The world-famous Arecibo Observatory in Puerto Rico, known for helping scientists peer into deep space and listen for distant radio waves, is set to be decommissioned and demolished after engineers concluded that the facility’s structure is at risk of a collapse. While teams will try to salvage some parts of the observatory, the decommission will bring an end to the popular 57-year-old telescope, which has been featured in numerous films and television shows.

The decision comes after two major cables failed at the facility within the last few months, causing significant damage to the observatory. The National Science Foundation (NSF), which oversees Arecibo, assessed the impact of the cable breaks and found that the facility’s other cables could also fail soon. If some of the remaining cables break, engineers fear that the 900-ton suspended platform above the facility could come crashing down on Arecibo’s iconic 1,000-foot-wide dish. It’s also possible that three surrounding towers, which stand at more than 300 feet tall, could topple over in any direction, potentially hitting the visitor’s center or other important nearby buildings.

With this imminent threat in mind, NSF determined that Arecibo cannot be repaired safely without risking human life. The agency’s engineers have evacuated the facility and set up a safety exclusion zone around the spaces where people could be in danger if there was a collapse. Meanwhile, engineers are now working on a plan for how to take the facility apart safely, which could involve the use of helicopters and maybe even explosive demolitions. “This decision is not an easy one for NSF to make, but safety of people is our number one priority,” Sean Jones, the assistant director for the mathematical and physical sciences directorate at NSF, said during a call with reporters.

Arecibo Observatory has been a critical part of the science community for the last half-century, allowing scientists to observe exotic deep-space objects and events, such as pulsars and mysterious bursts of distant radio waves. Arecibo has also been a key tool in the search for asteroids that orbit near Earth, helping astronomers find objects that could potentially pose a threat to the planet. Additionally, scientists with the Search for Extraterrestrial Intelligence (SETI) have used Arecibo to search the sky for deep-space radio transmissions that could potentially come from intelligent worlds. Movie viewers will also recognize Arecibo from its inclusion in films like Goldeneye and Contact.

Image: UCF

The last few years haven’t been kind to Arecibo, though. In 2017, the facility suffered significant damage when Hurricane Maria passed over Puerto Rico, causing up to $14.3 million in needed repairs. Then in August of this year, an auxiliary cable, used to support the floating platform above the telescope, slipped out of its socket and fell, punching a hole in the observatory’s giant dish. At the time, the University of Central Florida, which manages Arecibo, halted observations with the telescope and launched an investigation, vowing to do repairs.

While engineers worked to get a replacement auxiliary cable, a second main cable snapped on November 6th, also falling onto the dish. The cable, which was attached to the same tower as the auxiliary cable that failed, caused additional damage to the structure and to nearby cables. Engineers with NSF did a full assessment of the facility after this second cable break and found that the remaining main cables, each weighing about 15,000 pounds, could not be relied upon. Arecibo’s main cables were installed decades ago, while the auxiliary cables were installed in the 1990s. “All of the main cables, all of which are decades old and have been through storms, earthquakes, and constant heavy moisture, may no longer be capable of supporting the load that they were designed [to carry],” Ashley Zauderer, the program director for the Arecibo Observatory at NSF, said during the call. In fact, the loss of just one more cable on one of the surrounding towers could lead to the uncontrolled collapse of the entire observatory.

Reports of an impending collapse surfaced soon after the second cable failure, but it wasn’t clear if the telescope could still be saved. Engineers don’t have a timeframe for when the collapse might happen, but they say that the facility will fall apart soon if no actions are taken — and there isn’t much that can be done to stop a collapse from taking place. “Even attempts of stabilization or testing the cables could result in accelerating the catastrophic failure,” Ralph Gaume, director of NSF’s division of astronomical sciences, said during the call. “Engineers cannot tell us the safety margin of the structure, but they have advised us that the structure will collapse in the near future on its own.”

NSF admits that while the agency was focused on other auxiliary cables slipping out of their sockets, no one had expected the main cable break — despite finding some evidence of weakening in the cable that failed. After the August cable failure, engineering teams began more frequent monitoring of Arecibo, and they noticed that 12 of the cable’s 160 wires had broken on the cable that failed. However, the engineers thought the cable was strong enough to handle these breaks and continue holding. “It was identified as an issue that needed to be addressed,” Zauderer said. “It was just not seen as an immediate threat, and I don’t think anyone understood that clearly the cable had deteriorated.”

Ultimately, NSF plans to take down the 900-ton platform and the giant dish in a controlled way, though the engineers don’t know exactly how long it will take or how much it will cost. And not all of Arecibo will be a total loss. NSF hopes to continue work at the Arecibo Observatory LIDAR facility eventually, as well as the visitor center. There is also an offsite facility on the island of Culebra, which collects data on clouds and rainfall. Analyses and cataloging of data collected by the Arecibo telescope will also continue for the foreseeable future.

Arecibo has been a beacon of opportunity in Puerto Rico, and plenty of scientists who have relied on the observatory over the years have expressed dismay at the idea that the telescope could be lost. While it’s a sad day for NSF, the agency is adamant that this was the best decision for the people who work at the observatory, and they are the most important assets. “I think it’s easy to say that it’s the telescope, but it’s not the telescope that’s the heart and soul [of the observatory], it’s the people,” Zauderer said. “NSF truly prioritized the safety of what is truly the treasure.”

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