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The second-largest radio telescope in the world is shutting down

The Arecibo Observatory's 1000-foot-wide telescope in Puerto Rico can’t be repaired without putting crews under enormous risk.
November 19, 2020
arecibo broken cable
arecibo broken cable
A view of the damage caused to Arecibo's radio telescope in August.UCF

The US National Science Foundation has just announced it is going to begin decommissioning the famous Arecibo Observatory, the 1,000-foot-wide, 900-ton radio telescope located in Puerto Rico. It’s a huge blow to the astronomy community, which used Arecibo for 57 years to conduct an enormous amount of space and atmospheric research. 

What happened: Arecibo has withstood decades of wear and tear from various storms and other natural disasters, including damage by Hurricane Maria in 2017 and a few earthquakes in January. But in August, a support cable slipped out of its socket and caused a 100-foot-long tear in the dish. Engineers deemed the problem stable and reparable, but a second cable outright snapped on November 6. This new cable had been connected to the same tower as the previous one: after dealing with the extra weight on its own for several months, it finally broke. 

Engineer evaluations of the damage found that the structure is “in danger of a catastrophic failure” and the telescope could collapse at any moment. The NSF (which oversees the telescope) decided trying to repair Arecibo would be too dangerous for construction workers and staff. Even if the repairs were successful, there would be no way to guarantee long-term stability. 

Legacy cut short: For most of its life, Arecibo was the largest single-dish radio telescope in the world (a status surpassed in 2016 with the completion of China’s Five-hundred-meter Aperture Spherical Telescope, or FAST). For decades, Arecibo was uniquely capable of studying the atmosphere and objects in space in ways no other instruments could, especially when it came to making radar observations of distant planets, moons, and near-Earth asteroids. Arecibo is one of the few facilities on the planet that can blast radar beams to objects in the solar system and successfully pick up a bounce back that could be used to ascertain the structure and movement of those objects. 

Some of its most notable achievements were finding evidence for the existence of neutron stars, directly imaging an asteroid for the first time in history, and detecting a pulsar that was home to the first exoplanets ever identified

It also played a huge role in popularizing the search for extraterrestrial intelligence (SETI). In 1974, scientists used Arecibo to fire off the Arecibo message, a 1,679-bit interstellar radio message directed toward globular star cluster M13 (21,000 light-years away) to communicate with any intelligent life that might be there. 

What’s next: To be fair, Arecibo’s significance has waned in recent years with the rise of newer facilities, especially FAST. Its decommission will create a hole in radio astronomy, but many other instruments should be able to pick up where Arecibo left off. And the NSF’s decommissioning plan only extends to the 1,000-foot-wide telescope. Other parts of the observatory will remain intact, such as the lidar facility that’s important to studying space weather and magnetosphere interactions. 

Correction: We changed the units for the telescope's width.

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Illustration by Rose WongIllustration by Rose Wong

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