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GMT illustration
The Giant Magellan Telescope will feature seven mirrors, each more tha eight meters in diameter. (credit: GMT Organization)

A helping hand for giant telescopes


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The decadal review for astrophysics, widely known as “Astro2020,” is ramping up after a bit of a delay because of the recent government shutdown (a deadline for white papers on various science topics to be considered by the survey was recently extended to March 11.) Much of the attention on Astro2020 will be devoted to deliberations on which large-scale strategic, or flagship, mission it will recommend for development later in the 2020s and into the 2030s, with four concepts currently under study (see “Selecting the next great space observatory”, The Space Review, January 21, 2019.)

There is, though, much more to the decadal than that. The astrophysics decadal, to a degree not matched by other such studies in the space sciences, also focuses on prioritizing development of ground-based telescopes for astronomical research, guiding future investments in them by primarily the National Science Foundation (NSF).

“This is our only chance to be involved in these big telescopes for the US as a whole,” said Elmegreen.

At last month’s meeting of the American Astronomical Society (AAS) in Seattle, there was a major push to win support for two observatories already in development: the Giant Magellan Telescope (GMT) under construction in Chile and the Thirty Meter Telescope (TMT) planned for Hawaii. Both observatories, dubbed extremely large telescopes or ELTs because of the sizes of their primary mirrors, are well into development and would seem likely to continue regardless of what Astro2020 has to say about them.

That’s in large part because both observatories are private ventures. GMT is run by a consortium of universities and organizations in the United States, Australia, Brazil, and South Korea. TMT’s consortium includes universities and organizations in the US, Canada, China, India, and Japan. Those groups are responsible for raising the funding needed to build and operate those facilities.

While those consortia include a number of major American universities (such as the Universities of Arizona and Chicago and Harvard University for GMT, and Caltech and the University of California for TMT) neither includes the NSF nor other US government agencies. That means, for American astronomers, they won’t have access to either the GMT or TMT unless they’re affiliated with one of those universities or have a collaborator who is.

That’s led to an initiative to provide some degree of “open access” for American astronomers to those observatories. “What are our choices for the 2020s and 2030s?” asked David Silva, director of the National Optical Astronomy Observatory (NOAO), which operates several existing open access observatories, during a session of the AAS meeting.

One option, he said, was for the NSF to stay on the sidelines and not support either GMT or TMT. “What that essentially means for the open access community—many of you sitting in the room—is that we will cede ELT science to the Europeans and to other GMT and TMT partners,” he said. The reference to Europe was to the European Extremely Large Telescope (E-ELT) under construction in Chile by the European Southern Observatory.

“The other choice, roughly speaking, is an NSF partnership with GMT and TMT,” he said. Under that concept, known as the US Extremely Large Telescope Program, NSF would provide funding to GMT and TMT in exchange for a share of observing time on them that would be available to American astronomers regardless of whether their institution is a partner in either telescope.

The concept, as currently envisioned, would invest a total of $1 billion of NSF funding into the two telescopes, in exchange for a 25 percent share of time on each. “This sounds like a big number,” Silva acknowledged, “but this is consistent with investments that the NSF has made in last decade, last 15 years, to achieve major scientific facilities.” Among the examples he cited was the Laser Interferometer Gravitational-Wave Observatory (LIGO), whose discoveries of gravitational waves netted a Nobel Prize in physics, and the Large Synoptic Survey Telescope under construction in Chile.

Silva said that while astronomers should advocate for the US ELT Program for Astro2020, they would also need to advocate for an increase in NSF’s budget to implement any recommendation for it that might emerge from the decadal. “The pie has to increase,” he said of the NSF budget. “Right now, it really doesn’t have a robust enough budget to actually multi-billion-dollar facilities without putting unacceptable pressure on grants, for example.”

“There’s real advantages to knowing that the entire US community is behind us and will help us set appropriate priorities,” said GMT’s McCarthy.

Later in that AAS session, astronomers discussed the science that GMT and TMT could perform, from studies of potentially habitable exoplanets to seeking the first stars in the universe. Much of that research, they noted, simply couldn’t be done with smaller telescopes, or would require so much observing time on them to be impractical. “You cannot do the proposed science here with smaller telescopes. It’s not actually possible,” said Quinn Konopacky, an astronomer at the University of California San Diego who studies exoplanets.

TMT illustration
Construction of the TMT atop Mauna Kea is set to resume as soon as this spring after the project cleared legal challenges. (credit: TMT)

A town hall meeting later the same day at the meeting also discussed the benefits of the US ELT Program to a standing-room-only audience (the free food and drink no doubt aided attendance.) “It quickly became obvious that the extremely large telescopes would be driving ground-based astronomy in the immediate future, and now is the time to get involved,” said Debra Elmegreen, chair of the board of Association of Universities for Research in Astronomy (AURA), on the planning that led to the US ELT Program proposal.

Supporting both GMT and TMT, rather than just one of them, offers various advantages, she said. That includes coverage of the full sky—GMT is in the southern hemisphere and TMT is in the northern—as well as coordinating on instrument design. The two telescopes could also do “time domain” astrophysics, given the difference in longitude between the two.

“This is an opportunity—a very rare opportunity—to significantly broaden the US public access in the next generation of US ground-based optical/infrared telescopes,” she argued. “This is our only chance to be involved in these big telescopes for the US as a whole.”

So what’s in it for GMT and TMT, if they’re already working on their telescopes? One advantage is that coordination Elmegreen referred to, allowing the two observatories to work together to optimize their instrument suites and avoid unnecessary duplication. “There’s real advantages to knowing that the entire US community is behind us and will help us set appropriate priorities,” said Pat McCarthy, vice president of the GMT, in an interview during the AAS meeting. “We can work together more effectively on common technical problems.”

There’s also another practical advantage to the US ELT Program: money. Both GMT and TMT are working to raise money for their observatories, each expected to cost more than $1 billion, and neither is fully funded yet.

“There’s a lot more fundraising to do and there’s a lot of effort involved,” Elmegreen said. “But they’re well on their way, and the NSF can put them over the top to make this all a reality.”

“It takes a long time to either bring on new university partners to build relationships with philanthropists. These are the kinds of things that don’t happen overnight,” McCarthy said. “These things do take time.”

He said that the US ELT Program could provide GMT with long-term stability. “It’s an organization that you can count on being there for the long term, to be a steady, stable partner,” he said of the NSF. “That’s very important for any large project like this.”

An additional complicating factor for the TMT, besides the need to raise money, are political and culture issues. An initial effort in 2015 to start construction of the observatory atop Hawaii’s Mauna Kea was blocked by protestors from native Hawaiian groups, who consider the mountaintop sacred. Hawaii’s Supreme Court later revoked a building permit for TMT because of procedural issues by the state government.

TMT went back and, through the state’s Board of Land and Natural Resources, received another permit to build the observatory. The state Supreme Court validated that decision in October 2018, clearing the way for construction of the telescope to start again.

“Nothing that is being planned for space will be able to touch this science until probably the 2040s,” Konopacky said.

TMT officials, speaking on background at the AAS meeting, said they’re working now to finalize the last permits needed from state and local officials before starting construction. That construction could begin as soon as the spring, they said, although they don’t know what sort of protests that new attempt might generate. They cited a poll last year, though, that found that a large majority of Hawaiians, including native Hawaiians, supported construction of the TMT.

TMT does have the option of switching to a backup site on La Palma in the Canary Islands, and has been working to get permits in place there. Hawaii, though, remains the preferred site.

Astronomers who are not involved in the GMT and TMT consortia are anxious to win NSF funding for open access to them because they promise to be the most powerful telescopes they will have access to for decades, including NASA facilities in space. While both GMT and TMT will enter service around the mid-2020s, the flagship mission selected in Astro2020 won’t fly before the mid-2030s—and perhaps much later, given the delays experienced by missions like the James Webb Space Telescope.

“Nothing that is being planned for space will be able to touch this science until probably the 2040s,” Konopacky said. “So if you want leadership in exoplanet science for the next two decades, you’re going to need the TMT and the GMT.”


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