After 10 years of delay, the controversial Thirty Meter Telescope may finally get built — in Spain

A long-delayed project to build the largest telescope in the Northern Hemisphere atop Mauna Kea in Hawaii has been given new life, as Spain has offered new funding and a new location on the island of La Palma.

The international Thirty Meter Telescope (TMT) was to be built alongside a collection of other astronomical telescopes at an elevation of 4,205 metres atop Mauna Kea on the Big Island of Hawaii. But the mountain is sacred to Hawaiian Indigenous communities, and by trying to push through the project with a disregard to the area’s environmental and cultural importance, construction was stalled before it could begin, and costs have ballooned.

Spain has now made an offer of €400 million ($648 million) to help build the TMT atop Roque de los Muchachos on the island of La Palma, part of the Canary Islands in the Atlantic off the coast of Africa. Already home to more than 20 astronomical telescopes at 2,396 metres, it is not as high as Mauna Kea and the weather isn’t as clear, but it is a good second choice.

However, a Canary Islands environmental group, Ben Magec-Ecologists in Action, have also spoken out against the project’s move to Spain, so it remains to be seen if the TMT organizers have learned from their past mistakes, that it’s cheaper and easier to get everyone on board in the first place.

In the telescope world, size matters. The larger the primary mirror, the more light it can gather, bringing more distant, fainter celestial objects into view. Ever since Galileo pointed his small hand-held telescope at the moon in 1610, instruments have grown larger and larger with solid glass mirrors five metres across. 

For comparison, the largest telescope in Canada, David Dunlap Observatory in Ontario, has a mirror that spans just 1.88 metres.

With the advent of segmented mirrors, using hexagonal pieces that fit together as glass jigsaw puzzles, telescopes have grown to enormous proportions with mirrors as large as a baseball diamond, capable of scanning the sky with 200 times the power of current ground-based telescopes. 

The TMT is one of three of these “megatelescopes” in the works, but the only one in the Northern Hemisphere. The Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT) will both be based in Chile.

Planning for the TMT started more than two decades ago. Several groups and countries came together to fund the project, including Canada, which contributed $243.5 million under the Stephen Harper government in 2015. Since the beginning, Mauna Kea has been considered the best location because of its high elevation above most clouds, and a location in the middle of the Pacific Ocean where the skies are clear most nights of the year.

However, the current observatories on the mountain, which were primarily built from 1967 to 1999, were pushed through without the approval of the Native Hawaiians who consider the mountain sacred. This time, the Indigenous communities were able to take a stand, and have been blocking construction at the site since 2014.

This delay has inflated the cost to $3.9 billion US and put the project in limbo. 

Another blow to the TMT was the recent withdrawal of U.S. support after the current administration made severe cuts to the National Science Foundation in May. Instead, the decision was made to focus efforts on getting the GMT up and running in Chile.

It may seem odd to build giant telescopes on the ground when the James Webb Space Telescope has peered farther into space and farther back in time than any telescope in history. But these new instruments with enormous mirrors six times bigger than Webb should be able to match or exceed its performance. 

The other advantage of ground-based telescopes is that they can be serviced regularly, extending their lifetimes to many decades, and new instruments can be added as technology evolves. Webb is completely out of reach on the other side of the moon and expected to last perhaps another decade, depending on when its fuel runs out.