ASTRONOMERS in Britain have earned a place in history by making
the first direct sighting of a planet orbiting another sun. The
new world, which has been called the "millennium planet'',
is 55 light-years from earth, nearly twice the size of Jupiter and
probably blue in colour with high clouds, they report.
Sophisticated computer software was used to untangle the planet's
light from the glare of its parent star, Tau Bootis, which is 30,000
times brighter. As a result the astronomers were able to "see''
the planet, or at least detect its reflected light. No-one has ever
achieved this before. Until now almost every other known extra-solar
planet has been detected indirectly by measuring the "wobble''
its gravity imparts on the star it orbits.
In the past four years, 28 nearby sun-like stars, including Tau
Bootis, have been assumed to possess planets by this method. In
November, two teams in the United States detected the "shadow''
of one of these planets. They saw a brief dimming in the light of
the star HD 209458 as the planet crossed its face. But although
the observation was a major step forward it pales next to the UK
scientists' achievement: the first extra-solar planet discovery
made by UK astronomers.
Capturing light from the surface of the planet provides scientists
with a potential goldmine of information. For the first time it
is possible to say something meaningful about the composition of
a planet in another solar system.
The astronomers know the millennium planet is about 1.8 times
the diameter of Jupiter but eight times its mass, orbiting close
to the star and very hot with a surface temperature of around 1,100
degrees Celsius. They can also assume that the planet is bluish
in colour and with a cloudy atmosphere. Despite being a gas giant
with no solid core it would probably contain solid particles. The
planet is thought to be composed mainly of heated hydrogen but its
blue colour suggests the presence of magnesium, possibly in the
form of silicate droplets.
Further detailed analysis of the planet's faint light spectrum
is expected to reveal more precisely of what it is made.
One of the astronomers, Dr Alan Penny, from the Rutherford Appleton
Laboratory in Didcot, Oxfordshire, southern England, said: ``For
the first time it has been possible to capture light from an extra-solar
planet and use it to make some sense of the planet's physical constituents.
Our discovery is a major step in finding out what these planets
are really like, a step that could lead to finding planets like
Dr Penny is one of the chief scientists behind the Darwin mission,
a European plan to launch a giant space telescope in 2012 specifically
designed to search for earth-like life-sustaining planets in other
solar systems. But he doubted there was life on the millennium planet.
''There probably won't be any life there,'' he said. ``This is
a gas giant, like Jupiter. It's too hot and has no solid surface
and no liquid water. You can speculate but if there were any life
it wouldn't be life as we know it.''
The astronomers made the discovery with the 4.2-metre William
Herschel telescope on La Palma in the Canary Islands. A first attempt
in 1998 produced no clear sign of the planet. But computer analysis
revealed a faint copy of the star's spectrum embedded in the starlight
from Tau Bootis.
The faint light signal wobbled back and forth in the opposite
direction to the star's own smaller wobble. This told the astronomers
they were picking up light reflected from the surface of a closely
orbiting planet tilted to the line of sight.
- Next news