WASHINGTON Chemical elements observed around a burned-out star known as a white dwarf offer evidence Earth-like planets once orbited it, suggesting that worlds like our own may not be rare in the cosmos, scientists said on Thursday.
Astronomers at the University of California, Los Angeles and University of Kiel in Germany studied a white dwarf called GD 362 located 150 light-years away in our Milky Way galaxy.
They figured out the chemical composition of a large asteroid that was ripped apart by gravitational forces as it approached GD 362, finding it was similar to the Earth's crust. It was rich in iron and calcium and low in carbon, much like a strong rock, they said.
The white dwarf is surrounded by dusty rings, probably made up of objects shredded as they ventured too close.
"It's probably quite similar to Saturn's rings," UCLA astronomer Michael Jura said in a telephone interview.
GD 362 once was a star similar to the sun. After billions of years, it ballooned into a "red giant" as part of its death process, expelling most of its outer material, then degenerated into a burnt-out remnant called a white dwarf.
The fact that the asteroid is so similar in make-up to the Earth, as well as the moon, indicates that rocky planets like our own may have orbited the star eons ago, Jura said.
And if such planets currently populate our solar system and existed in a planetary system around this white dwarf, they may well be fairly common in the universe, Jura added.
The research, based on observations made using the Keck I Telescope in Hawaii, will appear in the Astrophysical Journal.
It is the latest evidence found by astronomers indicating that planets like Earth are found outside our solar system.
European astronomers in April said they detected the most Earth-like planet yet outside the solar system orbiting a star 20.5 light-years from here, with temperatures that could harbor water and perhaps life.
A light year is about 6 trillion miles, the distance light travels in a year.
Jura said that his study's fresh evidence of Earth-like planets outside our solar system lends support to the possibility of extraterrestrial life.
"It's more than just daydreams," Jura said. "It's realistic to imagine that there are other places relatively similar to the Earth which would be a habitat. But, of course, we have no evidence whatsoever that they (alien life forms) do exist."
The rocky asteroid had a diameter of roughly 125 miles (200 km) and may have been smashed by GD 362 between 100,000 and a million years ago, the astronomers said. While the white dwarf has a mass close to that of our sun, it has collapsed to such a point that its diameter is approximately that of the Earth.
GD 362 may offer a glimpse into our solar system's future. Astronomers believe the sun in perhaps 5 billion years will go through the same process, ending up as a white dwarf.
UCLA astronomer Benjamin Zuckerman said when our sun starts to expand in size and lose mass, the planets closest to the sun, Mercury and Venus, will get engulfed and destroyed. Other planets, probably including Earth, and the asteroid belt between Mars and Jupiter, will spiral out of their orbits, Zuckerman said.