A vast
collection of space pebbles surrounding a relatively nearby star is a planetary
construction zone, astronomers said today.
The star, TW
Hydrae, is young and ripe for developing new worlds.
New
observations reveal a swath of pebble-sized material extending at least a
billion miles from the star. It's just the sort of stuff theory says is needed
for making comets, asteroids and eventually planets around a young star.
"We're
seeing planet building happening right before our eyes," David Wilner of the Harvard-Smithsonian Center for Astrophysics
said Friday. "The foundation has been laid and now the building
materials are coming together to make a new solar system."
Right age
After a star
is born, it takes millions of years for a planet to form, astronomers believe.
TW Hydrae is about 10 million years old.
Only a few
sets of observations have shown the planet-formation process in
progress, and scientists have yet to witness all the phases, thereby
letting them piece together a full chain of events based not just on theory but
real evidence. It's also not
known if there is just one primary mechanism for building a planet or if
there might be two or more.
Wilner
and colleagues used the National Science Foundation's Very Large Array to
measure radio emissions from TW Hydrae. The length of the
radio waves suggest the size of particles from which they emanate.
"The
strong emission at wavelengths of a few centimeters is convincing evidence that
particles of about the same size are present," said co-research Mark Claussen of the National Radio Astronomy Observatory.
"No one has seen this before."
One project completed?
One giant
planet may already have formed.
A computer
simulation of the disk of material around the star, based on previous infrared
observations, reveals a gap that extends from the star out to a distance of
about 400 million miles -- similar to the distance to the asteroid belt in our
solar system. The gap likely formed when a giant planet sucked up all the
nearby material, leaving a hole in the middle of
the disk, the astronomers say.
Located about
180 light-years away in the constellation Hydra the Water Snake, TW Hydrae is
nearly as massive as our Sun.
"TW
Hydrae is unique," Wilner said. "It's
nearby, and it's just the right age to be forming planets. We'll be studying it
for decades to come."
This results were detailed June 20 in Astrophysical
Journal Letters.
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