Three huge planets are spinning around the star Upsilon Andromedae, 44 light years from Earth in our Milky Way galaxy, researchers from San Francisco State University and Harvard announced Thursday.
It is the best evidence yet, scientists say, that we are not alone. One of the discoverers says it's an age-old question: Is our solar system the only one?
"And for the first time we have an answer," says Geoffrey Marcy of San Francisco State University. "We've finally found a full family of planets like our own - this one around another star."
The announcement marks a major advance in the discovery of planets around distant stars.
But the solar system is not exactly like our own. Three huge planets the size of Jupiter are in orbit around the star. One hovers so close to Upsilon Andromedae that its year lasts only four-and-a-half days.
"So it's almost skimming the surface of the star," says Marcy. "It's a very close Jupiter."
|An illustration shows the star Upsilon Andromedae at far left, and its farthest-orbiting planet at far right. The second-closest planet appears as a dot within the star's glow. Not visible in this image is the third planet, a speck closely orbiting the star. (AP)|
The planet, spotted in 1996, has at least 75 percent of the mass of Jupiter. Jupiter is the largest planet in the solar system, 318 times the size of Earth.
The middle planet is twice Jupiter's mass and orbits the star every 242 days from a location about as far as Venus from the sun. The outer planet has the mass of four Jupiters and orbits its star every 3 and 1/2 to 4 years. It is more than twice as far from its star as Earth is from the sun.
The researchers began their search for planets 12 years ago. They and their colleagues are responsible for finding 14 of the 20 planets known to exist outside the Earth's solar system.
However, those planets were single bodies surrounding a star. This is the first time multiple planets around a star have been found.
Earthlike planets are unlikely to be found in such systems, the scientists said, because the forces generated by huge Jupiterlike planets moving in elliptical rather than circular orbits would kick smaller planets out into oblivion.
But if there are other solar systems out there, there may well be other Earths.
"Those Earths could harbor life," Marcy says. "And so the stock, if you will, in life in the galaxy has just shot up enormously."
The planets were discovered using a method that measures their gavitational pull on their star, not by direct observation.
Planets' gravity tugs on their stars, causing them to wobble slightly. By examining the star's ultraviolet light transmissions, astronomers can calculate back-and-forth shifts in the ultraviolet wavelengths. A larger wobble indicates the orbiting planet is large.
"I am mystified at how such a system of Jupiterlike planets might have been created," Marcy told the Associated Press on Thursday.
"This will shake up the theory of planet formation."
And with 200 billion stars in the galaxy, astronomers have plenty of places to look for another family of planets like our own.