Protests and legal battles have halted construction of the Thirty Meter Telescope in Hawaii. Credit: Holly Johnson/AP/PA Images

Hawaii's supreme court has ruled that the construction permit for the Thirty Meter Telescope (TMT) on top of the mountain Mauna Kea is invalid. The 2 December decision is a major blow to the international consortium backing the US$1.5-billion telescope, and a win for the Native Hawaiians who have protested against its construction on what they regard as a sacred summit.

The mountain-top battle over the Thirty Meter Telescope

Hawaii's Board of Land and Natural Resources should not have approved the permit in 2011, the court said, because it did so before protestors could air their side in a contested case hearing.Quite simply, the Board put the cart before the horse when it issued the permit,” the court decision reads. “Accordingly, the permit cannot stand.”

"TMT will follow the process set forth by the state, as we always have," TMT board chair Henry Yang said in a statement. "We are assessing our next steps on the way forward."

Construction blocked

It is unclear whether and how the TMT will move forward given the new ruling. Work on the telescope's components has continued at sites outside Hawaii, but the court's decision to block the construction permit is a significant setback. To proceed, the project would have to acquire another permit from the board.

An artist's rendering of the yet-unbuilt Thirty Meter Telescope on Mauna Kea in Hawaii. Credit: TMT International Observatory

Part of the planned TMT site, just below Mauna Kea's 4,200-metre summit, has been cleared, and construction was to have begun last April. But those plans are on hold as protestors have blocked the roads to the site and pursued legal avenues to halt the project.

The TMT would be the Northern Hemisphere counterpart to two other next-generation telescopes, the European Extremely Large Telescope and the Giant Magellan Telescope, now under construction in Chile.

Culture clash

But the TMT faces unique battles at Mauna Kea, which many Native Hawaiians have long argued should not be desecrated by astronomical observatories. Thirteen observatories — one with multiple telescopes — currently sit on the mountain in a science reserve operated by the University of Hawaii. One existing telescope is being dismantled and two others are slated for decommissioning, after the fight over the TMT accelerated plans to limit development on the mountain top.

Hawaiian telescope fight prompts new rules for Mauna Kea

Because the mountain pokes out from the middle of the Pacific Ocean, the skies above Mauna Kea are among the clearest in the world. Some Native Hawaiians say that the benefits to astronomy do not outweigh the need to respect and protect the natural and cultural environment. Many took to social media to praise the court's decision.

TMT's partners are the University of California and the California Institute of Technology, along with research entities from the governments of Canada, China, India and Japan.