Eye on the sky — from Puerto Rico’s Arecibo Observatory | Discover

For five decades, one of the world’s most important radio telescopes, gathering essential information about outer space, has operated from Puerto Rico’s Arecibo, at the heart of the Caribbean, writes Erline Andrews

  • Opened in 1963, the radio telescope at Arecibo was the world’s largest for almost five decades. Photo by Dennis van de Water / Shutterstock.com

The Phaethon asteroid — a giant, globe-shaped rock more than three and a half miles across at its centre — orbits the sun just like the eight planets in our solar system. First sighted in 1983, it occasionally crosses paths with Earth. Because of its size and proximity to us, Phaethon is categorised as a “potentially hazardous asteroid,” or PHA, by NASA. If it ever hit the Earth, it could cause devastation beyond what we can imagine. And there are more than eight hundred other PHAs — that we know of.

Phaethon, named for the son of the god of the sun in Greek mythology, was last visible from Earth for a few days in mid-December last year, coming close enough to be seen even by amateurs’ telescopes. More important, it was also picked up by one of Earth’s most powerful telescopes, a bowl one thousand feet across, nestled in a sinkhole in the forests of Puerto Rico.

The images of Phaethon captured at the Arecibo Observatory revealed that the space rock has what may be a large crater at its equator, and is bigger than astronomers first thought. This is important information that we almost didn’t get. The Arecibo telescope suffered minor damage from Hurricane Maria, which had devastated Puerto Rico months earlier. The island was without electricity, and a shortage of diesel in the immediate aftermath meant there wasn’t enough fuel to operate the observatory’s generators, forcing a temporary shutdown of the telescope’s radar. It was back up and running just in time for Phaethon’s passage.

Arecibo’s radar operation is funded by NASA’s Near-Earth Object Observations Programme, which is part of the Planetary Defense Coordination Office, founded in 2016 to monitor and plan for possible asteroid impacts. “We are not in any imminent danger from anything as big as, say, what killed off the dinosaurs,” says Yan Fernandez, an astronomy professor at the University of Central Florida. “But there are plenty of things out there that are smaller than that. If they hit, there is a potential for serious problems and serious casualties.”

“Being able to understand the dynamics and the properties of these asteroids is going to help us understand the risks and potentially what could be done to prevent it,” Fernandez continues. “If you need to push an asteroid out of the way so that it won’t collide with Earth, that requires knowing something about what is the shape of the asteroid, what is the density, what is the interior like, what is it like on its surface. These are the kinds of things that Arecibo helps you understand.”


The Arecibo telescope has been around since 1963. It was the world’s largest single-dish telescope until 2016, when that position was taken by the FAST (Five-hundred-metre Aperture Spherical radio Telescope) in China. It was at Arecibo that scientists first detected gravitational waves, thus confirming Einstein’s theory of relativity. Physicists Russell Hulse and Joseph Taylor were awarded the 1993 Nobel Prize for their discovery. The first planets outside our solar system — called exoplanets — were discovered at Arecibo in 1992. Hundreds of scientists all over the world use data collected from the telescope to conduct research on outer space, and the Earth’s own upper atmosphere as well.

“Arecibo is a great place to do atmospheric science,” says Fernandez. “In a time when global climate change is happening, with the possibility of having more and stronger hurricanes coming in the future, having a much better idea about what the atmosphere is like is really important for understanding what the future might be like on planet Earth.”

And in case human beings one day have to look for another planet to live on, data from the observatory is used by the Planetary Habitability Laboratory at the University of Puerto Rico. The PHL maintains a Habitable Exoplanets Catalogue, which now has fifty-three candidates. “We are trying to observe red dwarf stars,” says PHL director Abel Mendez, referring to stars that can’t be seen with the naked eye. “They are the most abundant type of stars. Many of the potentially habitable worlds that have been found are around those stars.”

In 1974, a team of scientists sent what became known as the Arecibo Message from the observatory. It was coded in the form of radio waves, and had as its target a distant cluster of stars. The very slim hope is that it could be picked up by intelligent life. 

Today the Search for Extraterrestrial Intelligence (SETI) movement continues in the form of SETI@Home, run by scientists at the University of California, Berkeley. The programme, started in 1999, uses millions of computer users all over the world to look for anything unusual in radio emissions coming from space. And the data are collected at Arecibo. 

“SETI@Home has a history of catching the public’s imagination,” says director Eric Korpela. “When we first started out, we expected to get ten thousand people, and in the first two weeks two million people signed up. The question ‘Are we alone in the universe?’ is one of the most profound things that we can ask ourselves.”

Considering the telescope’s importance, it’s hard to imagine there’s been talk of shuttering it. The National Science Foundation, which provides most of the funding for the observatory, had been struggling for years to continue doing so. In December, a three-way consortium led by the University of Central Florida won a competitive bidding process to take over the operation and part financing of the observatory for the next five years. After a transition period, the new management began on 1 April this year.

Professor Fernandez is UCF’s main representative at the observatory. The on-the-ground management of the observatory has not changed, nor has much else. “Our overarching goal,” Fernandez says of the management shift, “was for everyone to keep doing the great things they’d already been doing.” 

Fernandez believes the Arecibo telescope — which also has a place in pop culture through key appearances in the movies Contact and GoldenEye and the TV show The X-Files — is worth the US$20 million cost of the management deal. Despite the size advantage of China’s FAST, Fernandez says, “Arecibo is the most powerful single dish telescope in the world.”

“Even though it’s a fifty-year-old facility, the superlatives are still there,” he says. “There are capabilities there in terms of astronomy, planetary science, atmospheric science, and earth science that you just cannot do anywhere else in the world.”

Funding provided by the 11th EDF Regional Private Sector Development Programme Direct Support Grants Programme.
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