Arecibo Observatory has more science to do despite iconic radio telescope's collapse

The Arecibo Observatory in Puerto Rico, which collapsed in December 2020, is seen from space in this satellite image captured Feb. 23, 2021.
The Arecibo Observatory in Puerto Rico, which collapsed in December 2020, is seen from space in this satellite image captured Feb. 23, 2021. (Image credit: Maxar Technologies)

For decades, the words "Arecibo Observatory" was shorthand for the facility's massive radio telescope, one of those rare instruments that reached icon status  beyond its core science community.

But cable failures shattered the telescope and much of its vast dish last year, forcing the observatory to take stock of what science it can still do without the iconic telescope. In the months since the Puerto Rican telescope's fall, scientists at the site have rallied by looking ahead to the immediate future of research on site, using what instruments remain.

"Our focus has really shifted to a lot of these other pieces of equipment," Francisco Córdova, director of Arecibo Observatory, told "All of those have been operational throughout. Certainly they weren't the highlight of the site, but have been operational."

Related: Losing Arecibo Observatory would create a hole that can't be filled, scientists say

Unusually flexible scientific thinking has always been one of Arecibo's strengths. Although the massive radio dish was originally designed for atmospheric scientists to study the ionosphere, the facility blossomed to play a key role in two other scientific communities as well: radio astronomy and planetary science.

That history means Arecibo Observatory is used to hosting a range of research — even if its radio telescope commanded the spotlight — and has prepared the observatory to manage an eclectic research portfolio.

Arecibo and beyond

At Arecibo Observatory's main campus, nestled into the mountainous lush vegetation of Puerto Rico, scientists are rallying remaining instruments to carry on Arecibo's scientific legacy. Although the massive radio telescope dominated the site, it was hardly the only equipment to accumulate over the decades-long history of the observatory.

Prime among the other instruments available is a 39-foot (12 meters) radio antenna. It was originally brought to the site to simplify the main telescope's work on very-long-baseline interferometry, which otherwise required complicated steering maneuvers of massive equipment.

"Certainly now, as that becomes our main astronomy tool for a little while, we're shifting the priorities there," Córdova said. First on the agenda for the smaller dish, which is located on a hill overseeing the main telescope, is for it to join existing very-long-baseline interferometry networks on its own, since such collaborations magnify the power of individual instruments. Observatory staff are also hoping to add a cryogenic cooling system to the antenna so that the smaller telescope can do more meaningful research on its own.

Also available at the main Arecibo site are two lidar systems, or light detection and ranging systems. Such systems bounce lasers off (in this case) the atmosphere to better understand its ingredients and structure. One is being repaired as the observatory continues to recover from Hurricane Maria, which battered Puerto Rico in September 2017, but Córdova estimates it should be working normally by the end of the this year.

The facility's ionospheric heating systems are in a trickier state. Atmospheric scientists use such systems during week-long experiments that locally change the upper layer of Earth's atmosphere. For example, such systems can create so-called "artificial auroras" that resemble, but are much fainter than, the light shows created by charged particles slamming into molecules in the upper atmosphere. Scientists studying how the atmosphere responds to such events naturally, which can affect navigation and communication satellites, find experiments a helpful ancillary approach.

"They're very unique pieces of equipment," Córdova said. "They've been around for a while, but it's always been a science that's a niche. It's very unique and it's still not completely well understood, so there is a lot of opportunity."

The systems rely on antennas that were housed in the center of the massive radio dish; out of six antennas the observatory hosted, three are still standing. However, one incurred some damage, and the remaining antennas were a mismatched set. So once the antennas are safe to access, the observatory will need to move, repair and reset them.

"We feel that that is a capability that we could restore fairly quickly," Córdova said, noting that the precise timeline depends on how quickly personnel can clear away debris from the collapse. In addition, the system used to work with a device called an incoherent scatter radar, which was housed on the suspended platform above the radio dish and destroyed during the collapse and which the observatory can't fully mimic.

The observatory will also need to find a structure that will fill the role of reflector in the stead of the massive radio dish. "We're currently exploring different alternatives for what would be the right approach there," Córdova said. "We're trying to get a little bit creative with that aspect."

Related: Puerto Rican scientists mourn loss of Arecibo Observatory's iconic telescope

But the projects least impacted by the radio telescope's collapse are those not located near the now-destroyed dish. That includes those housed at what's known as the Remote Optical Facility, a fairly new facility located on the small island of Culebra, which lies about 17 miles (27 kilometers) east of Puerto Rico.

Right now, the main piece of equipment there is an all-sky camera that, along with another located at the main observatory site, keep an eye on whatever's happening overhead, all day long, which is unusual, Córdova said. "Our astronomy observations are typically very pointed," he said. "So this equipment is very interesting in the sense that it does give you the ability to do 24/7-type observations."

One phenomenon those all-sky cameras can spot are meteors entering Earth's atmosphere, and Arecibo plans to have a second instrument at the Culebra site to study such objects as well, this one a meteor radar system, a partnership with the University of Illinois. The equipment's arrival was coming to the site from Chile, a journey delayed by restrictions imposed to slow the coronavirus pandemic, but the observatory hopes to have the meteor radar system up later this year.

Radar is familiar territory for Arecibo Observatory; the radio telescope's planetary radar system was the most powerful in the world. But that system is no longer, and the meteor radar system will be quite different, Córdova emphasized. "[It's] nowhere near our old planetary radar, but it doesn't have to be, because the idea is that we're studying meteors as they are entering into the Earth's atmosphere, we don't want to go probe beyond that."

Before the radio telescope's collapse, a second instrument was also scheduled to join Culebra, this one a lidar device to study aerosols in the atmosphere, particularly the Saharan dust that billows across the Atlantic Ocean from Africa and can wash over the island. The new instrument will be able to parse out how high the dust and other aerosols are in the atmosphere, a relatively difficult measurement to make. "There are very few pieces of equipment that can be used to study that," Córdova said.

Turning the clock back

And then, of course, there's the task of managing the rich legacy of decades of observations by the lost radio telescope itself. First, the observatory is working on completing a project to bring together Arecibo data from the disparate locations where it's held to assemble one complete archive stored in the digital cloud, Córdova said. That project should be complete within a few months, he added.

Then, scientists are partnering with software engineers to develop automated algorithms to comb through old data looking for phenomena that were completely unknown when the telescope began work but are now commonplace.

"We've had a lot of recent discoveries that we didn't know existed 20 or 30 years ago, like FRBs and exoplanets," Córdova said, referring to the mysterious fast radio bursts that have puzzled astronomers for more than a decade. 

"Is there a possibility that there are a lot of those discoveries hidden in older data sets at Arecibo? Could somebody have picked up an FRB back in the '70s or the '80s or an exoplanet back in the '70s or the '80s and they never knew because they never really had the computing power?"

The observatory team also hopes that the algorithm work will eventually apply to another of the telescope's previous activities, studying the shape of near-Earth asteroids. Although scientists can work with the observations directly, one key product of planetary radar is a so-called shape model, which hones their understanding of an object's precise shape.

There's just one problem: producing a shape model takes at least six months, sometimes up to a year, far too long to keep up with Arecibo's lost planetary radar system. "In any given year, we would see with our planetary radar 100 different near-Earth objects and so if you can only map two of those it takes you kind of a while," Córdova said.

But for now, the team is working on the algorithm to detect fast radio bursts. Arecibo Telescope conducted its final survey for fast radio bursts in March 2020, Córdova said, and it took observatory scientists about nine months to dig through all the data that survey collected. An algorithm, so the hope goes, would speed that up — perhaps so significantly that scientists could gather follow-up observations guided by interesting data.

Then, it'll be time to do the same with exoplanets. As for how many such alien worlds could be lurking in old Arecibo data, Córdova said there's no way to know.

"We really don't have a clue, and that's one of those really cool things that everybody's a little bit excited about," he said. "There may be hundreds of these things out there we just didn't know all this time, or maybe it's one or two, we don't know."

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Meghan Bartels
Senior Writer

Meghan is a senior writer at and has more than five years' experience as a science journalist based in New York City. She joined in July 2018, with previous writing published in outlets including Newsweek and Audubon. Meghan earned an MA in science journalism from New York University and a BA in classics from Georgetown University, and in her free time she enjoys reading and visiting museums. Follow her on Twitter at @meghanbartels.