Hubble takes first image of possible planet.

The dim white dot that Susan Terebey and her colleagues spied in images of a nearby star-forming region could easily have been dismissed as a background star. The astronomers were intrigued, however, by the object's location--at one end of a long, luminous trail. At the other end lies a pair of newborn stars.

The team suggests that the youthful pair are parents and that the white dot is their runaway offspring--a planet with two to three times the mass of Jupiter speeding away at 10 kilometers per second. If that speculation is correct, then the images, recorded by the Hubble Space Telescope, will go down in history as the first ever taken of a planet outside the solar system. Terebey, president of Extrasolar Research Corp. in Pasadena, Calif., unveiled the pictures last week at a press briefing in Washington, D.C.

Although researchers have inferred the presence of eight planets outside the solar system, their evidence is based solely on wobbles in the motion of the stars the planets are thought to orbit.

To image the object, Hubble's near-infrared camera penetrated the dust in a star-forming region in the constellation Taurus, 450 light-years from Earth. The argument that the body, designated TMR-1C, is a planet rests on its proximity to the luminous, 200 billion-km-long trail that leads directly to the two young stars. Terebey's team says there's only a 2 percent chance that the object is a distant star that happens to lie at that position.

The researchers say the trail represents dust pushed out of the way as the planet was kicked out of its birthplace and went barreling into space. In this scenario, the planet is about the same age as the stars, a few hundred thousand years old. Given the planet's age and luminosity, theory suggests that TMR-1C has a mass several times that of the largest planet in the solar system.

Those numbers would seem to pose a puzzle, says Alan P. Boss of the Carnegie Institution of Washington (D.C.). Theorists have generally believed it takes a two-step process lasting 10 million years for a giant planet like Jupiter to form. First, bits of dust and ice lying in a disk around a young star assemble into a solid core. Then, the core snares enough gas from the disk to make a full-fledged, massive planet. In a model described by Boss in the May 14 Nature, however, parts of the disk clump directly into a large ball of gas and dust heavy enough to form a giant planet in as little as 1,000 years.

Boss' model requires that very young stars have relatively dense disks. In a report accepted for publication in Nature, Luis F. Rodriguez of the National Autonomous University of Mexico in Mexico City and his collaborators find such compact disks in a star-forming region known as L1551. Rodriguez declined to discuss the article but noted that "our results and those of Terebey et at., if fully confirmed, open new avenues in the issue of planet formation in binary systems."

Adam S. Burrows of the University of Arizona in Tucson cautions that the crudeness of stellar models and observational uncertainties make it difficult to estimate the mass and age of TMR-1C For example, if the object lies in an unusually dusty region of Taurus, its true luminosity-and mass-might be underestimated. It's possible, in fact, that the object might be massive enough to qualify as a kind of failed star called a brown dwarf.

After studying the object's spectra, researchers expect to determine whether it has the mass and composition of a star, a brown dwarf, or a planet.