion years old, two thirds the age of the sun--in 1996. Using the telescope at the Lick Observatory near San Jose, Calif., and a technique known as Doppler spectroscopy, which detects planets orbiting distant stars by their gravitational effects on the host star's velocity, they reported that an object with three quarters of the mass of Jupiter was zipping around the star every 4.6 Earth-days in the extremely close orbit of only 0.06 astronomical units (the distance from Earth to the sun, or about 93 million miles).

But when the astronomers looked at the data over a longer period of time, they observed that there were a large number of data points that did not fit the predicted curve. This "noise" indicated that there could be an additional object circling Upsilon Andromedae. The San Francisco State researchers notified other astronomers and set to work to find the answer by analyzing 11 years of spectrographic data collected by Lick Observatory. Meanwhile a group at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and the High Altitude Observatory in Boulder, Colo., had been studying Upsilon Andromedae for more than four years with data collected by the Smithsonian's Whipple Observatory near Tucson, Ariz.