Extremely Large Telescope
Encyclopedia
The European Extremely Large Telescope (E-ELT) is a ground-based extremely large telescope
featuring an optical/near-infrared telescope of large size and advanced features that is being planned by the European Southern Observatory
(ESO). Planned features until 2011 included a filled single aperture mirror with a diameter of 42 metres and area of about 1300 m2, with a secondary mirror with a diameter of 5.9 m. However, in 2011 a proposal was put forward to reduce its size by 13% to 978 m2, for a 39.3 m diameter primary mirror and a 4.2 m diameter secondary mirror. This reduces the projected costs from 1275M to 1055M euros and should allow the telescope to be finished sooner. However, it will likely make it harder for the telescope to image Earthlike exoplanets, though that goal is still possible.
ESO's Director General commented in a press release that "With the new E-ELT design we can still satisfy the bold science goals and also ensure that the construction can be completed in only 10-11 years." The ESO Council endorsed the revised baseline design in June 2011 and expects a construction proposal for approval in December 2011.
The telescope's "eye" will be almost half the length of a football pitch (soccer field) in diameter and will gather 15 times more light than the largest optical telescopes operating today. The telescope has an innovative five-mirror design that includes advanced adaptive optics to correct for the turbulent atmosphere, giving exceptional image quality. The main mirror will be made up from almost 1000 hexagonal segments. If completed it may be the largest of a new generation of extremely large telescope
s.
The E-ELT is a frontline scientific project that will further expand Europe's leading role in astronomy and allow people to address many of the most pressing unsolved questions about the Universe. It will allow astronomers to probe the earliest stages of the formation of planetary systems and to detect water and organic molecules in proto-planetary discs around stars in the making. In other words, it is the first telescope that could enable us to identify life beyond the Solar System.
On 26 April 2010, the European Southern Observatory
(ESO) Council selected Cerro Armazones
, Chile
, as the baseline site for the planned E-ELT. Other sites that were under discussion included Cerro Macon, Salta, in Argentina; Roque de los Muchachos Observatory, on the Canary Islands; and sites in South Africa, Morocco, and Antarctica.
would cost €1.5 billion (£1 billion), and be too complex. Current fabrication technology limits single mirrors to being roughly 8 metres (26 ft) in a single piece. The next-largest telescopes currently in use are the Gran Telescopio Canarias
and Southern African Large Telescope
, which each use hexagonal mirrors fitted together to make a mirror more than 10 metres (33 ft) across. The E-ELT will use a similar design, as well as techniques to work around atmospheric distortion of incoming light, known as adaptive optics
.
Project E-ELT has the aim of observing the Universe in greater detail than even the Hubble Space Telescope
, providing images 15 times sharper than those of this observatory although it is designed to be complimentary to space telescopes which have very limited time available. A 40m-class mirror will allow the study of the atmospheres of extrasolar planet
s. The E-ELT is the highest priority in the European planning activities for research infrastructures, such as the Astronet
Science Vision and Infrastructure Roadmap and the ESFRI Roadmap. The telescope underwent a Phase B study in the past couple of years that included "contracts with industry to design and manufacture prototypes of key elements like the primary mirror segments, the adaptive fourth mirror or the mechanical structure (...) [and] concept studies for eight instruments.”
The primary mirror for the 39.3 metre design will be composed of 798 hexagonal segments, each 1.45 meters across but only 50 mm thick. A special correcting mirror in the telescope will be supported by more than 6000 actuators that can distort its shape a thousand times per second. The telescope main structure will weigh about 2800 tons.
The E-ELT will complete its detailed-design phase by the end of 2011 and its construction is planned for 2012. The design phase of the 5-mirror anastigmat
is fully funded within the ESO budget. With the recent changes in the baseline design (such as a reduction in the size of the primary mirror from 42m to 39.3m), the construction cost is estimated to be €1055M (including first generation instruments). The start of operations is planned for early in the next decade.
Furthermore, the E-ELT's suite of instruments will allow astronomers to probe the earliest stages of the formation of planetary systems and to detect water and organic molecules in protoplanetary discs around stars in the making. Thus, the E-ELT will answer fundamental questions regarding planet formation and evolution and will bring us one step closer to answering the question: are we alone?
By probing the most distant objects the E-ELT will provide clues to understanding the formation of the first objects that formed: primordial stars, primordial galaxies and black holes and their relationships. Studies of extreme objects like black holes will benefit from the power of the E-ELT to gain more insight into time-dependent phenomena linked with the various processes at play around compact objects.
The E-ELT is designed to make detailed studies of the first galaxies and to follow their evolution through cosmic time. Observations of these early galaxies with the E-ELT will give clues that will help understand how these objects form and evolve. In addition, the E-ELT will be a unique tool for making an inventory of the changing content of the various elements in the Universe with time, and to understand star formation history in galaxies.
One of the most exciting goals of the E-ELT is the possibility of making a direct measurement of the acceleration of the Universe's expansion. Such a measurement would have a major impact on our understanding of the Universe. The E-ELT will also search for possible variations in the fundamental physical constants with time. An unambiguous detection of such variations would have far-reaching consequences for our comprehension of the general laws of physics.
Eight different instrument concepts and two post-focal adaptive modules are currently being studied, with the aim that two to three will be ready for first light, with the others becoming available at various points over the following decade. The instruments being studied are:
The two post-focal adaptive optics modules currently being studied are:
, with a 10.4m aperture and a light-collecting area of 74m2. Other planned extremely large telescope
s include, the 25 m/368 m2 Giant Magellan Telescope
and 30 m/655 m2 Thirty Meter Telescope
, which are also targeting the end of this decade or beginning of the next for completion. These other two telescopes roughly belong to the same next generation of optical ground-based telescopes. Each design is much larger than previous telescopes. Even with the descale of the E-ELT, the telescope is significantly larger than these other planned observatories, with a diameter of the primary mirror at 39.3 m and a light-collecting area of 1116 m2.
Extremely large telescope
An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
featuring an optical/near-infrared telescope of large size and advanced features that is being planned by the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
(ESO). Planned features until 2011 included a filled single aperture mirror with a diameter of 42 metres and area of about 1300 m2, with a secondary mirror with a diameter of 5.9 m. However, in 2011 a proposal was put forward to reduce its size by 13% to 978 m2, for a 39.3 m diameter primary mirror and a 4.2 m diameter secondary mirror. This reduces the projected costs from 1275M to 1055M euros and should allow the telescope to be finished sooner. However, it will likely make it harder for the telescope to image Earthlike exoplanets, though that goal is still possible.
ESO's Director General commented in a press release that "With the new E-ELT design we can still satisfy the bold science goals and also ensure that the construction can be completed in only 10-11 years." The ESO Council endorsed the revised baseline design in June 2011 and expects a construction proposal for approval in December 2011.
The telescope's "eye" will be almost half the length of a football pitch (soccer field) in diameter and will gather 15 times more light than the largest optical telescopes operating today. The telescope has an innovative five-mirror design that includes advanced adaptive optics to correct for the turbulent atmosphere, giving exceptional image quality. The main mirror will be made up from almost 1000 hexagonal segments. If completed it may be the largest of a new generation of extremely large telescope
Extremely large telescope
An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
s.
The E-ELT is a frontline scientific project that will further expand Europe's leading role in astronomy and allow people to address many of the most pressing unsolved questions about the Universe. It will allow astronomers to probe the earliest stages of the formation of planetary systems and to detect water and organic molecules in proto-planetary discs around stars in the making. In other words, it is the first telescope that could enable us to identify life beyond the Solar System.
On 26 April 2010, the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
(ESO) Council selected Cerro Armazones
Cerro Armazones
Cerro Armazones is a mountain located in the Sierra Vicuña Mackenna of the Chilean Coast Range, approximately 130 km south-east of Antofagasta in the Antofagasta Region, Chile. It has a height of 3,064 m and is located in a privileged zone for optical astronomy since it receives almost 350...
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, as the baseline site for the planned E-ELT. Other sites that were under discussion included Cerro Macon, Salta, in Argentina; Roque de los Muchachos Observatory, on the Canary Islands; and sites in South Africa, Morocco, and Antarctica.
Goals and planning
The ESO is focusing on the current design after a feasibility study concluded the proposed 100 metres (328.1 ft) diameter Overwhelmingly Large TelescopeOverwhelmingly Large Telescope
The Overwhelmingly Large Telescope is a conceptual design by the European Southern Observatory organization for an extremely large telescope, which was intended to have a single aperture of 100 meters in diameter...
would cost €1.5 billion (£1 billion), and be too complex. Current fabrication technology limits single mirrors to being roughly 8 metres (26 ft) in a single piece. The next-largest telescopes currently in use are the Gran Telescopio Canarias
Gran Telescopio Canarias
The Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
and Southern African Large Telescope
Southern African Large Telescope
The Southern African Large Telescope is a 66m2 area optical telescope with a nominally 9.2 meter aperture but up to about 11.1m x ~9.8 m diameter aperture, and designed mainly for spectroscopy. It is located close to the town of Sutherland in the semi-desert region of the Karoo, South Africa...
, which each use hexagonal mirrors fitted together to make a mirror more than 10 metres (33 ft) across. The E-ELT will use a similar design, as well as techniques to work around atmospheric distortion of incoming light, known as adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
.
Project E-ELT has the aim of observing the Universe in greater detail than even the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
, providing images 15 times sharper than those of this observatory although it is designed to be complimentary to space telescopes which have very limited time available. A 40m-class mirror will allow the study of the atmospheres of extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
s. The E-ELT is the highest priority in the European planning activities for research infrastructures, such as the Astronet
Astronet
Starting September 2005, 1st, Astronet is a consortium which gather European funding agencies in order to «establish a comprehensive long-term planning for the development of European astronomy»- Participants :*CNRS/INSU , France,...
Science Vision and Infrastructure Roadmap and the ESFRI Roadmap. The telescope underwent a Phase B study in the past couple of years that included "contracts with industry to design and manufacture prototypes of key elements like the primary mirror segments, the adaptive fourth mirror or the mechanical structure (...) [and] concept studies for eight instruments.”
The primary mirror for the 39.3 metre design will be composed of 798 hexagonal segments, each 1.45 meters across but only 50 mm thick. A special correcting mirror in the telescope will be supported by more than 6000 actuators that can distort its shape a thousand times per second. The telescope main structure will weigh about 2800 tons.
The E-ELT will complete its detailed-design phase by the end of 2011 and its construction is planned for 2012. The design phase of the 5-mirror anastigmat
Anastigmat
An Anastigmat or anastigmatic lens is a photographic lens completely corrected for spherical aberration, coma, and astigmatism. Early lenses often included the word Anastigmat in their name to advertise this new feature...
is fully funded within the ESO budget. With the recent changes in the baseline design (such as a reduction in the size of the primary mirror from 42m to 39.3m), the construction cost is estimated to be €1055M (including first generation instruments). The start of operations is planned for early in the next decade.
Science goals
The E-ELT has embraced the quest for extrasolar planets — planets orbiting other stars. This will include not only the discovery of planets down to Earth-like masses through indirect measurements of the wobbling motion of stars perturbed by the planets that orbit them, but also the direct imaging of larger planets and possibly even the characterisation of their atmospheres.Furthermore, the E-ELT's suite of instruments will allow astronomers to probe the earliest stages of the formation of planetary systems and to detect water and organic molecules in protoplanetary discs around stars in the making. Thus, the E-ELT will answer fundamental questions regarding planet formation and evolution and will bring us one step closer to answering the question: are we alone?
By probing the most distant objects the E-ELT will provide clues to understanding the formation of the first objects that formed: primordial stars, primordial galaxies and black holes and their relationships. Studies of extreme objects like black holes will benefit from the power of the E-ELT to gain more insight into time-dependent phenomena linked with the various processes at play around compact objects.
The E-ELT is designed to make detailed studies of the first galaxies and to follow their evolution through cosmic time. Observations of these early galaxies with the E-ELT will give clues that will help understand how these objects form and evolve. In addition, the E-ELT will be a unique tool for making an inventory of the changing content of the various elements in the Universe with time, and to understand star formation history in galaxies.
One of the most exciting goals of the E-ELT is the possibility of making a direct measurement of the acceleration of the Universe's expansion. Such a measurement would have a major impact on our understanding of the Universe. The E-ELT will also search for possible variations in the fundamental physical constants with time. An unambiguous detection of such variations would have far-reaching consequences for our comprehension of the general laws of physics.
Instrumentation
The telescope will have several science instruments. It will be possible to switch from one instrument to another within minutes. The telescope and dome will also be able to change positions on the sky and start a new observation in a very short time.Eight different instrument concepts and two post-focal adaptive modules are currently being studied, with the aim that two to three will be ready for first light, with the others becoming available at various points over the following decade. The instruments being studied are:
- CODEX: a very high resolution optical spectrographSpectrographA spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
- EAGLE: a wide-field, multiple integral field unit near-infrared (NIR) spectrograph, with multi-object adaptive optics
- EPICS: a optical/NIR planet imager and spectrograph with extreme adaptive optics
- HARMONI: a single field, wide-band spectrograph
- METIS: a mid-infrared imager and spectrograph
- MICADO: a diffraction-limited near-infrared camera
- OPTIMOS: a wide-field visual multi-object spectrograph
- SIMPLE: a high spectral resolution NIR spectrograph
The two post-focal adaptive optics modules currently being studied are:
- ATLAS: a laser tomography adaptive optics module
- MAORY: a multi-conjugate adaptive optics module
Comparison
The largest ground-based telescope operating today is the Gran Telescopio CanariasGran Telescopio Canarias
The Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
, with a 10.4m aperture and a light-collecting area of 74m2. Other planned extremely large telescope
Extremely large telescope
An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
s include, the 25 m/368 m2 Giant Magellan Telescope
Giant Magellan Telescope
The Giant Magellan Telescope is a ground-based extremely large telescope planned for completion in 2018. It will consist of seven diameter primary segments, with the resolving power of a primary mirror and collecting area equivalent to one...
and 30 m/655 m2 Thirty Meter Telescope
Thirty meter telescope
The Thirty Metre Telescope is a proposed ground-based large segmented mirror reflecting telescope to be built on Mauna Kea in Hawaii. The telescope is designed for observations from the near-ultraviolet to the mid-infrared . An adaptive optics system would correct for image blur caused by the...
, which are also targeting the end of this decade or beginning of the next for completion. These other two telescopes roughly belong to the same next generation of optical ground-based telescopes. Each design is much larger than previous telescopes. Even with the descale of the E-ELT, the telescope is significantly larger than these other planned observatories, with a diameter of the primary mirror at 39.3 m and a light-collecting area of 1116 m2.
Competition
- Thirty Meter TelescopeThirty meter telescopeThe Thirty Metre Telescope is a proposed ground-based large segmented mirror reflecting telescope to be built on Mauna Kea in Hawaii. The telescope is designed for observations from the near-ultraviolet to the mid-infrared . An adaptive optics system would correct for image blur caused by the...
(plan) - Giant Magellan TelescopeGiant Magellan TelescopeThe Giant Magellan Telescope is a ground-based extremely large telescope planned for completion in 2018. It will consist of seven diameter primary segments, with the resolving power of a primary mirror and collecting area equivalent to one...
(plan) - Overwhelmingly Large TelescopeOverwhelmingly Large TelescopeThe Overwhelmingly Large Telescope is a conceptual design by the European Southern Observatory organization for an extremely large telescope, which was intended to have a single aperture of 100 meters in diameter...
(retired plan)
Gallery
The images below show artistic renderings of the E-ELT and were produced by ESO.See also
- List of largest optical reflecting telescopes
- Large Binocular TelescopeLarge Binocular TelescopeLarge Binocular Telescope is an optical telescope for astronomy located on Mount Graham in the Pinaleno Mountains of southeastern Arizona, and is a part of the Mount Graham International Observatory...
(11.8 m2, 2 aperture) - Gran Telescopio CanariasGran Telescopio CanariasThe Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
(10.4 m 2, 1 aperture)