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Exoplanets finally come into view
The first pictures of planets outside our solar system have been taken, two
groups report in the journal Science.
Visible and infrared images have been snapped of a planet orbiting a star 25
The planet is believed to be the coolest, lowest-mass object ever seen outside
our own solar neighbourhood.
In a separate study, an exoplanetary system comprising three planets has been
directly imaged, circling a star in the constellation Pegasus.
While several claims have been made to such direct detection before, they have
later been proven wrong.
It's a profound and overwhelming experience to lay eyes on a planet never
Paul Kalas, University of California
The search for exoplanets has up to now depended on detecting either the wobble
they induce on their parent star or, if their orbits are side-on to telescopes,
watching them dim the star's light as they pass in front of it.
Being able to directly detect the light from these planets will allow
astronomers to study their composition and atmospheres in detail.
The difficulty for astronomers imaging exoplanets has until now been that their
parent stars' light swamps them - like trying to spot a match next to a
floodlight at a distance of a mile.
But advances in optics and image processing have allowed astronomers to
effectively subtract the bright light from stars, leaving behind light from the
planets. That light can either come in the infrared, caused by the planets'
heat, or be reflected starlight.
Paul Kalas of the University of California led an international group that used
the Hubble Space Telescope to image the region around a star called Fomalhaut.
The star has a massive ring of dust surrounding it that appears to have a
cleanly groomed inner edge.
That is in keeping with what is known as accretion theory - that young planets
gather up dust and matter as they orbit - and prompted the team to begin
looking for the suspected planet in 2005.
The team estimates that the planet, dubbed Fomalhaut b, is 11bn miles away from
its star, about as massive as Jupiter and completes an orbit in about 870
years. It may also have a ring around it.
"I nearly had a heart attack at the end of May when I confirmed that Fomalhaut
b orbits its parent star," Dr Kalas said. "It's a profound and overwhelming
experience to lay eyes on a planet never before seen."
Christian Marois of the Herzberg Institute for Astrophysics and his team used
the Keck and Gemini telescopes in Hawaii to look near a star called HR 8799,
which is just visible to the naked eye.
The team looked for light in the infrared part of the spectrum, hoping to spot
planets that were still hot from their formation.
What they found in 2004, and confirmed again this year, are three planets
circling the star.
According to a theoretical model that accounts for the light coming from the
planets, they range in size from five to 13 times the mass of Jupiter and are
probably only about 60 million years old.
The trio have similarities with our own solar system. Their orbits are
comparable in size to those of the outer planets, and the smaller planets are
those closest to the sun - again suggesting a system that formed through
Dr Marois points out that the current methods used in the exoplanet hunt are
sensitive primarily to Jupiter-sized planets and larger.
"We thus do not have a full picture," he told BBC News. "The detection of the
three planets around HR 8799 does not mean that no planets are orbiting at
smaller separations. Other gas giant or even rocky planets could reside there."
Believing the seeing
The study of the light directly from the planets will yield information about
their atmospheres and surfaces that is impossible to collect from planets
Further, the current results will also support theories of how planets form
from the grand discs of dust and material around stars, and lead to better
estimates of how many Earth-like planets are likely to exist.
These latest claims are both based on observations that were well-spaced in
time, allowing the researchers to apply a rigorous test for direct detection.
"You see an object next to a star and you might think it's a planet," Mark
McCaughrean, an astrophysicist at the University of Exeter, told BBC News.
"But you have to watch it for several years and make sure that it moves around
the star and with the star as it moves across the sky. Though I've been very
sceptical in the past, these ones all seem pretty real to me.
"It's like a London bus - you've been waiting for one for ages and suddenly
four come along at once."
Story from BBC NEWS:
Published: 2008/11/13 19:00:27 GMT
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