Europe Levelled a Mountain to Build a $1BN Telescope

Video hosted and narrated by Fred Mills. This video contains paid promotion for Brilliant.

IT’S a construction project that’s truly out of this world.

In the middle of a desert, and on top of a mountain, the largest optical telescope on Earth is coming together.

Almost the height of Big Ben, it will produce images of far-away planets that are 15 times sharper than NASA’s Hubble Space Telescope. 

And it’s required 16 nations to partner on it; otherwise it would be impossible to achieve.

But how do you build an Extremely Large Telescope in one of the most remote locations on Earth, and how much will this advance our understanding of the universe?

Above: It's easy to see how the Extremely Large Telescope (ELT) got its name.

Stretching for around 1,000 kilometres along the Pacific Coast of South America is Chile’s Atacama Desert. 

It’s the driest place on Earth, outside of Antarctica. There are volcanoes, salt flats and a whole lot of dust — features that make it look like a scene from an alien planet. After all, this is where the European Space Agency likes to test its Mars rovers.

And it just so happens that here, 3,000 metres above sea level and 150 kilometres from the nearest city, is a site that will give humanity a better view of other worlds than ever before.

Having it large

On this very spot, ESO, the European Southern Observatory, is building what they’ve cleverly called the Extremely Large Telescope, or ELT for short.

39 metres wide, its primary mirror is four times bigger than the ones found in the current largest telescopes of this kind.

Oh, and it’s just one of five mirrors that make up the whole thing. Without getting too technical, we’ll explain how all of that works later.

Above: The enormous main mirror allows the ELT to gather 100 million times more light than the human eye. Image courtesy of ESO/L. Calçada

To give all of this high-tech kit protection from the elements, everything will be contained inside a giant steel dome covered in insulated cladding and weighing over 6,000 tonnes.

Underneath, 36 trolleys are attached to the circular concrete pier on which the telescope sits. These let the telescope turn 360 degrees.

So, how did the construction teams even begin to build something so complex in the middle of this barren landscape, hours from civilisation?

Picking the location

Well, before they could do any work at all, ESO had to find the perfect place to put it. Sites were also considered in Spain, Morocco and Argentina, so why here?

“The very important and fundamental aspect was a location that could allow the fulfilment and the investigation of the scientific goal of the telescope,” explained Roberto Tamai, programme manager for the ELT project at ESO. It’s one of the leading intergovernmental organisations in astronomy, with 16 member states. 

According to Roberto there were many factors involved in the decision to pick this particular mountain.

“The turbulence and the content of water vapour, the content of wind, rain. Think about constructing such a big telescope in a location where 50% of the time you need to keep the door closed because it's raining,” he said.

Above: The Atacama Desert is the perfect location for the new telescope. Image courtesy of ESO/NVP3D.

Other things to consider included ground conditions, altitude, whether there’s any light pollution, and how clear and dark the skies are. The Atacama ticked all the boxes.

In 2010, after many months of testing and analysing data from various sites they agreed on a location — the peak of the Cerro Armazones mountain.

But there was a problem. Mountains are pointy, and the telescope needed a flat, level surface on which to build. The solution? Cut the top off.

Off with its head

Yes, that’s right. To enable construction to begin, the summit was flattened in 2014.

This was done by drilling big holes, filling them with explosives and lighting the fuse. Then, the rubble was swept away and a road was put in so vehicles could actually reach the site.

Above: The result of the flattening process. Image courtesy of M. Struik (CERN)/ESO.

And yet, this was only the start of the preparations, and problems were already emerging.

“Unfortunately, while digging there we realised that the half of the mountain, at the centre, was a lot of fractured rock and sand, and as I'm sure you understand it is not good to put a foundation on sand,” Tamai revealed.

Partly due to this, it wasn’t until 2019 that the foundations, and the outline of the structure, began to take shape.

The material of the surface was not the only issue, though; this is one of the world’s most seismically active regions.

On firm footing

To stop the many fragile parts from being damaged in an earthquake, the ELT rests on a concrete base that’s separated from the ground.

Inside the gap in between, isolators have been put in, which absorb lateral and vertical forces in the event of a quake.

By 2023 it was time to start on the dome. This is made up of steel segments weighing as much as 70 tonnes each.

How did they get these chunks of metal up the mountain? Well, they started off as individual steel beams that were joined together at a base camp nearby.

Next, they were put on the back of these remote-controlled transporters, which carried them to the summit.

Above: Once the pieces were at the top the cranes took over, assembling the exterior like an oversized Lego set. Image courtesy of ESO.

As for how the components got to this whole area in the first place, a lot of the infrastructure was already in place.

You see, just over 20km away from here is one of ESO’s other stargazing sites — the Very Large Telescope, or VLT.

Before this was built, roads, utilities and everything else needed to run a science facility had to be constructed first.

That meant all they had to do was build extensions to ELT, which still isn’t easy but it’s a whole lot simpler than building it all from scratch.

How big is TOO big?

Now, we know what you’re thinking. They’ve already built the Very Large Telescope, and the Extremely Large Telescope is now under construction. Surely it’s only a matter of time before the Ridiculously Massive Telescope — or something like it — comes along?

While there’s obviously a chance that a bigger one is built at some point, right now the ELT is as large as things can get.

Why? It’s to do with the mirrors. 39 metres is about as big as it’s possible to go while remaining cost-effective.

ESO knows all about that; they already tried to make one with a 100-metre mirror. But it had to be cancelled because it would’ve been too complex and expensive. What was it called? The Overwhelmingly Large Telescope. No, seriously.

Above: The Overwhelmingly Large Telescope proved to be a step too far. Image courtesy of ESO. 

Anyway, back to the Extremely Large Telescope and we’re still in 2023 — the year the project officially reached the halfway stage.

As well as the framework for the dome, the support cell — a large lattice structure that will eventually hold the main mirror — began coming together inside. Like everything else with this project, it’s gigantic. 

So, now is probably a good time to talk about those mirrors, which are nothing like the kind we all use on a daily basis.

These ones are much bigger and more sophisticated, have different shapes, sizes and roles, and all combine seamlessly to make the telescope actually work.

All done with mirrors

M1 — the main mirror — is the biggest of the lot and consists of almost 800 hexagonal segments. 

Its job is to gather the light from space and reflect it up to the second mirror — M2 — hanging above it. Light is then sent down to M3 before it goes back up to M4. 

This mirror can correct any distortions caused by atmospheric turbulence. It does this by activating a set of powerful lasers.

These are fired into the sky to make artificial guide stars for the telescope to see. 

They allow the ELT to measure blurring in the atmosphere, which can then be corrected by this mirror. This is called active optics and it’s already in use on the VLT.

Above: A rendering of the finished ELT and its active optics system. Image courtesy of ESO.

Still with us? Good. After it’s passed through M4, the light is directed through to M5. 

Here is where the image is stabilised before it reaches the various instruments for processing. 

But enough about mirrors. Now it’s time for the really big question — what is ESO hoping to achieve with this device?

Setting sights high

In short, something incredible. ELT will be the only telescope capable of taking direct images of rocky exoplanets outside our solar system — ones that might be able to sustain life.

Right now, we’re only able to see them indirectly — when a planet passes in front of a star, for example.

“We will be able to understand if the atmosphere around those planets allow life as we know it,” Tamai said. 

“So, there would be chlorophyll, there would be water, CO2, pollution — if there is anybody that is making pollution, as we are doing on Earth. So, it will be extremely powerful.”

Such a large light-collecting area will also allow it to look much deeper into the universe and help discover more about its origins and the mysteries of dark matter and dark energy.

Above: With the ELT, scientists will be able to observe extrasolar planets directly for the first time.

Another thing we should point out is that while the ELT will be huge, it won’t be the biggest telescope overall.

If you’ve seen Goldeneye, you’ll know that radio telescopes, which have a dish instead of mirrors, can be a lot larger.

But they’re different; instead of visible light, they detect radio waves. In other words, they listen; optical telescopes observe. Plus, optical ones look cooler, and they have lasers.

Big spenders

Final question — how much is it costing and who is paying? Well, the total is expected to be around USD 1.6BN. 

Funding has come from those 16 member states, which have made various contributions depending on their size.

“Those member states are the governments that are putting the money in the organisation. There are member states that are putting in more money because they are bigger and member states putting in less money because they're smaller,” explained Tamai.

“No single member state alone would have been capable of putting in so much funding, so much money, for a scientific project.”

Splitting the bill in this way doesn’t just make sense financially; those countries will all benefit from the results of the project too.

After all, the discoveries the ELT will make when it completes by the end of the decade could affect all of us.

For centuries we’ve been wondering whether we’re truly alone in the universe. This may just give us the answer we’ve been waiting for.

Above: The project couldn't have been achieved without multiple countries contributing. Image courtesy of G. Hüdepohl (atacamaphoto.com)/ESO.

The Extremely Large Telescope is an astronomical construction project, in every sense of the word. 

The scale is extraordinary, the location is breathtaking and the scientific, technological and logistical challenges required to make this happen are simply astounding.

And when you consider the job it’s going to need to do when finished as well, there’s no denying this particular mega-build is in a world of its own.

This video and article contain paid promotion for Brilliant. To try everything Brilliant has to offer for free for a full 30 days, visit https://brilliant.org/TheB1M/ you’ll also get 20% off an annual premium subscription.

Video narrated and hosted by Fred Mills. Special thanks to the European Southern Observatory (ESO). Additional footage and images courtesy of ESO, ACe Consortium, Amblin Entertainment, B. Häußler, Cimolai, Dreamworks, E. Sech, A. Dradi, G. Hüdepohl (atacamaphoto.com), Gramercy Pictures, G. Vecchia, L. Calçada, MGM/UA, MICADO Consortium, Misfile, Safran, Samuel Santana Schudi, Sony, 20th Century Fox, 20th Century Studios, Walt Disney Pictures and Warner Bros. Pictures.

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