Thirty Meter Telescope
Artist's rendering of proposed telescope
|Organization||TMT International Observatory|
|Location(s)||Mauna Kea Observatory, Hawaii, United States|
|Altitude||4,050 m or 13,290 ft|
|Wavelength||Near UV, visible, and Mid-IR (0.31–28 μm)|
|First light||est. 2022|
|Telescope style||Segmented Ritchey–Chrétien telescope|
|Diameter||30 m or 98 ft|
|Secondary dia.||3.1 m or 10 ft|
|Tertiary dia.||2.5 m × 3.5 m or 8.2 ft × 11.5 ft|
|Collecting area||655 m2 or 7,050 sq ft|
|Focal length||f/15 (450 m):52|
|Related media on Wikimedia Commons|
The Thirty Meter Telescope (TMT) is an astronomical observatory with an Extremely Large Telescope (ELT) that has become the source of controversy over its planned location on Mauna Kea in the state of Hawaii.
Scientists have been considering ELTs since the mid 1980s. In 2000, astronomers considered the possibility of a telescope with a light-gathering mirror larger than 20 meters in diameter. The technology to build a mirror larger than 8.4 meters does not exist; instead scientists considered using either small segments that create one large mirror, or a grouping of larger 8-meter mirrors working as one unit. The US National Academy of Sciences recommended a 30-meter telescope be the focus of U.S. interests, seeking to see it built within the decade. Scientists at the University of California and Caltech began development of a design that would eventually become the TMT, consisting of 492 segmented mirrors with nine times the power of the Keck telescope. Due to its immense light-gathering power and the optimal observing conditions which exisit atop Mauna Kea, the TMT would enable astronomers to conduct research which is unfeasible with current instruments. The TMT is designed for near-ultraviolet to mid-infrared (0.31 to 28 μm wavelengths) observations, featuring adaptive optics to assist in correcting image blur. The TMT will be at the highest altitude of all the proposed ELTs. The telescope has government-level support from several R&D spending nations: China, Japan, Canada and India.
Construction of the ELT on land which is sacred to native Hawaiians, attracted international coverage after October of 2014, when construction was temporarily halted voluntarily due to protests. While construction of the telescope was set to resume on April 2 and later on June 24, 2015, it was blocked by further protests each time. The observatory and telescope are expected to be operational on Mauna Kea by 2024.
In 2000, astronomers began considering the potential of telescopes larger than 20 meters in diameter. Two technologies were considered; segmented mirrors like that of the Keck Observatory and the use of a group of 8-meter mirrors mounted to form a single unit. The US National Academy of Sciences made a suggestion that a 30-meter telescope should be the focus of US astronomy interests and recommended it to be built within the decade. The University of California, along with Caltech began development of a 30-meter telescope that same year. The California Extremely Large Telescope (CELT) began development along with the Giant Magellan Telescope, the Giant Segmented Mirror Telescope (GSMT) and the Very Large Optical Telescope (VLOT). These studies would eventually become the Thirty Meter Telescope. The TMT would have nine times the collecting area of the older Keck telescope using slightly smaller mirror segments in a vastly larger group. Another telescope of a large diameter in the works is the European Extremely Large Telescope (E-ELT) being built in northern Chile.
The telescope is designed for observations from near-ultraviolet to mid-infrared (0.31 to 28 μm wavelengths). In addition, its adaptive optics system will help correct for image blur caused by the atmosphere of the Earth, helping it to reach the potential of such a large mirror. Among existing and planned ELTs, the TMT will have the highest altitude and will be the second-largest telescope once the E-ELT is built. Both use segments of small 1.44 m hexagonal mirrors—a design vastly different from the large mirrors of the Large Binocular Telescope (LBT) or the Giant Magellan Telescope (GMT). The TMT has government-level support from two large R&D spending nations; China and Japan, as well as other top R&D ones, including Canada and India. The United States is also contributing some funding, but less than the formal partnership.
The telescope was given approval by the state Board of Land and Natural Resources in April 2013. The Intermediate Court of Appeals of the State of Hawaii declined to hear an appeal of the permit until the Hawaii Department of Land and Natural Resources first issued a decision from a contested case hearing that could then be appealed to the court. The dedication and ground-breaking ceremony was held, but interrupted by native Hawaiian protesters on October 7, 2014. The project has now become the focal point of escalating political conflict, police arrests, and continuing litigation due to concerns over proper use of conservation lands, continued environmental degradation and the process of environmental and cultural impact review, the status of the Hawaii ceded land trust, native Hawaiian cultural practice and religious rights, and concerns over the lack of meaningful and inclusive dialogue during the permitting process.
The TMT would be a general-purpose observatory capable of investigating a broad range of astrophysical problems. Total diameter of the dome will be 217 feet with the total dome height at 180 feet (eighteen storys high). The total area the building will take up is 1.44 acres inside a total area of 5 acres.
The centerpiece of the TMT Observatory is to be a Ritchey-Chrétien telescope with a 30-metre (98 ft) diameter primary mirror. This mirror is to be segmented and consist of 492 smaller (1.4 m), individual hexagonal mirrors. The shape of each segment, as well as its position relative to neighboring segments, will be controlled actively.
A 3.6-metre (12 ft) secondary mirror is to produce an unobstructed field-of-view of 20 arcminutes in diameter with a focal ratio of 15. A flat tertiary mirror is to direct the light path to science instruments mounted on large Nasmyth platforms. The telescope is to have an altazimuth mount. This mount will be capable of re-positioning the telescope between any two points of the sky in less than 5 minutes. Once the celestial object is acquired, the telescope will track its motion with a precision of a few milliarcseconds. The moving mass of the telescope, optics, and instruments will be 1430 tonnes. The design of the facility descends from the W. M. Keck Observatory.
Integral to the observatory is a Multi-Conjugate Adaptive Optics (MCAO) system. This MCAO system will measure atmospheric turbulence by observing a combination of natural (real) stars and artificial laser guide stars. Based on these measurements, a pair of deformable mirrors will be adjusted many times per second to correct optical wave-front distortions caused by the intervening turbulence.
This system will produce diffraction-limited images over a 30-arc-second diameter field-of-view, which means that the core of the point spread function will have a size of 0.015 arc-second at a wavelength of 2.2 micrometers, almost ten times better than the Hubble Space Telescope.
Three instruments are planned to be available for scientific observations:
- Wide Field Optical Spectrometer (WFOS) providing near-ultraviolet and optical (0.3–1.0 μm wavelength) imaging and spectroscopy over a more than 40-square arc-minute field-of-view. Using precision cut focal plane masks, WFOS would enable long-slit observations of single objects as well as short-slit observations of hundreds of objects simultaneously. WFOS would use natural (uncorrected) seeing images.
- Infrared Imaging Spectrometer (IRIS) mounted on the observatory MCAO system, capable of diffraction-limited imaging and integral-field spectroscopy at near-infrared wavelengths (0.8–2.5 μm). Principal investigators are James Larkin of UCLA and Anna Moore of Caltech. Project scientist is Shelley Wright of the University of Toronto.
- Infrared Multi-object Spectrometer (IRMS) allowing close to diffraction-limited imaging and slit spectroscopy over a 2 arc-minute diameter field-of-view at near-infrared wavelengths (0.8–2.5 μm).
Additional first-decade capabilities
For planning purposes, TMT has developed concepts for an additional six instruments, which it proposes to be deployed during the first decade of science operations. These plans have been reviewed and updated on a roughly bi-annual basis starting in 2010. In no order of preference, planned additional scientific capabilities include:
- Extremely high contrast (1 part in 108 @ 1.65 μm) exoplanet imaging and spectroscopy at near-infrared wavelengths.
- Diffraction-limited echelle spectroscopy (resolving power ~ 25 000) at near-infrared wavelengths (1.0–2.5 μm).
- Diffraction-limited imaging and echelle spectroscopy (resolving power ~ 50,000) at mid-infrared wavelengths (8–28 μm).
- High precision (~0.01 arcsecond) astrometric imaging and (<<0.001 arcsecond) astrometry at near-infrared wavelengths (1.0–2.5 μm).
- Multiple integral-field unit spectrometers deployable over a 5 arc-minute diameter field-of-view, each with individual adaptive optics correction, at near-infrared wavelengths (1.0–2.5 μm)
Partnerships and funding
The Gordon and Betty Moore Foundation has committed US$200 million for construction. Caltech and the University of California have committed an additional US$50 million each. Japan, which has its own large telescope at Mauna Kea, the 8.3-metre Subaru, is also a partner.
In 2008, the National Astronomical Observatory of Japan (NAOJ) joined TMT as a Collaborating Institution. The following year, the telescope cost was estimated to be $970 million to $1.4 billion. That same year, the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) joined TMT as an Observer.
In 2010, a consortium of Indian Astronomy Research Institutes (IIA, IUCAA and ARIES) joined TMT project as an observer. The observer status is the first step in becoming a full partner in the construction of the TMT and participating in the engineering development and scientific use of the observatory (Subject to approval of funding from Indian Government). Two years later, India and China became partners with representatives on the TMT board. Both countries agreed to share the telescope construction costs, expected to top $1 billion.
The continued financial commitment from the Canadian government had been in doubt due to economic pressures. Nevertheless, on April 6, 2015, Prime Minister Stephan Harper announced that Canada would commit $243.5 million over a period of 10 years. The structure will be built by Dynamic Structures Ltd. in British Columbia, and then shipped to Mauna Kea.
In cooperation with AURA, the TMT project completed a multi-year evaluation of five sites:
- Cerro Armazones, Antofagasta Region, Republic of Chile
- Cerro Tolanchar, Antofagasta Region, Republic of Chile
- Cerro Tolar, Antofagasta Region, Republic of Chile
- Mauna Kea, Hawaii, United States (preferred site)
- San Pedro Mártir, Baja California, Mexico
The TMT Observatory Corporation board of directors narrowed the list to two sites, one in each hemisphere, for further consideration: Cerro Armazones in Chile's Atacama Desert, and Mauna Kea on Hawaii Island. On July 21, 2009 the TMT board announced Mauna Kea as the preferred site. The final TMT site selection decision was based on a combination of scientific, financial, and political criteria. Chile is also where the European Southern Observatory is building the E-ELT. If both next-generation telescopes were in the same hemisphere, there would be many astronomical objects that neither could observe. The telescope was given approval by the state Board of Land and Natural Resources in April 2013. There has been opposition to the building of the telescope, based on potential disruption to the fragile alpine environment of Mauna Kea due to construction, traffic and noise, which is a concern for the habitat of several species, and that Mauna Kea is a sacred site for the Native Hawaiian culture. The Hawaii Board of Land and Natural Resources conditionally approved the Mauna Kea site for the TMT in February 2011. The approval has been challenged; however, the Board officially approved the site following a hearing on February 12, 2013.
The building of the Thirty Meter Telescope on Mauna Kea has sparked protests and demonstrations on the island of Hawaii. Mauna Kea is a sacred mountain to the native Hawaiian people.
On October 7, 2014 the groundbreaking for the TMT was interrupted by demonstrators. In late March 2015, demonstrators halted the construction crews. On April 2, 2015 about 300 protesters gathered on Mauna Kea, some of them trying to block the access road to the summit; 23 arrests were made. Once the access road to the summit was cleared by the police, about 40 to 50 protesters began following the heavily laden and slow-moving construction trucks.
On April 7, 2015 the construction was halted for one week at the request of Hawaii state governor David Ige after the protest on Mauna Kea continued. Project manager Gary Sanders stated that TMT agreed to the one week stop for continued dialogue; Kealoha Pisciotta, president of Mauna Kea Anaina Hou, viewed the development as positive but said opposition to the project would continue. On April 8, 2015, Governor Ige announced that the project was being temporarily postponed until at least April 20, 2015. Construction was set to begin again on June 24, though hundreds of protesters gathered on that day, blocking access to the construction site for the TMT. Some protesters camped on the access road to the site, while others rolled large rocks onto the road. The actions resulted in 11 arrests.
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