For more than a quarter-century, workers have been toiling atop a mountaintop in Chile in a quest to help researchers explore the universe in the search for the origins of life.

They have finally completed the University of Tokyo’s Atacama Observatory, waiting only for an infrared telescope employing a mirror more than 6 meters in diameter to be installed.

The observatory, known as the TAO, is located on the summit of the 5,640-meter high Mount Chajnantor in the barren Atacama Desert, the driest region on Earth.

About 200 officials from the university, Japan’s education ministry and the Chilean government attended a ceremony to mark the completion of the facility in Santiago in late April.

Julio Bravo Yubini, a senior official with the Chilean foreign ministry, said in his address that he hopes that the TAO telescope, one of the world’s finest infrared instruments, will achieve breakthroughs in the exploration of the universe.

The project began in 1998 with construction of a temporary road to transport building materials to the summit. At those rarefied heights, there is only about half as much oxygen as at ground level, making construction work exceedingly laborious.

About 350 workers, including 120 Japanese, were involved.

“All the workers carried oxygen tanks on their backs to ward off altitude sickness,” recalled Takashi Miyata, director of the TAO, who specializes in infrared astronomy.

In the winter, the temperatures drop and the snow does not readily melt as at lower elevations.

Despite the inhospitable environment, the project progressed and workers installed a 1-meter diameter telescope in 2009, winning Guinness World Records recognition as the Highest Astronomical Observatory in the world.

Still, the TAO project had to overcome more stumbling blocks.

“We had to struggle through social unrest in Chile and the coronavirus pandemic,” Miyata said.

Now, the observation and operation building has been completed alongside a facility that will house a telescope with a primary mirror measuring 6.5 meters across. The instrument is scheduled to be installed this fall at the earliest.

The University of Tokyo selected Chile, a nation in the Southern Hemisphere, as the site of its outpost.

Japan’s National Astronomical Observatory operates the Subaru 8.2-meter optical-infrared telescope in Hawaii. It will become possible for Japanese scientists to cover the universe with the telescopes located in the opposite hemispheres.

Scientists at the university preferred Mount Chajnantor to other candidate sites in the Southern Hemisphere because the atmosphere around the mountaintop is thin and the mountain's location in the arid conditions. 

Only a small portion of infrared radiation from the universe reaches the Earth’s surface after a large percentage of it is absorbed by water vapor in the atmosphere.

According to the University of Tokyo, the Subaru telescope, situated at an altitude of 4,200 meters, collects only 5 percent of the mid-infrared with a wavelength of 31.5 micrometers.

The figure is down to almost zero for the European Southern Observatory’s Very Large Telescope, or the VLT, located at an altitude of 2,600 meters on Cerro Paranal in the Atacama Desert.

But the TAO can detect 40 percent of the mid-infrared light in that range.

As for near-infrared light, whose wavelength is shorter than mid-infrared, the TAO telescope can observe the spectral region seamlessly and with high sensitivity.

Covering a larger field of view, the telescope is expected to perform admirably when it comprehensively monitors a region of the sky.

“We chose a dry region with lesser water vapor, based on data gathered by weather satellites and other sources,” said Yuzuru Yoshii, professor emeritus of cosmic physics at the University of Tokyo, who led the TAO project over the past 26 years.

“The telescope will be installed at an altitude higher than any other observatory in the world, the best possible setting that will enable the infrared telescope to demonstrate its maximum capabilities.”

EXPANDING KNOWLEDGE OF UNIVERSE

On the Atacama Desert plateau, the Atacama Large Millimeter/Submillimeter Array, known as ALMA, is situated, the work of an international consortium of research institutions, including those in Japan, the United States and EU countries.

The ALMA transformative radio telescope can study cosmic light on the boundary between radio waves and infrared light.

Scientists at the University of Tokyo hope that combining observations of the same region of space by the ALMA and TAO will deepen their understanding of the universe.

The TAO will be fully operational in 2025.

The TAO telescope is not among the world’s top 10 infrared telescopes in terms of the primary mirror's diameter. 

But it is unrivaled in its infrared capabilities, matching that of space-borne telescopes.

It also has an edge over space-based instruments in that a ground-based telescope can remain operational for decades through upgrades. 

NASA’s space-borne James Webb Space Telescope has a life span of 10 years or so in orbit. 

The main purpose of the TAO project is to uncover two lingering mysteries: the origins of the universe and galaxies as well as the origins of planets.

By capturing the object in mid-infrared, scientists can observe low-temperature celestial bodies and substances. They will work to unravel the process of how planets were born through the investigation of dust around the stars.

Scientists may possibly gain clues about how galaxies were formed by conducting survey observations in the near-infrared with high sensitivity and a larger field of view.

The observatory operated by the University of Tokyo offers opportunities to its own researchers, allowing them to collect data on specific astronomic objects for a prolonged period.

They can explore how the universe evolved with the precise observation of supermassive black holes countless light-years away and the nature of mystery-shrouded dark energy.

“We believe that if we measure the accurate distances between astronomical objects, that will lead us to have a more complete picture of the structure and expansion of the universe,” Miyata said.

Scientists with the TAO project will be granted 42 to 47 percent of the telescope’s observing time.

Researchers in Japan will be allotted 33 to 38 percent of the remaining telescope time. 

Young researchers, including graduate students, will have access to a certain percentage of this time, an initiative aimed to develop a new generation of astronomers.

Chilean scientists will be granted 10 percent of the observing time, while astronomers in Japan and outside of Japan can have access to the telescope during 5 to 15 percent of the observing time for a fee.

With the project largely completed, Yoshii said he feels rewarded for persevering despite numerous challenges he and his colleagues had to overcome.

“Some criticized the project as reckless, while others questioned its necessity,” he said. “We are happy that we never gave up. But the completion of the observatory is not the goal, but only the starting point.”

The world’s major infrared telescopes

(Name, operating countries, location, size of primary mirrors)

The Very Large Telescope (VLT), EU, Chile, four units of 8.1 meters each
Keck Telescope, the United States, Hawaii, two units of 10 meters each
The Large Binocular Telescope (LBT), the United States and other countries, Arizona, two objectives of 8.3 meters each
The Great Canary Telescope, Spain and other countries, Canary Islands in Spain, 10.4 meters
The South African Large Telescope, South Africa and other countries, South Africa, 9.2 meters
The Hobby-Eberly Telescope, the United States, Texas, 9.2 meters
The Subaru Telescope, Japan, Hawaii, 8.2 meters
The University of Tokyo Atacama Observatory (TAO), Japan, Chile, 6.5 meters
(Source: The National Astronomical Observatory of Japan’s data for 2024)