The large Cornell University-designed telescopic “ear” at Arecibo, Puerto Rico, which listened for the enlightening crackle of the cosmos for nearly six decades, now hears silence. 

In the wake of two recent support-cable failures, the National Science Foundation (NSF) will decommission and dismantle the giant dish at Arecibo Observatory — the world-class radio telescope in Puerto Rico that was conceived by Cornell faculty, built with federal funding and then managed by Cornell for its first five decades. 

The NSF announced the news Nov. 19. 

“Arecibo has been an incredibly productive facility for nearly 60 years,” said Jonathan Lunine, the David C. Duncan Professor in the Physical Sciences, and chair of the Department of Astronomy at Cornell University. 

“For the Cornell scientists and engineers who took a daring dream and realized it, for the scientists who made new discoveries with this uniquely powerful radio telescope and planetary radar,” Lunine said, “and for all the young people who were inspired to become scientists by the sight of this enormous telescope in the middle of the island of Puerto Rico, Arecibo’s end is an inestimable loss.” 

In August, a support cable detached and slashed the massive mesh dish, which measures 1,000 feet (305 meters) in diameter. The University of Central Florida, which now manages the facility on behalf of the NSF, sent engineers to evaluate fixing the famed telescope. 

Engineers had formulated solutions and were poised to implement emergency structural stabilization to the cable system that holds the dish, according to the NSF. But on Nov. 6, while awaiting delivery of replacement cables, a main cable snapped. 

Due to the stress on the second broken cable — which was thought to still be structurally sound — scientists at the NSF, which funds the facility, and engineers concluded that the remaining cables were likely weaker than originally believed. 

Conceived in the late 1950s by the late William E. Gordon, the Walter R. Reed Professor of Electrical Engineering at Cornell, Arecibo was a radar/radio telescope designed to study the Earth’s upper atmosphere and nearby space. The telescope was built in a natural bowl in central Puerto Rico in the early 1960s and became the world’s most powerful radio telescope and a key tool for astronomy, atmospheric science and planetary science. 

Like a gigantic ear attentive to the heavens, the Arecibo telescope had been Earth’s largest single-aperture radio telescope, tuned to find pulsars, galaxies and objects in the solar system and examine our planet’s ionosphere. It’s so large that the height of the Empire State Building fits in its diameter; the Washington Monument would sit snug at the dish’s focal point. 

The Arecibo listened day and night to the natural clatter throughout the universe. In 2012, the observatory captured one of the most fleeting, mysterious and rare deep-space events — a so-called “fast radio burst” that lasted a mere three one-thousandths of a second. 

“It was a single pulse,” said James Cordes, Cornell’s George Feldstein Professor of Astronomy and a prolific, enthusiastic patron. “The nature of these bursts had been in doubt…and the discovery at Arecibo cements the case that they are astrophysical.” 


Arecibo found the first pulsars in a binary system — a duet of neutron stars — in 1974, Cordes said. It mapped out water ice deposits in craters at the poles of Mercury, uncovered lake-like structures on the Saturnian moon Titan and measured the precise orbits of near-Earth asteroids. 

The discovery of the two pulsars in a binary orbit resulted in the confirmation of Albert Einstein’s prediction of the existence of gravitational waves, he said. This was the best evidence to their existence, until a direct detection of gravitational waves was made by LIGO in 2015. 

“My first trip to Arecibo was in 1972 as a first-year graduate student at the University of California, San Diego, working on pulsars,” Cordes said. “Over the years since, I’ve made about 150 trips to Puerto Rico and I’ve spent an accumulated total of three years there. 

“It was always a great thrill in the control room of the telescope,” Cordes said, “seeing pulses
from rotating neutron stars — pulsars — displayed on an oscilloscope in real time.” 

Forty-six years ago, Cornell astronomy professors Frank Drake and Carl Sagan famously sent a radio message via Arecibo to the heavens — featuring basic information about the human race — to potential extraterrestrials. The purpose was to call attention to the tremendous power of the newly installed radar transmitter at the observatory. 

“It was strictly a symbolic event, to show that we could do it,” said Donald Campbell, now a professor emeritus of astronomy (A&S), who was a research associate at the observatory at the time. 

Campbell went on to become director of the National Astronomy and Ionosphere Center, then based at Cornell, which managed the telescope until 2011 for the NSF. 

Arecibo was also the premier solar system radar facility in the world, and it was well funded by NASA to allow precise orbital motion studies of near-Earth asteroids, according to Campbell. “This is a big loss for tracking them,” he said. “Arecibo could determine the size, shape and rotation of near-Earth asteroids, and provide much more accurate predictions of their future orbits than can be obtained using optical telescopes alone.” 

Martha Haynes, the Goldwin Smith Professor of Astronomy at Cornell, first used Arecibo in 1973, when she was a summer research intern. She used Arecibo constantly. “Surveys of atomic hydrogen using Arecibo,” she said, “has been the cornerstone of my research career.” 

Haynes’ Arecibo work led to the discovery of the filamentary nature of the large-scale structure in the universe, which earned her the 1989 Henry Draper Medal from the National Academy of Sciences, an honor she shared with astronomy professor emeritus Riccardo Giovanelli. 

Currently, Cordes is part of a project called NANOGrav (the North American Nanohertz Observatory for Gravitational Waves), which uses pulsars as astrophysical clocks to detect gravitational waves from binary black holes. 

“In 15 years of obtaining data on this project, Arecibo contributed half,” Cordes said. “We were on the verge of making our first detection, so this is an especially terrible, major loss. Our project group, funded by the NSF, is now assessing how to deal with it.”