Race on for biggest earth telescope

By Robin McKie

It is hoped the new super-telescopes will be able to spot earth-like planets, asteroids and meteorites. Photo / NASA
It is hoped the new super-telescopes will be able to spot earth-like planets, asteroids and meteorites. Photo / NASA

Astronomers are taking part in a new space race - to build the world's largest telescope.

Four rival projects are under way and a series of giant observatories should be working on mountaintops in Hawaii and Chile by the end of the new decade.

Each telescope will be at least 10 times more powerful than any operating on earth today and will revolutionise our knowledge of the universe by peering further and further back into cosmos.

Among the objects that astronomers hope to study will be the first stars and galaxies that formed after the Big Bang - the birth of the universe 13.7 billion years ago.

It is also hoped the new super-telescopes will be able to spot earth-like planets in orbit round other stars and give early warnings of asteroids or meteorites heading our way.

Each instrument is scheduled for construction by around 2018. However, precise completion dates are being kept secret by each construction team.

"Being first matters," says Gary Sanders, a designer on one of the super-telescopes. "When you open a window, the first to look through it sees the most exciting things."

Sanders' observatory project is known as the Thirty Metre Telescope or TMT.

The number refers to the effective diameter of the telescope's mirror and is a measure of its light-gathering power. By contrast, the Keck Observatory - which is the world's most powerful at present - has two telescopes, each with a mirror that has a diameter of 10m.

Constructing a giant telescope is difficult, however, because a 30m mirror made of normal reflecting material starts to bend and distort under its own weight. The TMT designers believe they can get round this problem by creating a mirror that is made up of 492 small hexagonal segments.

The TMT will be built on Mauna Kea, in Hawaii. In the middle of the Pacific Ocean, the mountain is surrounded by thousands of kilometres of thermally stable seas. In addition, the 4000m summit has no nearby mountain ranges to disturb the upper atmosphere. Few city lights pollute Hawaiian night skies, and for most of the year, the atmosphere above the mountain is clear, calm and dry. Hence its popularity with astronomers, who have already built several telescopes there, including the Keck Observatory.

By contrast, the other three super-telescopes will be built in the mountains of Chile, which also benefit from having clear and calm atmospheric conditions. The Large Synoptic Survey Telescope (LSST) will use a complex system of mirrors to create what will, in effect, be a super digital camera that will be able to build up a full-colour image of the entire visible sky over a few nights. This star map will be made available to the public via Google.

Then there is the Giant Magellan Telescope (GMT), which will have seven separate mirrors, each 8.4m in diameter. Six will be arranged like petals around the seventh. This configuration will have the light-gathering power of a 24.5m telescope.

And finally, the European Extremely Large Telescope (E-ELT) will have a 42m mirror constructed from 1000 hexagonal segments and should be able to gather 15 times as much light as the Keck. It will not only be able to track down earth-like planets round other stars but detect whether they have oceans and continents.

These telescopes all exploit state-of-the-art technology: wafer-thin reflecting materials for their mirrors and highly sophisticated guidance systems. Each is likely to cost US$1 billion ($1.3 billion) but that is cheap compared with the next space telescope. Nasa's James Webb Space Telescope, which has 6.5m mirror and is set for launch in 2014, will cost US$7 billion.

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