|
By Will Dunham
WASHINGTON
(Reuters) - Astronomers have peered inside a stellar nursery for young planets
in the Orion Nebula, but what they saw looked more like a bar-room brawl than
a day-care center.
Glimpsing the first stages of planet formation, astronomers
said on Thursday they used observations from NASA's Hubble Space Telescope to
confirm that tiny particles orbiting in million-year-old dusty disks surrounding
several young sun-like stars in the Orion Nebula are clumping together and growing.
The
colossal nebula is located 1,500 light-years from Earth and represents the nearest,
large-scale ``star-factory'' to our solar system.
But researchers led by
John Bally of the University of Colorado in Boulder and Henry Throop of the Southwest
Research Institute in Boulder said most of the tiny, fledgling planets were evaporated
by a blistering flood of radiation from the nebula's brightest star, called Theta
1 Orionis C.
The findings, appearing in the journal Science, mark the first
direct visual evidence of the growth of planet ``building blocks'' inside dust
disks forming around young stars.
``It's remarkable that we're actually
seeing the first phases of this process (of planet formation) happening in front
of our eyes,'' Bally said in an interview.
The astronomers said the Hubble
data indicates that it may be easy to start building planets but finishing the
job is a bit more tricky. Astronomers theorize that some dust particles will stick
together like a snowball picking up snow as it rolls along the ground until they
become the size of planets.
But Orion's hostile environment is seen as
typical of star-forming regions across the Milky Way galaxy, home to our solar
system. Earth, the eight other planets and numerous moons and other objects formed
around the Sun 4.5 billion years ago.
Building A Skyscraper In A Tornado
Throop
said the findings mark the first time that large, growing grains, which range
in size from smoke particles to sand grains, have been seen in visible light in
``protoplanetary disks.''
``We have two things happening in these systems:
dust grains are beginning to stick together as a first step toward making planets,
but then these bright stars are trying to tear everything apart. Which one wins
is really a big question. It's like trying to build a skyscraper in the middle
of a tornado,'' Throop said.
Depending on whether or not they can form
quickly before being obliterated, planets may be rarer in the Milky Way than previously
thought, the researchers said. That equation could affect the potential prevalence
of life in the universe.
``Planets are the abodes of life. There's no other
place, as far as I know,'' Bally said. Bally said 10 percent of stars may have
planets orbiting around them.
Bally said that in active star nurseries
like Orion, large and powerful type O or type B stars make planetary formation
around smaller, sun-like stars difficult. He said ultraviolet light comes streaming
off the large stars like a blowtorch, evaporating the gases and removing the dust
from the dust rings around the smaller stars that could give rise to planets.
Bally
said so-called rocky planets like Earth may be able to form in Orion, but doubted
whether giant gaseous planets like Jupiter and Saturn could survive the birthing
process.
Hubble was used to look at the dust rings surrounding stars in
Orion in the visible and near-infrared wavelengths of light. The background light
from the Orion Nebula bounces off dust particles, scattering the light in a way
that allowed astronomers to gauge the size of the particles. |
