SANTIAGO – After decades of planning, construction of the world’s largest optical and infrared telescope is set to start later this month on a mountain in the middle of Atacama desert, in northern Chile.
With a lens diameter of 39 metres, the Extremely Large Telescope (ELT) is set to become “the biggest eye” available for sky observation from Earth. It is expected to improve efforts to search for potentially habitable planets or research dark matter and black holes.
This project is led by the European Southern Observatory (ESO), a consortium bringing together 15 European countries and Brazil. The organization also operates other major telescopes in Chile, such as the ALMA interferometer and the Very Large Telescope (VLT).
The site for the new ELT is Cerro Armazones, a mountain some 130 kilometres south of the Chilean city of Antofagasta. Two years ago, the top of the mountain was flattened so it could host this ambitious work of engineering: an 80-metre dome with a mirror that will rotate to follow the movement of the stars.
Construction is set to begin on May 26, and the telescope is expected to be operational – or, as astronomers put it, to see first light – in November 2024.
“The leap between the telescopes we currently have and the ELT is almost as large as the leap between Galileo’s naked eye and his telescope,” ESO director general Tim de Zeeuw recently told DPA in Madrid.
The ELT’s mirror is set to be five times larger than those in the most advanced telescopes that are currently operational. It will also be able to gather 13 times more light than today’s top telescopes, making its images much clearer.
One of the goals of the ELT is to search for planets where life may be possible beyond the Solar System, including the recently discovered Trappist-1 and Proxima b systems. The ELT’s size will enable larger images, and perhaps even direct measurements of the properties of those planets’ atmospheres.
With technology like this, De Zeeuw says, the first habitable planet beyond the Solar System could be discovered within a decade.
“It’s odd that this telescope can help us find evidence of life in other planets, from one of the world’s most inhospitable places, the Atacama desert,” De Zeeuw says.
The Atacama is, indeed, one of the driest places on Earth. Parts of the 105,000 square kilometre desert have never seen rainfall since record-keeping began.
The area is also perfect for observing space. Nearby, the Humboldt Current, a cold ocean current, ensures that clouds stay over the Pacific, or on the other side of the Andes, so night skies remain generally clear.
When constructed, the ELT will have a total of five mirrors. The largest of them, the telescope’s 39-metre primary mirror, will be made up of almost 800 hexagonal segments, each of them with a 1.4-metre diameter, which must fit together perfectly.
“No one knows how to make a mirror that size in one piece. And even if anyone could, it would be impossible to transport,” De Zeeuw explains.
De Zeeuw, a soft-spoken Dutch astronomer, helped to secure the 1.1 billion euros (1.2 billion dollars) needed to finance the ELT from mainly European donors. In the recent phase of austerity, that was “a very interesting exercise,” he admits.
The ELT was first envisaged in the late 1990s, when the ESO looked into whether a telescope could be built with a 100-metre diameter. Building such a device would cost somewhere between 3 billion and 4 billion euros, they found, so its dimensions were reduced to a 39-metre diameter.
And yet, the ELT is not the only current project for a massive telescope. In the United States, a competition for public funds is ongoing between Caltech’s Thirty Metre Telescope, set to be located in Hawaii, and the Carnegie Science Centre’s Giant Magellan Telescope, also to be built in Chile.
“Early in the 21st century, there were also two initial projects in Europe, but my predecessor convinced everyone that we had to work together,” De Zeeuw says.
The Dutch expert believes that having several giant telescopes will be a good thing, as it will ensure high-level research in both the northern and southern hemispheres.
“Competing with someone else makes you better. You need to be faster and better. That is good for everyone,” he says.