| European Extremely Large Telescope (E-ELT) | |
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An artist's impression of the E-ELT
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| Organization | ESO |
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| Location | Cerro Armazones, Chile, near Paranal Observatory |
| Altitude | 3060 m[1] |
| Weather | Good |
| Wavelength | Optical, near infrared |
| Built | Planned completion: 2022 first light[2] |
| Telescope style | Reflector |
| Diameter | 39.3m |
| Angular resolution | 0.001 to 0.65 arcseconds depending on target and instruments used |
| Collecting area | 978 m2 |
| Focal length | 420–840 m (f/10 – f/20) |
| Mounting | Nasmyth mount |
| Website | ESO E-ELT |
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.[2] 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.[2]
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."[3] The ESO Council endorsed the revised baseline design in June 2011 and expects a construction proposal for approval in December 2011.[3]
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.[4] The main mirror will be made up from almost 800 hexagonal segments.[5] If completed it may be the largest of a new generation of extremely large telescopes.[2]
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.[6]
On 26 April 2010, the European Southern Observatory (ESO) Council selected Cerro Armazones, Chile, as the baseline site for the planned E-ELT.[7] 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.[8]
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The ESO is focusing on the current design after a feasibility study concluded the proposed 100 metres (330 ft) diameter Overwhelmingly Large Telescope 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.[4]
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 planets.[9] 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.[10] 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.”[11]
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.[12] The telescope main structure will weigh about 2800 tons.[13]
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.[14]
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.[5]
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?[6]
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.[5]
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.[15]
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.[15]
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.[16] The instruments being studied are:
The two post-focal adaptive optics modules currently being studied are:
The largest ground-based telescope operating today is the Gran Telescopio Canarias, with a 10.4m aperture and a light-collecting area of 74m2. Other planned extremely large telescopes 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.[20][21] Each design is much larger than previous telescopes.[2] 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.
The images below show artistic renderings of the E-ELT and were produced by ESO.
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