[meteorite-list] Polluted Dead Star Indicates Planets Like Earth May Have Formed Around Other Stars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 17 Aug 2007 16:42:56 -0700 (PDT)
Message-ID: <200708172342.QAA27313_at_zagami.jpl.nasa.gov>

http://newsroom.ucla.edu/page.asp?RelNum=8153

Date: August 16, 2007
Contact: Stuart Wolpert ( swolpert at support.ucla.edu )
Phone: 310-206-0511

Polluted Dead Star Indicates Planets Like Earth May Have Formed Around
Other Stars, UCLA Astronomers Report

The chemical fingerprint of a burned-out star indicates that Earth-like
planets may not be rare in the universe and could give clues to what our
solar system will look like when our sun dies and becomes a white dwarf
star some five billion years from now.

Astronomers from UCLA report that a white dwarf star known as GD 362,
which is surrounded by dusty rings similar to those of Saturn, has been
contaminated by a large asteroid that left more than a dozen observable
chemical elements in the white dwarf's atmosphere. Such an observation
is unprecedented in astronomy. Was there some kind of violent
interaction between the star and the asteroid?

The UCLA astronomers think that after about a billion years orbiting the
white dwarf as part of an ancient planetary system, an asteroid got
close enough to the star to be torn apart by its very strong
gravitational force field. An Earth-sized but exceedingly dense white
dwarf is the standard end state for most stars. This particular white
dwarf, which is under investigation by the W.M. Keck Observatory in
Hawaii, is located in the constellation Hercules, approximately 150
light-years, or 1,000 trillion miles, from Earth.

The asteroid broke apart into dust particles that orbited the white
dwarf and over time "polluted the white dwarf's atmosphere," said
Benjamin Zuckerman, UCLA professor of physics and astronomy and lead
author of the research, which has been accepted for publication in an
upcoming issue of the Astrophysical Journal, the premier journal of
astronomy.

The astronomers note that the spectroscopic observations they are
reporting constitute the first detailed assessment of the elemental
composition of an object in an extrasolar planetary system.

"The relative abundance of the elements in the white dwarf's atmosphere,
polluted by the asteroid, appears similar to those in our Earth-Moon
system," Zuckerman said.

"What we have here is a composition of the white dwarf that is fairly
similar to that of the inner planets of our solar system," said Michael
Jura, UCLA professor of physics and astronomy and co-author of the
research. "Are there other terrestrial planets like Earth in other solar
systems? This white dwarf's fingerprint is a significant advance in
demonstrating that something like terrestrial planet formation occurred
around this other star and probably occurred around other stars as well,
because it suggests the Earth's composition is not unique.

"The asteroid that is being shredded is very iron-rich and abundant in
calcium and other elements, and low in carbon, like a sturdy rock," Jura
added.

The research implies that the forces that made the Earth and our inner
solar system seem to have occurred in this system as well, and probably
around other white dwarfs too, Jura said.

Zuckerman said the research result does not rule out the possibility
that two planets in this ancient planetary system collided and the
orbiting dust and detected elements are from a piece of one of the
colliding planets rather than from a more conventional asteroid.

"Something dramatic and violent probably happened," he said.

What knocked the asteroid out of its original orbit? It probably was
deflected by the gravitational field of a large planet, Zuckerman said.

Our own planetary system looks very stable, Zuckerman said, but billions
of years from now, when the sun starts to expand in size and lose mass
rapidly, the planets and asteroids will spiral away, and the planets
closest to the sun, like Mercury and Venus, will be engulfed by the sun
and destroyed.

"But other planets, probably including the Earth and the asteroid belt
between Mars and Jupiter will spiral out, and their orbits then will
make our stable system much less stable," he said.

A third UCLA author on the paper, physics and astronomy associate
professor Brad Hansen, said, "In our solar system, objects rich in iron
formed closer to the sun than the objects rich in carbon and ice, which
formed farther away, where it is colder. This research tells us about
the origin of the asteroid, its temperature when it formed and its
chemistry - conditions similar to the Earth's."

The group of astronomers, which also includes of UCLA graduate student
Carl Melis and Detlev Koester at Germany's University of Kiel, detected
17 elements in the atmosphere of the white dwarf that probably came from
a large asteroid; the asteroid may have once been part of a larger body,
perhaps like one of the inner planets of our solar system. Many of the
elements have never before been detected in the atmosphere of a white
dwarf, including the rare elements strontium and scandium.

The gravitational field of the white dwarf is so strong that all
elements heavier than the lightest elements - hydrogen and helium -
quickly sink into the white dwarf's interior, Hansen said.

The asteroid likely broke up more than 100,000 years ago, and perhaps as
long as a million years ago, the astronomers said. The star became a
very hot white dwarf approximately 1 billion years ago and since then
has been steadily cooling off.

Unlike GD 362, most white dwarfs are pristine in their composition.

"You wouldn't notice another skyscraper in New York, but the same
skyscraper in Nebraska would stick out like a sore thumb," Hansen said.
"That's the case here. A little change in the atmosphere of a white
dwarf is very obvious."

The astronomers used the HIRES spectrometer on the Keck I Telescope to
take optical spectra of the white dwarf, spanning the ultraviolet to the
full visible range of light. Each element can be identified by its own
characteristic spectrum.

The researchers said they find it quite remarkable that even at a
distance of 1,000 trillion miles, the Keck HIRES measurements enable
them to determine minute details of the bulk composition of a relatively
tiny object - as astronomical sizes go - like an asteroid. Currently, no
other known observational technique exists that allows for such
compositional information to be obtained.

The remains of a white dwarf cool slowly over many billions of years as
the dying ember makes its slow journey into oblivion.

NASA funded the research.

UCLA is California's largest university, with an enrollment of nearly
37,000 undergraduate and graduate students. The UCLA College of Letters
and Science and the university's 11 professional schools feature
renowned faculty and offer more than 300 degree programs and majors.
UCLA is a national and international leader in the breadth and quality
of its academic, research, health care, cultural, continuing education
and athletic programs. Four alumni and five faculty have been awarded
the Nobel Prize.

-UCLA-

SW353
Received on Fri 17 Aug 2007 07:42:56 PM PDT