Astronomers Are Mourning The Decision To Close Arecibo Observatory

The Arecibo telescope in happier times. The observatory was for more than 50 years the largerst radio receiver in the world. JidoBG CC-By-4.0

The American National Science Foundation (NSF) has announced its intention to demolish the giant Arecibo Observatory, which for many years was the largest telescope in the world. The decision has nevertheless unleashed a torrent of online regret. Not only was Arecibo the site of decades of important research but it also stood as a symbol of astronomy as a whole. A last-ditch campaign is being mounted to persuade Congress to fund the repair directly, but most observers are pessimistic.

The 305-meter (1,000-foot) Arecibo telescope was opened in 1963, occupying a sinkhole in northern Puerto Rico. Until the construction of China's 500-meter (1,640-foot) Aperture Spherical Telescope (FAST), it was the largest single-dish telescope in the world. Arecibo contributed to almost every area of astronomy, with highlights including confirmation of neutron stars, the rotation of Mercury, the first pulsar to be found to have planets, and the search for extraterrestrial life. It also sent humanity's largest signal beamed in the slim hope aliens might find us, an action some condemned as foolhardy. If a civilization in the M13 globular cluster has a receiver the size of Arecibo, they may learn of our presence in 21,000 years.

The immense size of the dish has seen it used in a Bond film as well as the more intuitive Contact and the X-Files.

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Increasing maintenance costs and budget squeezes have seen the observatory's future imperiled several times, but the beginning of the end came in August when a snapped cable ripped a 30-meter (100-foot) gash in the reflector dish. The (apparently) final straw came last week when a second cable from the same support tower broke.

The NSF is concerned tests of the strength of remaining cables would place workers at risk. “In the end, a preponderance of data showed that we simply could not do this safely. And that is a line we cannot cross,” the NSF's Ralph Gaume said in a statement. Others dispute this, but even if a safe path can be found, the money may not be there to make it happen.

Despite the arrival of radio telescope arrays, the opening of the FAST shows there is still demand for big dishes.

Although a fleet of giant new optical telescopes are under construction and the Square Kilometer Array will be far more powerful than Aricebo could ever be, no telescope in the world can currently replace Arecibo's capacity for radar mapping asteroids and other planets. Even for functions where they can match Arecibo, other telescopes are over-booked so projects with time scheduled on the giant dish may wait years before they can get their data.

Arecibo's loss will also be a blow to Puerto Rico. The island's economy was in poor shape even before Hurricane Maria caused the deaths of 3,000 people and led to mass emigration. The observatory created employment and attracted tourists.

Not all the news is bad for historic telescopes, however. In the same month as Arecibo had the first cable break, the Lick Observatory was threatened by California's fires. In the end, thanks to lucky winds and the heroic efforts of local firefighters, the facility made it through. Soon after fires reached one of the support buildings of another iconic California telescope at Mount Wilson. Not only did the observatory survive but it also became a temporary sanctuary for a bear burned out of its usual habitat.

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