SAN PEDRO DE ATACAMA, Chile — The road to the Chananto Plateau in northern Chile is rugged. In the Atacama Desert—the driest place on earth—the morning air is cold, asphalt roads are few and far between, and the dust clouds kicked up by heavy tires are annoying.

Suddenly, a huge, incongruous building appears out of the mist: we have reached the gateway to the world. Atacama Large Millimeter/Submillimeter Array (Alma), the tallest observatory in the world, security is so tight we might as well try to get into Area 51. The vast desert backdrop and the alien machinery perched atop these Andes mountains certainly add to the fantasy.

Located between 2,900 meters and 5,050 meters above sea level, Alma is the world’s largest astronomical project. It has 66 antennas, each as large as a five-story building, working together like a giant telescope to produce the deepest images of outer space.

It’s a unique setup: ALMA is an international project, with several countries vying to host the observatory, but Chile was chosen precisely because of this dry and remote location. Due to the altitude, the humidity in Chajnantor is usually only five percent (Typical UK household humidity is 50-55%).

“The conditions here allow us to reach far back into the early universe,” said Bill Dent, a systems astronomer who has worked at the Chilean site for 15 years. “But they are also harsh, and altitudes can be difficult on your body – especially for engineers who do the physical work of moving our antennas at more than 5,000 meters.”

Originally from the UK, Mr. Dent is one of 250 full-time employees in Chile. His team uses data captured by large antennas to study star and planet formation, deciphering secrets about the origins of Earth, the solar system and the wider galaxy.

“The best moments are when you get something unexpected,” Mr. Dent said I. One focus of his research is the phenomenon of debris disks in space: when dust and debris orbit a star, it forms visible rings around it. One night, while working alone, he noticed something unusual in an image from the antenna: “We detected gas around the star,” he explained, a clue that a new planet was forming. , about 450 light-years away. “Here is never seen before, looks great. I was thrilled to know that I was the first person on earth to know of its existence, and within a very short period of time. “

Working at such high altitudes is literally not for the faint of heart. Study shows long-term exposure can lead to chronic disease Examples include hypertrophy (enlargement of organs), hypoxia (lack of oxygen at the tissue level), and heart disease. Alma has strict safety rules and employees are required to undergo annual physicals that test things like blood pressure, nutrition and cardiovascular health. “But even the fittest and fittest people can experience nausea, fatigue, headaches and dizziness at this altitude,” Mr Dent said.

For example, exposure to lower oxygen levels and very dry air can lead to difficulty sleeping. “At an altitude of 5,000 meters, physical work and logical thinking are difficult without supplemental oxygen,” Mr Dent said. UV levels are also among the highest ever recorded on Earth, “so we have to be careful” to avoid sunburn, he added.

Today, many of the observatory’s astronomical activities take place at Alma’s Operations Support Facility (OSF), a huge climate-controlled building located 3,000 meters below sea level. Here, most of the team’s scientists can work or even stay overnight in on-site accommodation, although engineers are always required to be at the top site because ALMA’s antennas are placed and moved there every day.

The OSF building, littered with oversized bottles of sunscreen for public use, is a must-stop on the way to the top of Chajnantor. All employees and visitors must have their blood pressure checked here before being escorted up to 5,050 meters, and Chilean law requires that oxygen bottles be worn while driving and walking.

Alma is open 24 hours. Its antennas observe radio waves in space rather than visible light, so they don’t need to wait until dark to capture data. But scientists like Dent were working in the field during night shifts, monitoring equipment and choosing where and when to point antennas for optimal visibility.

Mr Dent explained that those working at top-level sites must acclimate to the OSF-level environment on the first day of the shift pattern. The next day they can work at altitudes above 3,000m for up to three hours, increasing to six hours at an altitude of 5,050m by the end of the week. Rest after a week, and sleeping at high altitudes is strictly prohibited.

It was early summer when we visited, with good visibility at the top and temperatures as high as -5°C, “although astronomers prefer it to be colder because warmer temperatures mean more water flows out of the ground, creating a small amount of water”. The humidity, that’s not good for visibility,” Mr Dent said.

This year he will leave Armagh after 15 years of service and return to the UK to enter semi-retirement. But he was one of several long-time employees who witnessed Alma’s early growth. How could this isolated desert oasis allow astronomers like him to work here for so long?

“There are still some big questions that remain unanswered,” he explains. “For example, understanding dark matter. One of the fundamental questions ALMA is studying is how did our galaxy form? Thanks to the images produced by our antenna, it is increasingly clear that most galaxies have black holes, and that these black holes formed the basis for the early universe Provides a seed in which galaxies form.

He added: “It would be fantastic to be able to observe planet formation processes in detail and, of course, detect evidence of life-sustaining atmospheres on Earth-like planets. It would be difficult to provide convincing evidence that they actually contain life. … But you never know.”