Astronomy Now - January 2021

T

Arecibo collapses after suffering

catastrophic damage

he famous Arecibo radio telescope in Puerto Rico has collapsed after the cables holding the

instrument platform aloft, 137 metres over the telescope’s bowl-shaped dish, broke, allowing the

platform to plummet to its doom.

e telescope had been closed since 10 August 2020 qhen an auxiliary cable broke and swung down,

tearing a large hole in the dish (see When telescopes fall down, AN, October 2020). en, on 6

November, one of the main cables holding the platform broke away. Engineering consultancy rm

ornton Tomasetti assessed the damage, nding that the main cable broke despite being only at 60

per cent of its minimum breaking strength, and that almost all the other cables were showing signs

of fatigue. Given the dangers that engineers would face in repairing the cables, ornton Tomasetti

recommended that Arecibo be decommissioned, an assessment that other independent engineering

consultants mostly agreed with.

Protests were raised by some scientists desperate to keep Arecibo open, but it was all in vain. On the

morning of 1 December the other cables gave way, shearing off the top sections of all three towers

supporting them, and the 816 metric tonne instrumentation platform fell into the dish, smashing it

to pieces.

“We are saddened by this situation but thankful that no one was hurt,” says Sethuraman

Panchanathan, Director of the National Science Foundation (NSF), which co-funded and managed

Arecibo along with the University of Central Florida. “Our focus is now on assessing the damage,

nding ways to restore operations at other parts of the observatory, and working to continue

supporting the scientic community and the people of Puerto Rico.”

Prior to the collapse, plans were in place for Arecibo to receive a next generation multi-beam

receiver. However, Ralph Gaume, Director of the NSF’s Division of Astronomical Sciences is

adament that the observatory will not be shut down. e NSF plans to keep Arecibo’s LIDAR

facility, which is used for measurements of Earth’s ionosphere, open, as well as a 12-metre radio

telescope and the on-site visitors’ and science centres. “And we will be looking for ways to keep other

parts of the observatory operating,” says Gaume.

Arecibo was a giant 305-metre dish built into a natural depression, called a karst, in the mountains

and jungle of Puerto Rico. It was the largest single-dish telescope in the world until the building of

the Five-hundred-meter Aperture Spherical Telescope (FAST) in China in 2016. Its bowl-shaped

dish was covered in 38, 000 aluminium panels, which had been added to the telescope during an

upgrade in the early 1970s – prior to that the telescope, which was constructed in 1963, featured a

wire mesh as its reecting surface. e 1970s upgrade also saw the addition of a radio transmitter,

allowing the telescope to be used as a planetary radar, as well as for sending signals into deep space.

However, there are no current plans to rebuild Arecibo, or even to at least replicate its planetary

radar capability elsewhere. “e NSF has a well-dened multi-year process for building telescopes,

which includes getting congressional approval, so it’s too early to be able to comment,” says Gaume.

Timeline of discovery

The Arecibo radio telescope was the brainchild of William Gordon, a professor of engineering at Cornell University.
Devised in the 1950s, construction on it was completed by 1963. Originally it featured a wire mesh as its reflecting
surface; in 1974 the mesh was replaced by 38,000 aluminium panels giving greater resolution, and a planetary radar
transmitter was also added, used for probing the surfaces of the Moon, Venus and Mercury, and tracking and
characterising near-Earth asteroids. Although in later years it suffered from budget cuts, Arecibo kept doing science
right up until the collapse of the first cable in August.

• 1963 – sees first light


• 1967 – measures the rotation rate of Mercury as 59 days rather than 88 days, showing that the planet is not tidally-
  locked with a day of equal length to its year


• 1974 – discovers the first known binary pulsar, which has been subsequently used to test facets of the General
  Theory of Relativity


• 1974 – Arecibo’s director Frank Drake uses the newly installed radar transmitter to beam a brief radio message to
  any potential inhabitants of the globular cluster Messier 13, and the signal has gone down in SETI folklore as ‘the
  Arecibo message’


• 1989 – Arecibo makes the first radar image of an asteroid, 4769 Castalia


• 1992 – the planetary radar produces the first surface maps of Venus


• 1992 – astronomers using Arecibo discover the first known exoplanet around the pulsar PSR 1257+


• 1994 – Arecibo’s radar detects water-ice at Mercury’s poles


• 2016 – the first repeating fast-radio burst (FRB) is discovered in observations by Arecibo

An aerial view of Arecibo, showing the initial damage following the fall of two cables in August and November. The cables are

attached to three towers around the perimeter of the dish. The Gregorian dome can be seen hanging underneath the instrument

platform. Image: University of Central Florida.

The observing platform and Gregorian dish back in Arecibo’s better days. Image: University of Central Florida.

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Arecibo collapses after suffering ...

January 2021

Astronomy Now