By: Byron Perry
The Arecibo Observatory
The 300m wide dish, nestled in the Puerto Rican jungle. You can clearly see the damage caused by the broken cable. (National Science Foundation)
The Arecibo Observatory is probably the most famous Earthbound telescope, serving humanity's quest for knowledge for 57 years. The iconic structure has featured in the James Bond movie Goldeneye and is responsible for many massively important scientific discoveries. Unfortunately, it has recently had two support cable failures in August and November 2020 (National Science Foundation), and it is too dangerous to repair and thus will be demolished.
The Arecibo Observatory consists of a radio dish 305 meters (1000 feet) in diameter. The dish reflects radio waves coming in from outer space up to a 914 metric tonne (900 imperial ton) instrument array hanging above the dish. The array is supported by cables coming from three towers surrounding the dish (National Science Foundation). From 1963-2016 it was the largest radio telescope in the world, until it was surpassed by the FAST telescope in China (SETI). The observatory is so large it had to be built in a natural sinkhole, deep in the picturesque jungles of Puerto Rico. On August the 10th 2020, a secondary, smaller cable snapped leaving a 30 meter (100 foot) long gash in the dish. Then, on the 6th of November a main cable snapped. These successive failures put the telescope in jeopardy, and on the 19th November 2020 engineers working for the University of Central Florida, and the National Science Foundation concluded it would be too dangerous to repair and decided to decommission the Observatory (National Science Foundation). This is a massive loss for science as some of the capabilities of the Observatory are possessed by no other telescope, and the loss of what is a science icon has saddened many. Criticisms have been made that maintenance was not funded adequately, and that the problem should have been spotted sooner (Nature).
History of the Arecibo observatory
Construction on the Arecibo Telescope started in 1960 and it was envisaged as a tool for both the national defense of the USA, and for science. In 1960 the Cold War was at its height and the Department of Defense would fund any project that could give the USA an edge over the USSR. At the time, the Department of Defense was trying to develop Anti Ballistic Missile systems (ABM’s). It was predicted that ballistic missile warheads (containing nuclear bombs) reentering from space into the Earth's ionosphere would ionise gas particles, and this would be detectable using a radio telescope as ionised particles reflect radio waves (Pennsylvania State University). Ionisation is when gas particles lose their electrons to become imbalanced in electric charge, and the ionosphere is the layer of the atmosphere in which radiation from the sun ionises gas atoms. Fortunately for astronomy, the physicists at Cornell University overestimated the size of the radio dish needed to detect missiles, and calculated a 305 metre (1000 foot) dish would be needed (Pennsylvania State University). In actuality, a much smaller dish can be used. It was constructed from 1960-1963 and until 2020 was used in the fields of astronomy, planetary science and even planetary defense.
The Arecibo Observatory, due to its original role in detecting missiles can not only receive radio waves but also actively use radar (radio waves used to image an object) to image astronomical bodies. The observatory was used to conduct a large amount of research into pulsars. Pulsars are either white dwarfs or neutron stars. White dwarfs are the burnt out remnants of long dead stars, small and very hot. Neutron stars are the collapsed cores of stars far larger than our sun. They are massively dense and small. A neutron star that is 20 km (12.4 miles) in diameter masses more than the sun! What makes these bodies pulsars is that they spin very rapidly emitting beams of radiation. Somewhat like a space lighthouse.
Some of the discoveries made by the Arecibo observatory include:
In 1974 astrophysicists Russel Alan Hulse and Joseph Hooton Taylor won the Nobel Physics Prize for their discovery of the first binary pulsar (2 pulsars in the same system).
The discovery of the first exoplanet (planet in a different solar system to our own), which was orbiting a pulsar (Frail and Wolszczan 1992).
Using radar to map ice on the poles of Mercury (Harmon 1994).
However what Arecibo Observatory is most famous for is the Arecibo message. This was a radio message sent in 1974 directed at the M13 star cluster 25000 light years away. It tells a potential alien species about humans, including what we look like and information concerning our DNA. It will arrive in the year 26,974! (SETI Institute).
A graphical depiction of the Arecibo message, which is in binary, (SETI Institute).
To conclude the Arecibo Observatory was a cultural and scientific icon. It changed our perception of the universe forever, and added considerably to the bank of human knowledge.
11 days after I first wrote this article the nail in the coffin came for the Arecibo observatory when on the 1st December 2020 the 900 ton instrument array came crashing down after the rest of the cables holding the array suspended failed (National Science Foundation). This is a heartbreaking development and shatters any hopes of the telescope being rescued. Fortunately no one was injured by the collapse but the picture below shows the scale of the collapse and the destruction caused.
The collapsed and twisted instrument array on the left and shattered dish. (Nature)
Frail, D. A., and A. Wolszczan. “A planetary system around the millisecond pulsar PSR1257 + 12.” Nature, vol. 355, no. 6356, 1992, pp. 145-147. https://ui.adsabs.harvard.edu/, https://ui.adsabs.harvard.edu/abs/1992Natur.355..145W/abstract. Accessed 20 November 2020.
Harmon, J. K. “Radar mapping of Mercury's polar anomalies.” Nature, vol. 369, no. 6477, 1994, pp. 213-215. https://ui.adsabs.harvard.edu/, https://ui.adsabs.harvard.edu/abs/1994Natur.369..213H/abstract. Accessed 20 November 2020.
Hulse, R. A., and J. H. Taylor. “Discovery of a Pulsar in a Binary System.” Astrophysical Journal, vol. 195, 1975, pp. 51-53. https://ui.adsabs.harvard.edu/, https://ui.adsabs.harvard.edu/abs/1975ApJ...195L..51H/abstract. Accessed 20 November 2020.
National Science Foundation. “NSF begins planning for decommissioning of Arecibo Observatory’s 305-meter telescope due to safety concerns.” nsf.gov, nsf.gov, 19 November 2020, https://www.nsf.gov/news/news_summ.jsp?cntn_id=301674. Accessed 20 November 2020.
Nature. “Legendary Arecibo telescope will close forever — scientists are reeling.” nature.com, nature.com, 19 November 2020, https://www.nature.com/articles/d41586-020-03270-9. Accessed 20 November 2020.
Nature. “Gut-wrenching photos document Arecibo telescope's collapse.” nature.com, nature.com, 2 December 2020, https://www.nature.com/articles/d41586-020-03421-y. Accessed 3 December 2020.
Pennsylvania State University. “A short history of geophysical radar at Arecibo Observatory.” https://hgss.copernicus.org, Pennsylvania State University, 13 March 2013, https://hgss.copernicus.org/articles/4/19/2013/hgss-4-19-2013.pdf. Accessed 20 November 2020.
SETI. “World Biggest Radio Ear.” seti.org, seti.org, 5 October 2016, https://www.seti.org/seti-institute/worlds-biggest-radio-ear. Accessed 20 November 2020.
SETI Institute. “Arecibo Message.” seti.org, seti.org, https://www.seti.org/seti-institute/project/details/arecibo-message. Accessed 20 November 2020.