Evidence of Earth-like planets
2007-08-17 07:41
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.
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.
Extraterrestrial life?
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 harbour
water and perhaps life.
A light year is about 10 trillion km, 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 200km 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 five 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.