The Thirty Meter Telescope, which is intended to be the most advanced optical telescope in the world, is slated to begin construction in the spring of 2018. Astronomers can't wait to use this observatory to comb the universe—it's an international partnership between Canada, the US, Japan, China and India—but the only problem is that, as of right now, no one knows exactly where it's going to be located.
The gargantuan 'scope promises to give humanity unprecedented views of distant galaxies, help characterize alien planets, and to test the fundamental theories of astrophysics. It has faced fierce protests and opposition against its planned location on Mauna Kea in Hawaii, which is a sacred site. The project began in the '90s, but in 2015 the TMT's building permit was revoked. A judge is expected to make a recommendation in the coming months on whether construction should go ahead, but right now, the mega-telescope's fate isn't clear.
Canada has a lot at stake. It's committed some $243.5 million over ten years to the project, and scientists here are anxious to use the instrument to scour the skies. A team of Canadian astronomers has now authored a new report that outlines the costs and benefits of a backup location, should it have to move once and for all, at the Observatorio del Roque de los Muchachos (or ORM) on La Palma in Spain's Canary Islands. Unfortunately for them, it turns out this secondary site is not exactly optimal for a super-advanced giant telescope.
"The main drawbacks of ORM are that it is warm and relatively wet, which makes [mid infrared] observations all but impossible," wrote Michael Balogh, chair of the CASCA/ACURA TMT Advisory Committee (or CATAC) to me in an email.
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The committee was formed in January 2017 and took initiative on investigating a proposed alternative location, once it became clear there would be obstacles to building in Hawaii.
According to their new study, the lower altitude and different climate of the Canary Islands would mean that the TMT's instrumentation design would have to be altered to include more adaptive optics—that is, much more complicated parts of the telescope's mirror, which can morph to account for a more turbulent atmosphere.
"That means it takes longer to achieve the same science compared with [Mauna Kea] or Chile. But for the most part the same science is still achievable," said Balogh.
Last fall, before ORM was chosen, another Canadian group was tasked with giving their recommendation of a potential plan B, and recommended a site in Chile. But when the time came, the TMT International Observatory Board (TIO) chose the Canary Islands site.
One possible reason was to keep the telescope in the Northern Hemisphere. Right now, all of the TMT's possible competitors will be found in Chile. The Giant Magellan Telescope and the European Extremely Large Telescope, currently in similar stages of construction to the TMT, will rival this telescope, and promise to offer excellent views of the southern skies.
"From a global perspective, it makes sense to not put everything in the same hemisphere. There are certainly interesting objects [including the Andromeda Galaxy] observable only in the North," wrote Balogh. "But the stronger argument is synergy with other facilities and surveys that cover the northern sky."
The fall 2016 report found that while operating in La Palma would allow for northern observations, the site could fall short in observing highly prioritized infrared targets—exoplanets.
Balogh could not say exactly what the TIO's motivations were. "We have confidence in our board members and we trust that they cast their vote because it is in the best interest of Canada. There is no frustration at the outcome," he wrote.
The TIO provided a statement from spokesperson Scott Ishikawa. "Canada remains a strong member of our TMT project team and agrees that Mauna Kea in Hawaii is still the preferred site to build the Thirty Meter Telescope. The report recommended building in the Canary Islands only if the Hawaii option does not prove feasible on a timely basis. The goal is to start on-site construction by April 2018."
The disappointment of settling on a scientifically suboptimal site is outweighed by the discoveries that could still be made, wrote Balogh. "As the committee learned more about all the work has been done in the development, we were tremendously impressed and became ever more excited about the project.
"TMT is a truly outstanding, awesome machine. With some very clever design choices, and great instrumentation. It is going to be spectacular, wherever it is sited," wrote Balogh.
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