When the Arecibo telescope collapsed, the world lost a powerful asteroid tracker and alien seeker

Video footage showed Arecibo's enormous hanging platform crashing into the dish below on Tuesday morning.

—Morgan McFall-Johnsen (@MorganMJohnsen) December 3, 2020

 

"As you can see, this was a very violent and kind of unpredictable failure," Ashley Zauderer, the NSF program manager for the Arecibo Observatory, said in a briefing on Thursday.

Two cable failures in August and November had weakened the structure. That put extra weight on the remaining cables until they snapped, too.

The area around the dish and the three towers had been cordoned off well before the collapse, since operators were already aware of the risk. So nobody was injured, according to the NSF.

The loss of Arecibo is a major blow to the world's defenses against hazardous asteroids.

Arecibo didn't discover dangerous space rocks, but it was instrumental in investigating them, Mendez said: The observatory could ping such objects with radar to decrypt their shape, rotation, surface features, and trajectory through space.

Arecibo was also the best shot the US had at a comprehensive project to search for radio waves from alien technology.

With its demise, that possibility dies, Mendez said.

Other NSF facilities, like the Green Bank Observatory in West Virginia, could take on some Arecibo science. But Mendez said Green Bank is only 10% to 20% as sensitive to weak radio signals as Arecibo was.

The telescope was the brainchild of Cornell University professor William E. Gordon, who began designing it in 1958.

He wanted to use radar to study the ionosphere: a layer of electrons in Earth's upper atmosphere that interacts with particles in space to create the aurora.

He chose a natural sinkhole in Puerto Rico, where the terrain would fit the telescope's deep, 1,000-foot-wide dish.

Building the observatory close to the equator would also make it easier to study nearby planets.

Construction began in the summer of 1960. Building the world's largest radio telescope was no easy feat.

"I do not know how we ever built it," Gordon later told a gathering at the observatory in 2003.

He added that the telescope was only designed to last 10 years, but said he hoped it would live another 40.

In 1963, the dish was completed with the reflection platform raised above it, supported by 18 cables connected to three towers.

"A big cheer went up when it was completed," Gordon said.

After that Arecibo's massive dish antennae began to ping celestial objects by reflecting radio waves from space to its suspended platform.

The telescope started to observe the cosmos. Its first major discovery was that scientists had Mercury's rotation all wrong.

Astronomers previously thought that Mercury rotated every 88 days, but Arecibo found that it was actually every 59 days. The telescope also showed that the planet is not tidally locked with the sun, as astronomers previously believed.

Then in 1974 it detected the first ever binary pulsar: a highly magnetized, compact star orbiting another star. This was a confirmation of Einstein's theory of general relativity.

The physicists behind the discovery, Russell Hulse and Joseph Taylor, later won the Nobel Prize in Physics.

That same year, Arecibo beamed the most powerful broadcast Earth has ever sent to communicate with potential aliens.

The message contained information about the basic chemicals of life on Earth, the building blocks and shape of our DNA, the human figure, a map of our solar system, and a description of Arecibo itself.

Its radar made the first maps of Venus's surface in 1981.

Previously, optical observations of the planet could only show the thick haze of clouds in its atmosphere.

In 1992, Arecibo discovered the first known planet beyond our solar system.

Later observations revealed an entire planetary system orbiting a pulsar.

The telescope made appearances in the 1995 James Bond film "GoldenEye" and the 1997 film "Contact."

Arecibo was visually striking due to both its size and its jungle setting.

In 1997, the observatory got its Gregorian Dome.

The technology focuses the telescope's radiation to the points in space that astronomers want to study.

Arecibo identified the world's first repeating fast radio burst - millisecond pulses of radio from beyond our galaxy.

Some astronomers thought these signals could come from alien technology. But more recent discoveries indicate that dead stars produce the bursts.

Arecibo's woes began in August, shortly after Tropical Storm Isaias passed over Puerto Rico. An auxiliary cable broke and crashed into the dish below.

It tore a 100-foot gash in the reflector dish.

Three months later, just before engineers were set to begin repairs, a 15,000-pound main cable broke from the same tower and crashed into the dish.

Astronomers began to worry seriously about the telescope's fate.

"Its sensitivity is so much greater than any other instrument and it's so much more flexible," Joanna Rankin, a radio astronomer at the University of Vermont, told Science after the second failure, adding that Arecibo can see "from the stratosphere to the far reaches of the universe."

"It would be a tremendous shame if that was lost," she said.

Then assessments engineers warned that if another cable were to break from the same tower, that could send the 900-ton platform plummeting into the dish below. It would bring all three towers with it.

The new break had shown that the remaining cables were no longer reliable. That meant a collapse could happen at anytime, which made it unsafe for engineers to attempt to stabilize or repair the telescope.

So the NSF decommissioned the telescope, and engineers set about figuring out how to deconstruct it safely.

"This decision is not an easy one for NSF to make. But safety of people is our No. 1 priority," Sean Jones, the assistant director for the NSF's Mathematical and Physical Sciences directorate, said in a press conference on November 19.

Over the past two decades, the NSF has spent more than $200 million operating and maintaining the observatory.

If engineers had succeeded in taking apart the telescope before it collapsed, the foundation would have had a better shot at preserving the visitor's center and nearby lidar facilities.

But before they could make an attempt at taking it apart, the platform collapsed.

"I feel sick in my stomach," Ramon Lugo, the director of the Florida Space Institute at the University of Central Florida, who managed the telescope, told Science on Tuesday. "Truthfully, it was a lot of hard work by a lot of people trying to restore this facility. It's disappointing we weren't successful. It's really a hard morning."

The only radio telescope on Earth that can hold a candle to Arecibo is China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST).

"If you are monitoring a source of interest which is in the weak radio spectrum, you need two big radio telescopes: one pointing toward something during the day and the other through the nighttime," Mendez said. "If you lose Arecibo, then you lose the ability to monitor — 24 hours a day — a faint source of radio signals."

He added: "Now we just have one eye."

Already, astronomers are sharing ideas for building a state-of-the-art facility in Arecibo's place.

This would require the incoming Biden administration to push for such an effort and Congress to fund it.

"A rebuilt Arecibo would be an important scientific instrument in many realms, notably gravitational waves," Saavik Ford, an astrophysicist at the City University of New York and the American Museum of Natural History, wrote to an astronomy email list before the observatory's downfall.

She added: "Rebuilding is a choice which would yield both economic benefits and (importantly) scientific advances."

This story has been updated with new information and footage. It was originally published on December 2, 2020.

Dave Mosher and Aylin Woodward contributed reporting.