Damage at the Arecibo Observatory after one of the main cables holding the receiver broke in Arecibo, Puerto Rico

At 8 a.m. on 1 December, the Arecibo telescope’s instrument platform crashed into the dish below, tearing more gashes into an already damaged structure.Credit: Ricardo Arduengo/AFP via Getty

The iconic radio telescope at the Arecibo Observatory in Puerto Rico has collapsed, leaving astronomers and the Puerto Rican scientific community to mourn its demise.

Engineers had warned that the 900-tonne platform suspended above the telescope’s 305-metre-wide dish could fall at any moment, given that one of the main cables supporting it had snapped in early November. Last month, the US National Science Foundation (NSF), which owns the observatory, had announced it would shut down the telescope permanently, citing safety concerns over its instability, and damage too extensive to repair.

Damage at the Arecibo Observatory after one of the main cables holding the receiver broke in Arecibo, Puerto Rico

This close-up view of the smashed instrument platform shows the holes it left in the telescope’s dish, which is nestled in a crater in the mountains of Puerto Rico.Credit: Ricardo Arduengo/AFP via Getty

The final collapse happened just before 8 a.m. local time on 1 December. No one was injured.

Drone footage of the collapse, released by the NSF two days later, shows cables snapping at the top of one of the three towers from which the instrument platform was suspended. The platform plummets downward and crashes into the side of the dish. The tops of all three towers also snap off.

This video, taken by an observatory drone and released by the NSF on 3 December, shows the telescope's instrument platform fall and crash into the side of the dish.

Prior to the failure, engineers had been exploring options to relieve some of the tension in the cables, including by relaxing other support cables to tilt the towers around the dish. The NSF had not yet decided to move forward with that plan when the platform collapsed.

Some nearby buildings, including the control room and the visitor centre, survived the collapse. An educational centre, however, seems to have been substantially damaged by the falling platform and cables.

Questions remain about whether the cables were maintained properly over the years. The cable that failed in November, precipitating the final collapse, dated back to the observatory’s construction in 1963.

The Arecibo radio telescope in Puerto Rico before the destruction of the telescope in 2020

Before its collapse, the 900-tonne instrument platform hung 130 metres above the Arecibo telescope’s dish, suspended by cables strung from three towers.Credit: Dr Seth Shostak/Science Photo Library

Once the world’s largest single-dish radio telescope, the Arecibo facility has been the site of many key astronomical discoveries over the years, including observations of the spinning stars known as pulsars that led to the 1993 Nobel Prize in Physics. Before its collapse, astronomers were using the telescope for a number of scientific studies, including radar assessments of near-Earth asteroids, to measure their threat to the planet.

“Our hearts are heavy about this,” said Thomas Zurbuchen, NASA’s associate administrator for science, at a 1 December NASA advisory meeting.

The NSF says it will continue paying staff at the observatory and carry on with science at other, smaller facilities on site that do not involve the 305-metre dish. It is unclear whether the dish will be demolished, rebuilt or left in ruins, as-is. Observatory director Francisco Córdova told reporters that officials would investigate ways of establishing similar or even better scientific capabilities, perhaps at or near the site. This would, however, depend on the US Congress allocating money to replace the Arecibo dish.

Ralph Gaume, the head of NSF's astronomy division, said at a 3 December press briefing that any replacement would be a multi-year process involving congressional funding and assessment of the scientific community's needs.