ESO Approves 'Extremely Large Telescope' Study

The ESO Council, the governing body of the Garching-based European Southern Observatory (ESO), has authorized detailed studies for the European Extremely Large Telescope. The 57 million euro (approximately $75.4 million) studies will make it possible to start construction in three years on the optical/infrared telescope that officials said will revolutionize ground-based astronomy.

"The decision by the ESO Council to go ahead with the design study for a European Extremely Large Telescope is a very exciting one for European astronomy," said Richard Wade, president of the ESO Council.

An artist's impression of the European Extremely Large Telescope provides a bird's-eye view of the structure, which features a 42-m diameter primary mirror -- its total rotating mass is 5500 tons -- and two platforms on each side of the structure to hold large instruments. The telescope's novel design is based on five mirrors and results in exceptional image quality with no significant aberrations in the field of view. To gauge the size of the telescope, note the two people and the car in the bottom left-hand corner of the image. (Image: ESO)

Extremely Large Telescopes are considered worldwide as one of the highest priorities in ground-based astronomy. They will vastly advance astrophysical knowledge, allowing detailed studies of subjects including planets around other stars, the first objects in the Universe, supermassive black holes, and the nature and distribution of the dark matter and dark energy which dominate the Universe.

The ESO Council represents 11 European countries (Belgium, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Sweden, Switzerland and the United Kingdom; Spain is expected to become a full member before the end of 2006), accounting for most of the astronomical investment capabilities of Europe. Since the end of last year, ESO has been working with its user community of more than 100 European astronomers and astrophysicists to define the new giant telescope needed by the middle of the next decade, taking into account performance, cost, schedule and risk.

The project has moved quickly thanks to early conceptual studies done in Europe and research and development done in collaboration with a large number of European institutes and high-tech industries, officials said.

Provisionally dubbed E-ELT for the European Extremely Large Telescope, ESO's concept was presented in detail two weeks ago to more than 250 European astronomers at a conference in Marseille, France. Their enthusiastic response to the project, officials said, paved the way for the decision by the ESO Council to move to the crucial next phase: detailed design of the full facility.

"At the end of the three-year Final Design Study, we will know exactly how everything is going to be built, including a detailed costing," said Catherine Cesarsky, ESO's director general. "We then hope to start construction and have it ready by 2017, when we can install instruments and use it."

The present concept, estimated to cost around 800 million euro (approximately $1 billion), features as a baseline a telescope with a 42-m diameter mirror, and is revolutionary.

"A telescope of this size could not be built without a complete rethinking of the way we make telescopes," Cesarsky said.

The primary 42-m diameter mirror is composed of 906 hexagonal segments, each 1.45 m in size, while the secondary mirror is as large as 6 m in diameter. In order to overcome the fuzziness of stellar images due to atmospheric turbulence, the telescope needs to incorporate adaptive mirrors into its optics. Post-focal adaptive optics, i.e. optics built into the instruments and not in the telescope design itself, is a technology present in seven adaptive optics (AO) systems and a laser guide star in operation at the ESO's Very Large Telescope (VLT) at the Paranal Observatory in Atacama, Chile. VLT is currently the world's largest and most advanced optical telescope, consisting of four 8.2-m reflecting unit telescopes and several moving 1.8-m auxiliary telescopes. The VLT produces extremely sharp images and can record light from the faintest and most remote objects in the Universe.

A tertiary mirror, 4.2 m in diameter, relays the light to the AO system, composed of two mirrors: a 2.5-m mirror supported by 5000 or more actuators able to distort its own shape a thousand times per second, and one 2.7 m in diameter that allows for the final image corrections. This five-mirror approach results in an exceptional image quality, with no significant aberrations in the field of view.

With a diameter of 42-m and its AO concept, the E-ELT will be more than 100 times more sensitive than the present-day largest optical telescopes, such as the 10-m Keck telescopes or the 8.2-m VLT telescopes.

"This is really the beginning of a new era for optical and infrared astronomy," Cesarsky said.

The site of the E-ELT has not been determined; officials expect to make a decision by 2008.

For more information, visit: www.eso.org