In what seems akin to winning the lottery, astronomers are moving ahead with not one, but three gigantic optical-IR telescopes, each with a price tag upwards of a billion dollars. The European Extremely Large Telescope (E-ELT) and the Giant Magellan Telescope (GMT) are both sited in Chile, and the Thirty Meter Telescope (TMT) is to be built on Mauna Kea in Hawaii.
For a given wavelength, the diffraction limit, which sets a telescope’s maximum possible resolution, shrinks as the primary mirror grows. “We will be able to take exquisitely sensitive images back to the beginning of the observable universe,” says TMT board member Michael Bolte of the University of California, Santa Cruz. With adaptive optics, the ground-based telescopes will have spatial resolution exceeding that of the Hubble Space Telescope by at least a factor of 10 and topping that of the 6.5-m James Webb Space Telescope (JWST), scheduled to launch in 2018.
The billion-dollar scale raises questions, says Matt Mountain, president of the Association of Universities for Research in Astronomy. “What are the appropriate funding models? It’s fair to ask if we have enough resources globally to build, operate, and adequately instrument three of these as completely independent entities.”
The science goals are similar for the three telescopes: They will be used to search for biomarkers in the atmospheres of extrasolar planets and to study black holes, dark matter, dark energy, star and galaxy formation, the era of re-ionization, and more. But the telescopes differ in design, instrumentation, approaches to adaptive optics, and funding and organizational structures.
Each project faces its own technical, financial, and social hurdles; in particular, the GMT still has half a billion dollars to raise, and some native Hawaiians strongly oppose the building of the TMT on a mountain they hold sacred. But to first order, says Jochen Liske, acting program scientist for the E-ELT, “The challenge for all three projects is getting things right and producing a telescope that works.” They all aim to have first light in the early to mid 2020s.
Will US government buy in?
So far the US government is not a partner in any of the projects, although both the TMT and GMT began in the US. A National Academy of Sciences committee, in its April report Optimizing the U.S. Ground-Based Optical and Infrared Astronomy System, recommends that NSF plan for an investment in one or both telescopes to “capitalize on these observatories’ exceptional scientific capabilities for the broader astronomical community … for example, through shared operations costs, instrument development, or limited term partnerships in telescope or data access or science projects.”
In 2013 NSF awarded $1.25 million over five years to the TMT to explore ways the agency might participate in the project at the $100 million level. But it’s not going to happen, says Vernon Pankonin, a senior adviser in NSF’s division of astronomical science. “NSF does not have money to participate in a meaningful way.”
Biggest and best funded
At 39 m across, the E-ELT will be the largest of the telescopes (see figure below). It is being built on Cerro Armazones in northern Chile by the European Southern Observatory (ESO) for astronomers in the organization’s 16 member countries and Chile.
The European Extremely Large Telescope is under construction on Cerro Armazones, Chile. (Artist’s conception courtesy of ESO/L. Calçada.)
The European Extremely Large Telescope is under construction on Cerro Armazones, Chile. (Artist’s conception courtesy of ESO/L. Calçada.)
Because it’s not currently technically possible to make a 30-m monolithic mirror, all the extremely large telescopes use segments. The E-ELT’s primary mirror will consist of 798 hexagonal tiles, each 1.42 m diagonally across.
Early on, ESO envisioned a larger telescope—first a diameter of 100 m and then 42 m. It was trimmed to 39 m to reduce both cost and technical risk. “The size of the telescope did not come out of thin air,” Liske says. “It is based on the extrasolar planet science case. At 39 m, we think we can resolve a two-Earth-mass planet in the habitable zone from its parent star at a distance of 25 light-years from Earth.” That’s “our front yard,” he adds. “The Milky Way is 100 000 light-years across. Studying extrasolar planets in our immediate vicinity is the best we can do with the available resources.”
Like the other two extremely large telescopes, the E-ELT will use a mix of adaptive optics techniques to correct for atmospheric distortions. Both bright natural stars and artificial laser guide stars will be used to measure distortions. The artificial stars are created using 20-W lasers to excite sodium atoms in a layer of meteoric dust at altitudes of 90 km. The method opens up most of the sky to turbulence correction rather than limiting astronomers to looking near natural bright stars. TMT team member Andrea Ghez, an astronomer at the University of California, Los Angeles, says laser guide stars took adaptive optics “from a cute trick that affected a small fraction of astronomers to an everyday technique.” Using multiple lasers, as all three of the extremely large telescopes will, “is the next fertile step,” she says. “You can improve contrast to see faint objects next to bright ones and it makes you more sensitive to atmospheric blurring at shorter wavelengths.”
A telescope’s adaptive optics design depends on the science, explains Liske. “Do you want to have a super-well-resolved image in only one direction? Or do you want a good but perhaps not perfect image over a wider field of view?” The E-ELT design opted for a built-in 2.4-m deformable mirror that allows for wide-field correction. The telescope will also have corrective optics modules tailored to its measuring instruments. Two instruments are planned for first light in 2024: a diffraction-limited camera and an intermediate-resolution spectrograph that obtains a spectrum from each object in its field of view.
The ESO council approved the E-ELT design in 2012, but the team was left chomping at the bit. The holdup was money: To start construction, the project had to have 90% of the €1.1 billion ($1.2 billion) total cost in hand. In December 2014 the council gave its blessing to a two-step scheme, which defers 10% of the telescope components if necessary. For example, says E-ELT program manager Roberto Tamai, an adaptive optics module, spare segments for the primary mirror, and a power conditioning system could be postponed. Deferring those items would not affect achievement of first light, he says, and the two-phase process allows the start of construction. After the council gave the nod, he notes, the process of Brazil’s joining ESO, which had been stalled, has sped up. “Once Brazil joins—or some other country accedes to ESO,” Tamai says, “we will have the money to complete the program.”
Earlier this year, some 18 m was shaved off the mountaintop to create a platform in preparation for the telescope. “We are in the final steps of building a road, about to sign agreements for the first three instruments, and near the end of procurement for the main structure and dome,” says Liske. He notes the urgency of completing the extremely large telescopes in time for them to overlap and work together with the JWST.
Fundraising is top priority
In November the GMT team will hold a groundbreaking ceremony at Las Campanas, Chile, a few hundred kilometers south of the E-ELT site. “Something that is really important to our strategy is having a significant leap in light gathering and resolution sooner rather than later,” says Taft Armandroff, director of the University of Texas (UT) McDonald Observatory and a member of the GMT board. “We are committed to working fast and being first—even if it’s not full size, even without adaptive optics, and with only two instruments.”
The GMT design consists of seven 8.4-m mirrors—a central mirror surrounded by the other six—that together form a primary mirror with an effective diameter of 24.5 m. The six outer mirrors are off-axis, each oriented differently. The plan is for the GMT to start collecting data with four mirrors—and an effective diameter of 16 m—in 2021, with the telescope to be completed by 2024.
“We have been making remarkable progress,” says the University of Chicago’s Wendy Freedman, who until recently was chair of the GMT board. “No one has ever done off-axis mirrors of this size. In the end they operate as one piece of glass.” So far, three mirrors have been cast (see photo on page 2). The initial instruments planned for the GMT are a high-resolution spectrograph and a wide-field multiobject spectrograph.
Inspectors check out the back of one of seven 8.4-m mirrors that will make up the primary mirror of the Giant Magellan Telescope.
Inspectors check out the back of one of seven 8.4-m mirrors that will make up the primary mirror of the Giant Magellan Telescope.
Like the other extremely large telescopes, the GMT will incorporate and scale up mainly proven technologies. For example, says Armandroff, “we are hoping to use more sophisticated mirror coatings than aluminum.” A high-tech multilayer silver coating would, he says, provide better reflection in the IR without tarnishing. And one GMT instrument will use silicon gratings because they allow more flexibility in groove spacing than glass. That flexibility, he says, “will be helpful for IR observations.”
The GMT currently has 11 institutional partners in four countries. The US partners are the Carnegie Institution of Washington, Harvard University, the Smithsonian Institution, the University of Arizona, the University of Chicago, Texas A&M University, and UT Austin. In addition, Australian National University, the nonprofit Astronomy Australia Limited, the Korea Astronomy and Space Science Institute, South Korea’s national research institute, and the São Paulo Research Foundation in Brazil are members. The partners’ pledges range from $40 million to $80 million. The GMT is run centrally, with a cash in, contracts out approach.
“When São Paulo joined the GMT [in July 2014], it was kind of dramatic for us,” says Robert Kirshner, a former GMT board member who is now chief program officer for science at the Gordon and Betty Moore Foundation. “It cleared the way for UT to come through with $50 million, and that put us over the goal for starting construction.” So far, the project has pledges of $500 million, or about half the total estimated cost of $1.05 billion. “Our number one priority is fundraising,” Armandroff says.
Northern Hemisphere
The TMT grew out of the Keck telescopes in its design, collaboration, and funding sources. The University of California and Caltech were the original partners, each with a 12.5% share, and the Moore Foundation was a big donor. The primary mirror design is similar to that of the E-ELT but smaller, with 492 tiles and an overall diameter of 30 m (see photo above). The TMT is the only one of the extremely large telescopes that will have full access to the Northern Hemisphere skies.
Some 492 glass segments, each 1.42 m in diameter, will make up the primary mirror of the Thirty Meter Telescope. These circular blanks will be cut to form hexagonal tiles. They were made in Japan, which is contributing a quarter of the cost to build the TMT; among Japan’s other contributions is the main structure for the telescope.
Some 492 glass segments, each 1.42 m in diameter, will make up the primary mirror of the Thirty Meter Telescope. These circular blanks will be cut to form hexagonal tiles. They were made in Japan, which is contributing a quarter of the cost to build the TMT; among Japan’s other contributions is the main structure for the telescope.
Partnering with the California universities on the TMT are Canada, China, India, and Japan. So far, the collaboration has 80% of the estimated $1.4 billion it needs.
In the TMT model, 25–30% of each partner’s contributions are in cash, with the rest in kind. For example, Canada’s contributions include a near-field IR adaptive optics system, the telescope’s enclosure, and parts of one of three first-light instruments. China’s include the tertiary mirror system, adaptive optics lasers, and a cooling system for the telescope electronics.
China joined the TMT rather than the GMT largely because of the in-kind contributions. “One crucial goal is to improve our capabilities in technology, science, and management,” says board member Shude Mao of Tsingua University and the National Astronomical Observatory of China. “We don’t want to send only cash. We want to build up our industry and know-how.”
Opposition mounts
Protests have stalled the TMT. Opposition to telescopes on Mauna Kea and other mountains is not new (see Physics Today, December 2003, page 35). “We realized we had to do something differently if we would ever hope to get through the regulatory process,” says Bolte. “We worked with people in the community.”
The TMT organization consulted cultural practitioners and studies of plants and animals in the summit area to choose a site that was “environmentally and culturally less sensitive,” he says. The organization also created a fund of $1 million a year to encourage K–12 children to pursue science, technology, engineering, and mathematics and a separate fund to train local students for technical jobs. The TMT pays an annual leasing fee of $1 million, of which 80% goes for stewardship of the mountain. That includes, for example, money for rangers and a station to clean off vehicles in an effort to curb the spread of invasive species on the mountain.
Construction was put on hold after demonstrators blocked the site in April. On 26 May Hawaii governor David Ige gave his nod to the project. At the same time, he asked the University of Hawaii, which holds the master lease for the science reserve on Mauna Kea, to take 10 steps to improve its stewardship of the mountain.
When the TMT attempted to restart construction on 24 June, though, protestors were waiting; 11 were arrested. One protestor, Shelley Muneoka, told the Canadian radio program As It Happens that the goal of the protests is to “stop the construction of the Thirty Meter Telescope … primarily for religious and environmental reasons.”
On that day, TMT international observatory board chair Henry Yang issued a statement saying that the construction crew was brought down from the mountain for their safety and that “we are planning to resume when the issue is resolved…. We respect their [the protestors’] views and, looking toward the future, we hope we can work together to find common ground.”
“There is a tremendous sense of frustration,” says Caltech astronomer Judith Cohen. “We felt that after 10 years of running around making deals and accommodating, we had nailed things down.” Still, says Bolte, “there is no value in rushing. This process has to play out and get sufficient buy-in so it’s a durable solution.”
The non-US partners in the project are keeping their cool. “We understand construction will have twists and turns,” says Mao. “Personally, I am not too alarmed.”
The site delays are not yet a problem for the overall timing of the project, says Bolte, noting that construction will take about eight years once it begins.
