Extremely Large Telescope

Extremely Large Telescope
Name	Extremely Large Telescope
Organization	European Southern Observatory
Location	Cerro Armazones, Atacama Desert, Chile
Wavelength	Optical, near-infrared
Built	2017–present (expected completion 2028)
First light	2028 (planned)
Diameter	39.3 m (primary mirror)
Collecting area	978 m²

Extremely Large Telescope. The Extremely Large Telescope is a revolutionary ground-based astronomical observatory currently under construction by the European Southern Observatory in the Atacama Desert of northern Chile. Upon completion around 2028, it will be the world's largest optical and near-infrared telescope, featuring an unprecedented 39.3-meter primary mirror composed of 798 individual segments. This colossal instrument is designed to address some of the most profound questions in modern astronomy, from characterizing exoplanet atmospheres to observing the first galaxies in the early universe.

Overview

The project represents the culmination of decades of technological advancement in adaptive optics and large-telescope design pioneered by institutions like the European Southern Observatory with its earlier Very Large Telescope. Funded by ESO's member states, which include many European countries and host nation Chile, the telescope is a flagship endeavor for the global astronomical community. Its development follows in the lineage of other giant telescopes, such as the Thirty Meter Telescope and the Giant Magellan Telescope, but will surpass them in light-collecting area. The decision to build on Cerro Armazones was made after extensive site testing, confirming the exceptional atmospheric conditions of the region.

Design and construction

The core of the design is its innovative five-mirror optical system, which includes the segmented 39.3-meter primary mirror, a 4.2-meter convex secondary mirror, and a 3.8-meter flat tertiary mirror. Two additional mirrors relay light to the adaptive optics system and the instruments. The primary mirror's 798 hexagonal segments, each 1.4 meters across and 5 cm thick, are made of Zerodur and are actively controlled by sensors and actuators to maintain a perfect parabolic shape. The massive dome, rising over 80 meters high, is a rotating structure designed to minimize thermal disturbances and wind shake. Major construction contracts have been awarded to consortia across Europe, with the structure being built by the ACe Consortium and the dome by the MT Mechatronics and ESO team.

Scientific goals and capabilities

Its primary scientific objectives are extraordinarily ambitious, leveraging its immense light-gathering power and high angular resolution. A key goal is the direct imaging and spectroscopic analysis of Earth-like exoplanets orbiting nearby stars, searching for potential biosignatures in their atmospheres. The telescope will also probe the formation and evolution of galaxies by observing some of the earliest stellar systems, dating back to the cosmic dawn just a few hundred million years after the Big Bang. Further studies will include detailed observations of black hole environments, the physics of star formation, and the nature of dark matter and dark energy by measuring the acceleration of the universe's expansion with unprecedented precision.

Instruments

A suite of first-generation instruments is being developed to exploit the telescope's capabilities. The MICADO instrument will be a high-resolution near-infrared camera and spectrograph, working with a laser-guided adaptive optics system to achieve diffraction-limited imaging. HARMONI is an integral field spectrograph covering visible and near-infrared wavelengths, designed for detailed studies of galaxies and exoplanets. The mid-infrared instrument, METIS, will conduct high-contrast imaging and spectroscopy, ideal for studying protoplanetary disks and cool exoplanets. A multi-object spectrograph, initially planned as MOSAIC, is also under consideration to survey vast fields of faint galaxies and stars.

Site and telescope characteristics

The site on Cerro Armazones, a 3,046-meter peak approximately 20 kilometers from ESO's Paranal Observatory, was selected for its superb atmospheric stability, low humidity, and high number of clear nights per year. The telescope's enclosure is engineered to ventilate naturally, keeping the internal temperature close to the ambient night air to reduce thermal turbulence. The entire structure, weighing over 5,000 tonnes, will float on a hydrostatic bearing system for exceptionally smooth rotation. The adaptive optics system, using multiple laser guide stars and a deformable mirror, will correct for atmospheric distortion in real time, allowing the telescope to approach its theoretical diffraction limit.

Timeline and status

The project was formally approved by the ESO Council in 2012, with a groundbreaking ceremony held in 2017. Major milestones include the completion of the dome and main structure, with telescope assembly inside the dome ongoing. Casting and polishing of the primary mirror segments by the German company SCHOOTT is largely complete, with coating and integration proceeding. As of 2024, construction is advanced, with first light for the telescope currently anticipated for 2028. Once operational, it will immediately become one of the most powerful tools for observational astronomy, with its observing time allocated through competitive proposals from the global scientific community.

Category:Extremely Large Telescope Category:European Southern Observatory Category:Telescopes under construction Category:Buildings and structures in Antofagasta Region