The location of the planned Thirty Meter Telescope (TMT) remains in the balance as hearings continue this month in Hawaii over its disputed building permit. But now, at least, astronomers have a backup. The board of the TMT International Observatory announced yesterday that, if Hawaii proves inhospitable, they will build the telescope on the Roque de los Muchachos on La Palma, one of Spain’s Canary Islands off the west coast of Africa.

"The TMT International Observatory Board of Governors has explored a number of alternative sites for TMT. Every site we considered would enable TMT’s core science programs,” board chair Henry Yang, chancellor of the University of California, Santa Barbara, said in a statement. After careful consideration, he said, the board had chosen “Spain as the primary alternative to Hawaii.”

The TMT, which will be one of the world’s largest telescopes when it begins operating next decade, got into hot water because Native Hawaiian activists objected to its siting on Mauna Kea. The mountain is one of the world’s best sites for optical and infrared astronomy but it is considered sacred by many Hawaiians. Activists managed to get the TMT’s building permit overturned by Hawaii’s Supreme Court on a technical issue and hearings are now in progress over the granting of a new permit. Meanwhile, the TMT board had been investigating the suitability of several alternative sites.

At 2400 meters, Roque de los Muchachos is at a much lower altitude than Mauna Kea’s 4050 meters. That will make observing at infrared wavelengths more challenging because infrared is absorbed by moisture in the atmosphere and light will have more atmosphere to travel through to get to a lower observatory. But the site on La Palma has an advantage over the other alternatives: It is already an established observatory, so much of the necessary infrastructure for the TMT is already in place.