Sunday, January 10, 1999 Published at 07:17 GMT
New planets discovered
The newly-found planets are like Jupiter
Astronomers in the United States have discovered two new planets outside the Earth's solar system.
It is only recently that astronomers have begun to find "extra-solar" planets, but they say they expect to find many more in the coming months.
Researchers led by Debra Fischer of San Francisco State University started looking for planets around 200 stars last summer using the Lick telescope in California and the Keck telescope in Hawaii.
The first planet was discovered around star HD-195019 in the Delphinus Constellation.
It has a mass around 3.5 times that of Jupiter and is some 13.5m miles (21m km) from its sun - less than a fifth of the distance between the Earth and the sun. It completes its orbit in just 18 days.
The second is much closer in mass to Jupiter, but is even closer to its star, HD-217107, which is located in the Pisces constellation. It completes an orbit every seven days.
Neither can be seen, but they can be inferred by the gravitational pull they exert on the stars they circle. Stars with big planets around them have a distinctive wobble detectable from Earth.
Search for Earth-like planets
Dr Fischer told the American Astronomical Society she was hopeful of finding more planets.
"I think that we're smarter than we were about how to find planets," she said, "With a sample of suitable stars and enough telescope time, we expect to find planets around about 5% of sun-like stars within a few months."
Dr Fischer said the hunt for solar systems that might contain Earth-like planets would continue.
"We want smaller planets that are farther away from their host stars, because we want to probe the habitable zone of stars - the place where life may form," she said.
The first planets ever known outside our solar system were discovered in 1991 and confirmed in 1994. Penn State professor of Astronomy Alexander Wolszczan found three planets - two similar in mass to the Earth - orbiting a pulsar in the constellation of Virgo.