If you are going to spend more than a billion dollars building one of the world's biggest telescopes, you'll want to put it in a place with the best possible view of the stars. But in the case of the Thirty Meter Telescope (TMT), an instrument that promises unprecedented images of everything from the most distant galaxies to nearby exoplanets, builders may have to settle for second best.
Next week, the fierce legal and cultural battle that has engulfed efforts to build the TMT on Mauna Kea, a 4207-meter-high peak in Hawaii, will reignite as state officials open a pivotal hearing on whether to allow construction. The peak is rated as the best observing site in the Northern Hemisphere, but for Native Hawaiians it is sacred land, and many residents oppose the project. "The risk [to the project] is by no means small," says project manager Gary Sanders of the TMT International Observatory in Pasadena, California, and "the cost of delay is significant." So the project is also hedging its bets by considering alternative sites.
The TMT is one of three giant telescopes expected to dominate ground-based optical astronomy beginning in the next decade. The European Extremely Large Telescope (with a 39-meter mirror) and the Giant Magellan Telescope (24.5 meters) are already under construction, both in Chile. The TMT was also supposed to be underway by now, having won a construction permit from Hawaiian officials in 2011 after a long approval process. But the project ground to a halt after Native Hawaiian protesters disrupted a 2014 groundbreaking ceremony and later blocked workers from reaching the site. Then in December 2015, native activists won a ruling from Hawaii's supreme court that invalidated the TMT's building permit because of procedural violations. The court ordered the state's Board of Land and Natural Resources to reopen hearings designed to give the public a voice in the decision.
The sky's the limit
|Mauna Kea, Hawaii||4050|
|San Pedro Mártir, Mexico||2830|
|Roque de los Muchachos, Spain||2400|
|Antofagasta region, Chile||2300–4500|
The new hearings begin on Hawaii's Big Island on 18 October and will last into late November. Sanders says the TMT's application is essentially unchanged. Witnesses have already supplied written statements, and more than a dozen parties, mostly opposing the project, will have a chance to ask questions. In the end, "it seems likely we'll get the permit," says astronomer Robert Kirshner, head of science programs at the Gordon and Betty Moore Foundation in Palo Alto, California, which has so far ploughed $180 million into the TMT. But any decision, which is unlikely before the end of the year, will probably end up again in Hawaii's supreme court.
Even if the TMT ultimately gets a go-ahead, supporters worry that continuing opposition may make it difficult to build, staff, and operate the telescope. Protests on the mountain have become heated at times, according to press reports, and there have been arrests. "We can't take risks with people's safety," Sanders says.
If Hawaii proves inhospitable, the TMT will try to relocate. Since this past February, experts have been reviewing alternative sites, including several that were studied when the TMT began serious planning in the mid-2000s. Cerro Armazones, a peak in northern Chile, was a favorite for the TMT, but it is now ruled out because Europe's giant scope is taking up residence. Other sites nearby are in contention. But moving the TMT to Chile would put all three giant telescopes in the Southern Hemisphere, where they would be unable to see much of the northern sky.
Potential Northern Hemisphere sites include San Pedro Mártir in Baja California in Mexico and Roque de los Muchachos on La Palma, a Spanish island off the Atlantic coast of Morocco. "Our friends in La Palma are pushing hard" to get the TMT, says Matt Mountain, president of the Association of Universities for Research in Astronomy in Washington, D.C. But neither alternative matches the seeing conditions on Mauna Kea, and they would bring extra cost and complication. The project has already ruled out sites in the Himalayas, put forward by India and China—both TMT partners along with the United States, Japan, and Canada—because they are too far from ports and have short construction seasons.
The TMT governors are expected to choose their top alternative site later this month. Regardless of what happens in Hawaii, the governors have vowed to start construction—on Mauna Kea or elsewhere—no later than April 2018.
Previous coverage of the Thirty Meter Telescope: