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A legendary radio telescope passes into history

A legendary radio telescope passes into history

The giant radio telescope Arecibo will soon cease to exist, as decided by the US National Science Foundation (NSF). The enormous antenna has been breaking down for quite a long time, and, according to experts, its possible repair would be too dangerous to its future operators. Dr Elżbieta Kuligowska from the Astronomical Observatory of the Jagiellonian University gives a commentary on the decommissioning of one of the world’s most famous astronomical facilities.

The giant radio telescope Arecibo will soon cease to exist, as decided by the US National Science Foundation (NSF). The enormous antenna has been breaking down for quite a long time, and, according to experts, its possible repair would be too dangerous to its future operators. Dr Elżbieta Kuligowska from the Astronomical Observatory of the Jagiellonian University gives a commentary on the decommissioning of one of the world’s most famous astronomical facilities. 

With 305 metres in diameter, Arecibo still remains one of the world’s largest single-aperture radio telescopes. Located near the town of Arecibo in Puerto Rico, it has been used for research in radio astronomy, atmospheric science, and radar astronomy by the Cornell University, SRI International, Universities Space Research Association, and the Metropolitan University of Puerto-Rico, in collaboration with the NSF. The access to the telescope has also been granted to other research institutions. From 1963, when it was built, until 2016 it was the largest single-aperture radio telescope in the world. In 2016 it was surpassed by the larger FAST radio telescope in China (500 metres in diameter).

The Arecibo radio-telescope is a unique, iconic device, considered one of the best-recognised symbols of science in the world. It was used for a number of purposes, including studying the rotation of Mercury, research into stars, pulsars, asteroids, nebulae and galaxies, discoveries of first exoplanets (extrasolar planets), as well as sending the first intentionally created radio signal addressed to hypothetical extra-terrestrial civilizations into outer space.

The graphical representation of the Arecibo message – the mankind’s first attempt to communicate with extra-terrestrial beings

In 1990 the Polish astronomer Aleksander Wolszczan used observations with the Arecibo telescope  to discover the pulsar PSR B1257+12, which later led to his discovery of its three orbiting planets – the first known exoplanets.

Besides “standard astronomy”, the telescope was also used by the US intelligence to determine the location of Soviet radar stations, based on their signals bounced off the moon, whereas in 1974 it sent the message addressed to potential “aliens” towards the Hercules Globular Cluster. For a long time, the radio telescope also served as the main source of data in the SETI@home project of the search for extra-terrestrial civilizations (currently coming to an end, at least in its current form). In 2008 the Arecibo Observatory was inscribed on the National Register of Historic Places.

The iconic radio telescope also became part of the popular culture. It was featured in the 1995 GoldenEye movie from the James Bond series as well as Nintendo 64 game GoldenEye 007. It could also be seen in Contact – a film based on Carl Sagan’s novels and in one of X-Files episodes (Little green men). Arecibo observatory has been shown in a number of documentaries, including and the 12th episode of Cosmos: A Personal Voyage, entitled Encyclopaedia Galactica.

On 10 August 2020, the radio telescope suffered a serious technical failure: one of the wires upholding the metal platform above the device broke and smashed into the dish, tearing a 30-metre gash in it and damaging several panels in the so-called Gregorian Dome above it. Several days ago, experts assessed the possible repair of the facility as too risky.

After an inspection showed that the damage cannot be repaired without risking the life of the construction workers and the staff of the facility in the future, the NSF started planning to decommission the radio telescope after 57 years of service as an important source of invaluable astronomical data. The decision was made after a careful analysis of numerous assessments by independent engineering teams, which unanimously concluded that the telescope would be in danger of a disastrous breakdown, as its cables could no longer be capable of bearing the load they were initially designed to sustain. Besides, in several assessments it was pointed out that even if the repairs are successful, the entire structure will suffer from stability problems.  

NSF prioritizes the safety of workers, Arecibo Observatory’s staff and visitors, which makes this decision necessary, although unfortunate," said the NSF Director Sethuraman Panchanathan. "For nearly six decades, the Arecibo Observatory has served as a beacon for breakthrough science and what a partnership with a community can look like. While this is a profound change, we will be looking for ways to assist the scientific community and maintain that strong relationship with the people of Puerto Rico."

GoldenEye movie still with Arecibo dish in the background

After 10 August 2020, the engineering teams designed and were ready to implement an emergency structural stabilisation of the auxiliary cable system. But when the delivery of replacement auxiliary cables and temporary cables was already arranged, the main cable on the same tower broke on November 6. Based on the stresses on the second broken cable, which should have been able to function well, the engineers concluded that the remaining cables can also be weaker than originally assumed.

The scope of the NSF's decommissioning plan focuses not only on the 305-metre telescope. It also aims to ensure the safety of other parts of the observatory that could be damaged or destroyed in the event of an unplanned collapse of the entire dish. The plan envisages preserving as much of the remaining infrastructure of Arecibo Observatory as possible, so that it remains available to research and educational missions in the future.

The decommissioning process includes devising a technical execution plan and ensuring compliance with a number of legal, environmental, safety and cultural requirements. After the telescope decommissioning, the NSF is going to restore the operation of some facilities, such as the Arecibo Observatory LIDAR, very useful for geospace research as well as the visitor centre and the Culebra facility (located further away from the main site), where the weather data, including cloud cover and precipitation, are analysed. Part of the research conducted in Arecibo, such as the analysis and cataloguing of archived data collected by the radio telescope, will also continue.

"Leadership at Arecibo Observatory and UCF did a commendable job addressing this situation, acting quickly and pursuing every possible option to save this incredible instrument," concluded Ralph Gaume, Director of the NSF's Division of Astronomical Sciences. "Until these assessments came in, our question was not if the observatory should be repaired but how. But in the end, a preponderance of data showed that we simply could not do this safely. And that is a line we cannot cross."

Original text by Dr Elżbieta Kuligowska from the JU Astronomical Observatory: www.nauka.uj.edu.pl

 

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