Scientists Find Building Blocks Of Earth-Like Planets
From: Stig_Agermose@online.pol.dk (Stig Agermose)
Date: Wed, 13 Aug 1997 20:02:36 -0800
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Found at
http://www.sfgate.com/cgi-bin/chronicle/article.cgi?file=MN33933.DTL&dir
ectory=/chronicle/archive/1997/08/07
Thursday, August 7, 1997 … Page A11 ©1997 San Francisco Chronicle
Scientists Report Finding Building Blocks of Planets
Clues contained in gas-rich disk orbiting new star
Charles Petit, Chronicle Science Writer
California astronomers today are reporting the discovery of what looks
like an immense construction zone for new planets some 450 light-years
from Earth.
Combining signals from half a dozen radio telescopes, scientists claim
to have found a gas-rich disk of material rotating around a young star
known as MWC480 in the constellation Taurus.
Thin disks of dust have been known to exist around older stars. The new
discovery, reported in today's issue of the journal Nature, marks the
first time the phenomenon has been detected around a very young star --
an age when planets such as those in the sun's solar system could first
be forming.
The newly found disk is also denser, and far richer in gas such as the
hydrogen that makes up most of Jupiter, than previously known disks
around stars.
"We are seeing for the first time a place where conditions are perfect
for the formation of planets like Jupiter or the Earth,'' said Anneila
Sargent, director of the Owens Valley Radio Observatory and a professor
at the California Institute of Technology in Pasadena, which operates
the observatory east of the Sierra near the Nevada border.
The star has a mass about twice that of the sun. It is just a few
million years old, about a thousandth the age of the 4.5
billion-year-old sun.
The new sighting bolsters the view that planets form easily, and often,
around stars, and that Earth and its eight sister planets in the solar
system are not the result of some fluke combination of events.
Sargent said the finding is "a perfect fit'' with theoretical
predictions about places where planets agglomerate.
The paper's lead author, postdoctoral scholar Vince Mannings, called
the disk "a planetary construction site.'' Still, he conceded, the new
observations are not proof of how worlds form, because the instruments
have not been able to spot any actual newborn planets floating in the
gas and dust around MWC480.
Although the star is well known to astronomers, the big disk became
clear to the Caltech team only with the help of instruments finely
tuned to the emission frequency of carbon monoxide.
The gas makes up only a tiny fraction of the cloud but is the most
easily detected. Most of the material is probably hydrogen gas.
The disk's outer edge is more than 30 billion miles across, or about 10
times larger than the orbits of Neptune and Pluto, and reaches almost
to the surface of the star itself in a flat sheet of material orbiting
above the star's equator, Sargent said.
So far, the disk appears to be an oblong blob. Analysis of the spectrum
of its radiation, which lets the astronomers measure its motions, shows
the gas is in a flat sheet tilted at about a 30-degree angle as seen
from Earth. It appears to orbit around the star rather than falling
into it or forming a spherical cloud around it.
The observation was welcomed by other astronomers.
"This really is consistent with our concept of solar system
formation,'' said Douglas Lin of the University of California at Santa
Cruz, an expert on planet evolution theories. "So I am not too
surprised by these results. The important thing now is to get higher
resolution (sharper focus) to see more of the physical conditions.''
The disk is presumably a leftover from the process of gravitational
collapse of interstellar gas clouds that formed the star itself. But
young stars are so boisterous, spraying strong winds of superheated gas
outward and glowing in intense ultraviolet radiation, that it seemed to
many astronomers they would blow away any disks of orbiting gas too
fast for planets to form in them.
The new observation seems to confirm that, as theorists had hoped, the
disks last long enough to spawn planets.
Sargent said one goal now is to use even more radio telescopes, from
locations farther apart on Earth, to improve the focus and look for
gaps in the rings. Such gaps would indicate where planets are forming
and clearing out the gas and dust.
Several teams of astronomers in recent years have found indirect
evidence of actual planets around stars similar to the sun. But to see
how such planets first form, "we need to catch them in their early
stages. That is what we think we are doing now,'' Sargent said.
© The Chronicle Publishing Company
Index: Extra-Solar Planets
Created: Aug 13, 1997
