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Last Updated: Sunday, 10 April, 2005, 09:10 GMT 10:10 UK
Ground telescopes to 'super-size'
By Paul Rincon
BBC News Science reporter, in Birmingham

Owl telescope concept (Eso)
Controlling mirrors so big is technically very challenging
A new generation of ground-based telescopes could be up to 10 times the size of existing instruments and have vision 40 times as sharp as the Hubble space telescope.

Astronomers have been hailing the plans, as a European project to build an Extremely Large Telescope (ELT) enters a design testing phase.

An ELT is vital if the pace of astronomical breakthroughs is to continue, say experts.

The plans were outlined at the UK National Astronomy Meeting in Birmingham.

Concepts for ELTs include the Thirty Meter Telescope (TMT) being considered by the US and Canada; and the Euro50 and Overwhelmingly Large Telescope (Owl) proposals put forward by Europe. The size of any European telescope has not yet been set.

But the European Southern Observatory's Owl concept could be by far the largest telescope ever built, with a spherical primary mirror that could stretch up to 100m across.

The diameter of a telescope is its key performance characteristic, because larger mirrors collect more light to concentrate in images.

ELTs would incorporate adaptive optics, a computer controlled system that deforms the mirror to adjust for the atmospheric turbulence that distorts light waves coming into the telescope.

Detecting life

One of the most exciting areas in which ELTs are certain to have a major impact is the search for Earth-like planets and by extension extra-terrestrial life.

Astronomers have already detected about 150 planets orbiting other stars using indirect methods, such as the so called "wobble effect" in which the presence of the target world is inferred from the gravitational influence it has on its parent star.

More recently, groups have released images which they claim show distant worlds in other Solar Systems directly. Many astronomers are unconvinced - but, even so, all of these exoplanets so far detected are unlikely to be much like our own.

What all these projects have in common is that you can't build a mirror bigger than about 8m across in one piece
Dr Isobel Hook, ELT
"The candidate exoplanets which we have images for are probably going to be young, giant planets which are nothing like what we have in the Solar System," said Dr Isobel Hook, an ELT project scientist from the University of Oxford, UK.

"If you want to be able to study a mature planet which is not emitting its own light anymore, you need to cope with a much larger contrast between the bright star and the faint planet.

"For that, you need a much bigger telescope," she told the BBC News website.

Multi-part mirrors

ELTs could study the chemical composition of Earth-like planets, detecting the presence of liquid water, oxygen or methane.

Telescopes this powerful might even be able to detect vegetation on a distant planet, by looking at a characteristic spectral signature from chlorophyll, the key pigment involved in photosynthesis.

The "quantum leap" in performance possible with ELTs will also help astronomers gain a better understanding of galaxies and when their stars formed, and answer the many outstanding questions about the nature of mysterious dark matter and dark energy - which forms 95% of the known Universe.

Euro50 concept (Euro50)
The scale of the projects means they have to be collaborative
But building these gargantuan observatories poses significant technical challenges.

"What all these projects have in common is that you can't build a mirror bigger than about 8m across in one piece," said Dr Hook.

"If you want to make something bigger than that, you have to make it from smaller pieces."

Some ELT designs involve combining several circular 8m-wide mirrors. But others, like the Owl and the Euro-50, will have mirrors constructed from many small hexagonal segments.

The Owl design uses a spherical, rather than the usual parabolic, mirror shape to cut down on cost. This means its segments can be the same shape and size and can be mass-produced.

But this also means the telescope's field does not have a focus, so the Owl requires several corrective mirrors.

The Owl concept works for a telescope of around 100m, but below the 60m mark, the Euro-50 design - with its smaller parabolic mirror - may strike a better deal between cost and performance.

The design study which is currently underway will determine which of these concepts Europe should go with.

The Royal Astronomical Society's National Astronomy Meeting has been held at the University of Birmingham.

Astronomers expect to be 'Dazled'
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04 Apr 05 |  Science/Nature
Astronomers plan giant telescope
22 Oct 03 |  Science/Nature
Europe plans world's biggest telescope
05 Dec 02 |  Science/Nature
Astronomy's next big thing
08 Jul 02 |  Science/Nature

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