One year out from the time Thirty Meter Telescope officials are insisting that construction must begin, the TMT International Observatory board is making the case for why a mountain in the Canary Islands will be an “excellent” alternative site for the $1.4 billion next-generation telescope.

What’s more, lawmakers in Spain, which controls the Canary Islands, have embraced the project, according to news reports, and managers at the Observatorio del Roque de los Muchachos on La Palma island are indicating they are willing to expand the observatory’s boundaries and infrastructure in case the telescope lands on their mountain.

TMT officials presented the case for the alternative site in the March newsletter of the National Optical Astronomy Observatory, a TMT associate member, and in documents recently posted on the TMT.org website.

In the newsletter, TMT officials said Mauna Kea remains their top choice for the telescope, and they are committed to the legal process now playing out in Hawaii.

However, they reiterated that the board has a “firm goal” of starting construction in April 2018, and, to make that possible, “reasonably assured access” to a site is required by fall of this year.

This is necessary, they said, to allow for submitting budget proposals to the financial authorities of the various project partners, including science institutions in Canada, Japan, China and India, plus the California Institute of Technology and the University of California.

“To start construction by April 2018 will require some appropriate lead time,” TMT spokesman Scott Ishikawa said Monday. “This is why TMT is pursuing an alternative site — to ensure a location will be available on the planned start date.”

However, an April start date in Hawaii remains quite uncertain at this point.

The project is still tied up in the contested case hearing do-over required by the Hawaii Supreme Court following the state’s error in the permitting process. While the testimony phase of the hearing is over, the parties are still working to finalize the record before the hearing officer makes a final recommendation to the state Board of Land and Natural Resources.

After that, an appeal to the state’s highest court is highly likely.

On top of that, another contested case hearing has been ordered by a circuit judge to address a due-process issue in regard to the TMT’s sublease with the University of Hawaii. The state is appealing the ruling.

In the meantime, TMT has its backup site: Observatorio del Roque de los Muchachos, home to 12 telescopes, including the 10.2-meter Gran Telescopio de Canarias, and recently selected site of the Cherenkov Telescope Array, which is set to become the largest ground-based gamma-ray detection observatory in the world.

In the NOAO newsletter, TMT-affiliated scientists Michael Bolte, Christophe Dumas and Mark Dickinson wrote that the Canary Islands site is the best place to accomplish a quick start in the event Hawaii doesn’t work out.

It also has the shortest projected construction schedule, they said, in part because of how accessible the site is and because of the existing infrastructure in Tenerife, the most populous island in the Canary Islands, and Santa Cruz de la Palma, the principal city of La Palma.

A TMT report puts a 2027 target date on development in La Palma, compared with the 2024 date set for Hawaii before construction was blocked.

The astronomers said TMT’s study of the La Palma site indicates it will indeed support TMT’s core science programs, offering excellent astronomical observing conditions, particularly in regard to “adaptive optics” that reduce atmospheric disturbance.

The study also shows that atmospheric turbulence compares to Mauna Kea and that other key characteristics are nearly as good. In addition, the fraction of usable nights is the same for both sites: 72 percent.

There’s a perception that dust from the Sahara Desert can significantly affect observations in the Canary Islands, they said, but a study found that dust on the mountain is comparable to Mauna Kea.

At 7,874 feet, La Palma’s elevation is substantially lower than Mauna Kea’s 13,796 feet. That’s not ideal, they conceded, because warmer temperatures increase the “thermal background” that affects observations at certain wavelengths.

There’s also more moisture in the air at the lower altitude, which can result in higher atmospheric pressure that can compromise performance at mid-infrared wavelengths.

Still, some of the site’s flaws can be compensated for by operating on a flexible schedule to take advantage of the best conditions, according to the scientists.

Serious site concerns

One of the primary reasons TMT officials chose the Canary Islands, they said, is because it was important to remain in the Northern Hemisphere to balance the fact that the two other next-generation Extremely Large Telescope projects, the European-Extremely Large Telescope and the Giant Magellan Telescope, are being built in Chile in the Southern Hemisphere. By remaining in the north, the TMT will be able to scan a part of the sky that the other big telescopes won’t be able to see.

But Thayne Currie, a Mauna Kea astronomer who also belongs to a group called Yes2TMT, said he has serious concerns about TMT’s scientific capability were it to be placed on La Palma.

“I’ve seen multiple sources of site data for La Palma,” Currie said. “La Palma is nowhere near as good as the TMT site on Mauna Kea. Mauna Kea is vastly superior at thermal infrared wavelengths where we have learned a lot about the chemistry of planets and brown dwarfs. Mauna Kea is superior in the near-infrared, which probe biomarkers for Earth-like planets we want to image with TMT.”

Meanwhile, Spain’s Senate earlier this month unanimously approved a motion urging the government to carry out all efforts necessary to make the Canary Islands the new home of the TMT. The Spanish Congress of Deputies offered its formal support in November.

According to news reports in the Canary Islands, local officials are willing to expand the limits of the mountaintop astronomy zone, build a new road and triple the power source to accommodate the TMT.

TMT officials are now working to complete a hosting agreement and to carry out the permitting process for that site, the scientists said, adding that detailed planning for construction at La Palma is also underway.