In what could rank as one of the major astronomical discoveries this century, scientists have captured what may be the first direct image of a planet outside our solar system.
Discovered by a team of astronomers using the Hubble telescope to peer into deep space, the candidate planet appears as a point of light at the end of a glowing filament of dust in the Taurus constellation. Two to three times as massive as Jupiter, the cosmic body lies an estimated 450 light years away near a binary star system.
While the scientists, led by astronomer Susan Terebey, must make more observations, they say that if the object is indeed a planet, it would afford them the unprecedented opportunity to study a planet outside the solar system in detail. The object's apparent youth suggests that conventional wisdom about how planets form may need revising, they add.
"This is unbelievably exciting, seeing a possible extrasolar planet for the first time," said Alan Boss, an astrophysicist with the Carnegie Institution in Washington.
The announcement of the discovery yesterday comes on the heels of several other developments in astronomy this week:
* A spacecraft orbiting Mars has detected evidence of hematite - a mineral that, on Earth, usually needs water to form. The discovery is "the first evidence" that Mars once had massive hydrothermal activity and maybe a large body of water, says Philip Christensen of Arizona State University at Tempe, who leads the research team.
* Also on Mars, the spacecraft discovered dark deposits at the bottom a nonpolar crater that scientists say could be frozen mud or sand - suggesting that ice is present or was once there. No ice has ever been found outside the planet's polar ice caps.
* The Galileo craft orbiting among Jupiter's moons has been reporting unusual magnetic activity on Jupiter's two large moons, Europa and Callisto. The data may provide further evidence of the existence of something like our salty oceans. Research team member Margaret Kivelson with the University of California at Los Angeles admits "that's speculation." But she adds that near-surface or subsurface oceans make "very good sense" with the magnetic effects Galileo is seeing.
While scientists have suspected for some time that there's liquid water on Europa, researcher David Stevenson of the California Institute of Technology in Pasadena calls it "astounding" that Callisto should show this "ocean" effect. He says the moon "looks [geologically] dead." Water could exist deep below the surface, where pressure would lower water's freezing temperature substantially, he says. If that is the case, he adds, "I believe Ganymede [another large moon] has an ocean as well."
THE most distant discovery, however, may be the most intriguing. Until now, detecting planets around other stars has been notoriously difficult. Stars far outshine any light reflected from planets, and planet hunters have been forced to locate their quarry by, in effect, watching bushes tremble. They detect extrasolar planets by looking for their gravitational effects on the parent star's motion. This method yields clues about a planet's size and orbit. But it allows for little more than guesses about the planet's composition.
As a result, astronomers have been pinning their hopes for direct sightings of extrasolar planets on a new generation of space-based telescopes now on the drawing boards.
Dr. Terebey's discovery suggests that they may not have to wait that long. Current theories hold that while giant planets are young, they are warmed enough by their own gravity and by other processes that they glow fairly brightly in the infrared. And some binary star systems - which host half of the eight extrasolar planets detected so far - eject less-massive objects from their midst.
This means extrasolar planets could well be accessible to current technology if researchers know where to look.
The young protoplanet - perhaps only 300,000 years old - also challenges longstanding ideas about how planets form and suggests that some planets may be wandering through the galaxy without a sun to warm them.
Conventional wisdom holds that giant Jupiter-like planets form over 10 million years, slowly building from dust, then gas. But the new object, given the name TMR-1C, points to a much faster evolution directly from a rotating disk of gas and dust, according to Dr. Boss.