Arecibo telescope facts: Arecibo Observatory | Telescope, Collapse, Discoveries, & Facts

Arecibo Observatory: Watching for Asteroids, Waiting for E.T.

Arecibo Observatory, located in Puerto Rico, was the world’s second-largest single-dish radio telescope until its sudden collapse on Dec. 1, 2020. Despite strong support from the astronomy community to build a replacement facility, the National Science Foundation determined in 2022 it would not rebuild the iconic telescope. 

The striking Arecibo was iconic both for its science and for its appearance, as it included a platform suspended high above a gigantic radio dish, rising out of a tropical forest. 

Arecibo contributed an astounding catalog of astronomy work, including contributions that led to two Nobel prizes, during its half-century in operation. But it is perhaps most famous for being the site of the huge Search for Extraterrestrial Intelligence (SETI) message directed at the globular cluster M13 in 1974.

Besides its scientific work, Arecibo was the location of a climactic fight in «GoldenEye,» a 1995 James Bond film starring Pierce Brosnan. It also featured in «Contact,» a 1997 film based on a novel by Carl Sagan.

Related: The Arecibo Observatory: Puerto Rico’s giant radio telescope in photos

In February 2018, the National Science Foundation (NSF) — which provided most of the observatory’s funding since the 1970s — announced that it would cut its annual contribution from $8 million to $2 million in the following five years. In April 2018, the University of Central Florida in Orlando took over the management and operations of the observatory.  

Arecibo never made it that long. On Dec. 1, 2020, the radio telescope’s science platform collapsed after the National Science Foundation had decided the facility was too precarious to repair. Scientists around the world, but especially Puerto Rican astronomers, mourned its loss, but experts say the loss of the observatory was inevitable given the recent lack of funding for scientific infrastructure.

Read more: Possible cause of Arecibo Observatory telescope collapse 

From military observatory to civilian astronomy

The first function of Arecibo was supposed to be studying the ionosphere, a region of the upper atmosphere that is important to understand to properly transmit radio signals, according to an NSF fact sheet . The Advanced Research Projects Agency (today’s DARPA) was interested in this region to advance ballistic missile defense projects, which meant the observatory attracted military funding from the Office of Naval Research and the U.S. Air Force (as Space Force had not been created back then.)

The Air Force-managed telescope was dedicated in 1963 and hailed as the world’s largest radio telescope, but in a few short years it was already facing funding issues as ARPA’s research budget diminished. The NSF agreed to become Arecibo’s caretaker in 1967 and the research transferred to the civilian sector and astronomy.

NASA came on board in 1971 through a cost-sharing agreement with NSF, allowing for the dish reflector to be resurfaced and for more radar equipment to be added. The partners brought in a new dome and a second line for ionospheric radar in 1997. In these decades, NSF wrote, «Arecibo became a powerful tool for scientific research focused on ionospheric physics, radar and radio astronomy, and aeronomy. «

This image of asteroid 2015 TB145 was generated using radar data collected by the National Science Foundation’s Arecibo Observatory in Puerto Rico. (Image credit: NAIC-Arecibo/NSF)

When the telescope concluded its work, Arecibo was part of the National Astronomy and Ionosphere Center. The National Science Foundation had a cooperative agreement with the three entities that operated Arecibo: SRI International, the Universities Space Research Association and Puerto Rico’s Metropolitan University (UMET).

The reflective dish was 1,000 feet (305 meters) in diameter, 167 feet (51 m) deep, and covers an area of about 20 acres (81,000 square meters). A triangular platform was suspended 450 feet (137 m) above the dish by three concrete towers. The platform held the azimuth arm, a dome containing two subreflectors, and a set of antennae that could be tuned to a narrow band of frequencies.

Arecibo was the largest radio telescope until July 2016, when China finished the Five-hundred-meter Aperture Spherical Telescope’s (FAST) giant dish. That dish — the size of 30 football fields — is 1,650 feet (503 m) wide.

Key discoveries

A timeline of key discoveries made by the iconic Arecibo observatory.  (Image credit: Future)

Arecibo message

Arecibo broadcast a pictorial message into space in 1974, aiming for M13 — a globular cluster of stars. It will take some time for the message to get there, as M13 is about 21,000 light-years away.

According to SETI, the broadcast is roughly the same as a 20-trillion-watt omnidirectional broadcast. In simple terms, the broadcast would be visible by just about any receiver in the galaxy that is about the same size as the antenna at Arecibo.

These 14 radar images show the near-Earth asteroid Didymos (65803) and its moonlet as seen by the Arecibo Observatory radio telescope in Puerto Rico in November 2003.  (Image credit: NASA)

«We translated the radio-frequency message into a warbling audio tone that was broadcast over speakers at the ceremony. When [the tone] started, much of the audience spontaneously got up and walked out of the tent and gazed up at the telescope,» recalled past Arecibo director Harold Craft in a 1999 Cornell University press release marking the 25th anniversary.

In the decades following, SETI has trumpeted the message as a significant step to helping understand the challenges of communicating with aliens. «Although it’s unlikely that this short inquiry will ever prompt a reply, the experiment was useful in getting us to think a bit about the difficulties of communicating across space, time, and a presumably wide culture gap,» SETI wrote on its website .

Frank Drake, an astronomer famous for his work at Arecibo. (Image credit: wikipedia, CC BY-SA)

Tracking asteroids, exoplanets

Arecibo was frequently used for finding asteroids that swung close to Earth. The observatory focused on those that could pose a danger to the planet, making an effort to accurately measure their sizes and gauge the potential impact they could have. (To be sure, there are no immediate threats, but scientists keep searching just in case.)

In 2013, for example, the observatory watched the arrival of asteroid 2012 DA14, which passed within 17,200 miles (27,000 kilometers) of Earth. It was a close flyby, but NASA emphasized the asteroid passed by at a safe distance.

Besides asteroid research, Arecibo was also the site of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. The group has a habitable planets catalog that tracks the number of alien worlds in other solar systems that could be in the Goldilocks zone, or area that is not too hot or cold for life, of their respective stars.

Hurricane Maria moves across the Caribbean Sea as a Category 5 storm. (Image credit: NASA/NOAA GOES)

Hurricane Maria: Beginning of the end

On Sept. 20, 2017, Hurricane Maria ravaged the island of Puerto Rico, damaging the Arecibo Observatory. The Category 4 storm killed hundreds of people and caused widespread power outages that lasted for months. Power to the observatory was restored on Dec. 9, 2017.

The most significant damage was to the 96-foot (29 meters) «line feed» antenna, which was suspended above the radio dish. It broke off during the hurricane and punctured the dish below when it fell. A federal spending bill passed in February 2018 to provide relief to Puerto Rico allocated $16.3 million to repair the Arecibo Observatory.  

«Emergency repairs that needed immediate attention, such as patching roofs and repairing electrical feeds, have been underway since May after the site received hurricane-relief funding,» the University of Central Florida said in a statement issued in August 2018. «Additional repairs that will require more time and expertise will be completed as soon as possible.»

An image of the Arecibo Observatory’s iconic radio telescope as seen between two serious cable failures that preceded the facility’s collapse. (Image credit: University of Central Florida)

Decommission and collapse

On Aug. 10, 2020, one of the massive cables supporting the Arecibo Observatory radio telescope’s science platform failed, leaving a 100-foot gash in the radio dish below. Although at the time scientists were optimistic about potential repairs, on Nov. 6, 2020, another cable snapped, leaving the towers and platform too unstable to repair.

That was when, on Nov. 19, 2020, the NSF declared the observatory a loss. Researchers mourned the end of the iconic structure, especially Puerto Rican astronomers. One Puerto Rican scientist, Emily Alicea-Muñoz, said that it was a point of pride for the island. «We may be a tiny little island in the middle of the Caribbean,» she said, «but we can do big science.» 

Experts like Raquel Velho say the loss of the observatory was inevitable given the recent lack of funding for scientific infrastructure. A new inquiry was launched into the matter in February 2022 to determine what other factors, if any, created the sudden fall. While scientists remained hopeful that a new observatory would be constructed, the NSF announced in October 2022 that the funding was not available to make that happen, although they do plan to put an educational institution on the famed site.

«We were worried that it could be even worse than this, that they might say, ‘OK, just close down everything,'» Abel Méndez, an astronomer at the University of Puerto Rico at Arecibo who used the telescope in his research and teaching, told Space.com when the news was announced. «But my particular hopes were higher.»

This aerial view shows a hole in the dish panels of the Arecibo Observatory in Arecibo, Puerto Rico, on Nov. 19, 2020. (Image credit: RICARDO ARDUENGO/AFP via Getty Images)

Arecibo legacy

While Arecibo itself is no longer operational, its data always will be accessible through an archive and will allow scientists to make discoveries indefinitely. The telescope collected 57 years of data on pulsars, asteroids, galaxies, planets and many more interesting objects around the solar system and universe at large.

The impact of the Arecibo’s loss was felt around the globe. And not just by researchers, since the observatory became «potently symbolic, almost sacred» to those touched by the facility, according to science writer Nadia Drake . Drake’s family had been involved with Arecibo research for decades, particularly through her father Frank’s work with Project Ozma.

In a 2021 presentation at the 52nd Lunar and Planetary Science Conference (LPSC), presenters wrote that Arecibo left an «indelible mark on planetary science, radio astronomy, and space and atmospheric sciences,» and they expressed the sorrow surrounding its collapse in a wistful haiku: «Six decades’ service / Arecibo’s telescope / Lost, not forgotten.»

An image of Arecibo Observatory’s iconic radio telescope before damage that began in August 2020; the curved azimuth arm and the dome suspended from it are both visible. (Image credit: University of Central Florida)

Additional resources

 Watch an in-depth engineering video explaining why the Arecibo Telescope collapsed. Witness Arecibo’s decades of work with oral histories, written accounts and newspaper articles in this Cornell University guide .  

References

Arecibo Observatory. (n.d.) https://www.naic.edu/ao/landing  

Cornell Chronicle. (1999, Nov. 12.) «It’s the 25th anniversary of Earth’s first attempt to phone E.T.» https://news.cornell.edu/stories/1999/11/25th-anniversary-first-attempt-phone-et-0  

Drake, Nadia. (2021, Jan. 11.) «Why the loss of an iconic radio telescope is painfully personal.» National Geographic. https://www.nationalgeographic.com/science/article/why-the-loss-of-an-iconic-radio-telescope-is-painfully-personal  

Gonzalez Kotala, Zenaida. (2018, Aug. 14.) «Arecibo Observatory to Get $5.8 Million Upgrade to Expand View.» University of Central Florida. https://www.ucf.edu/news/arecibo-observatory-get-5-8-million-upgrade-expand-view/  

National Science Foundation. (n.d.) «Arecibo: Facts and Figures.» https://www.nsf.gov/news/special_reports/arecibo/Arecibo_Fact_Sheet_11_20.pdf  

National Science Foundation. (2022). «Arecibo Observatory: Media Resources. » https://www.nsf.gov/news/special_reports/arecibo/  

SETI Institute. (2022.) «Arecibo Message.» https://www.seti.org/seti-institute/project/details/arecibo-message  

SETI Institute. (2022.) «Project Ozma.» https://www.seti.org/project-ozma  

Taylor, P.A. and Rivera-Valentin, E.G. «The Legacy of Arecibo Observatory in Planetary Science and Beyond.» 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548). https://www.hou.usra.edu/meetings/lpsc2021/pdf/2179.pdf

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected]

Elizabeth Howell, Ph.D., is a staff writer in the spaceflight channel since 2022. She was contributing writer for Space.com for 10 years before that, since 2012. Elizabeth’s reporting includes an exclusive with Office of the Vice-President of the United States, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, «Why Am I Taller?», is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada’s Carleton University and (soon) a Bachelor of History from Athabasca University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.

With contributions from

  • Vicky SteinContributing Writer

Arecibo Observatory: Watching for Asteroids, Waiting for E.T.

Arecibo Observatory, located in Puerto Rico, was the world’s second-largest single-dish radio telescope until its sudden collapse on Dec. 1, 2020. Despite strong support from the astronomy community to build a replacement facility, the National Science Foundation determined in 2022 it would not rebuild the iconic telescope.  

The striking Arecibo was iconic both for its science and for its appearance, as it included a platform suspended high above a gigantic radio dish, rising out of a tropical forest. 

Arecibo contributed an astounding catalog of astronomy work, including contributions that led to two Nobel prizes, during its half-century in operation. But it is perhaps most famous for being the site of the huge Search for Extraterrestrial Intelligence (SETI) message directed at the globular cluster M13 in 1974.

Besides its scientific work, Arecibo was the location of a climactic fight in «GoldenEye,» a 1995 James Bond film starring Pierce Brosnan. It also featured in «Contact,» a 1997 film based on a novel by Carl Sagan.

Related: The Arecibo Observatory: Puerto Rico’s giant radio telescope in photos

In February 2018, the National Science Foundation (NSF) — which provided most of the observatory’s funding since the 1970s — announced that it would cut its annual contribution from $8 million to $2 million in the following five years. In April 2018, the University of Central Florida in Orlando took over the management and operations of the observatory.  

Arecibo never made it that long. On Dec. 1, 2020, the radio telescope’s science platform collapsed after the National Science Foundation had decided the facility was too precarious to repair. Scientists around the world, but especially Puerto Rican astronomers, mourned its loss, but experts say the loss of the observatory was inevitable given the recent lack of funding for scientific infrastructure.

Read more: Possible cause of Arecibo Observatory telescope collapse 

From military observatory to civilian astronomy

The first function of Arecibo was supposed to be studying the ionosphere, a region of the upper atmosphere that is important to understand to properly transmit radio signals, according to an NSF fact sheet . The Advanced Research Projects Agency (today’s DARPA) was interested in this region to advance ballistic missile defense projects, which meant the observatory attracted military funding from the Office of Naval Research and the U. S. Air Force (as Space Force had not been created back then.)

The Air Force-managed telescope was dedicated in 1963 and hailed as the world’s largest radio telescope, but in a few short years it was already facing funding issues as ARPA’s research budget diminished. The NSF agreed to become Arecibo’s caretaker in 1967 and the research transferred to the civilian sector and astronomy.

NASA came on board in 1971 through a cost-sharing agreement with NSF, allowing for the dish reflector to be resurfaced and for more radar equipment to be added. The partners brought in a new dome and a second line for ionospheric radar in 1997. In these decades, NSF wrote, «Arecibo became a powerful tool for scientific research focused on ionospheric physics, radar and radio astronomy, and aeronomy.»

This image of asteroid 2015 TB145 was generated using radar data collected by the National Science Foundation’s Arecibo Observatory in Puerto Rico. (Image credit: NAIC-Arecibo/NSF)

When the telescope concluded its work, Arecibo was part of the National Astronomy and Ionosphere Center. The National Science Foundation had a cooperative agreement with the three entities that operated Arecibo: SRI International, the Universities Space Research Association and Puerto Rico’s Metropolitan University (UMET).

The reflective dish was 1,000 feet (305 meters) in diameter, 167 feet (51 m) deep, and covers an area of about 20 acres (81,000 square meters). A triangular platform was suspended 450 feet (137 m) above the dish by three concrete towers. The platform held the azimuth arm, a dome containing two subreflectors, and a set of antennae that could be tuned to a narrow band of frequencies.

Arecibo was the largest radio telescope until July 2016, when China finished the Five-hundred-meter Aperture Spherical Telescope’s (FAST) giant dish. That dish — the size of 30 football fields — is 1,650 feet (503 m) wide.

Key discoveries

A timeline of key discoveries made by the iconic Arecibo observatory.  (Image credit: Future)

Arecibo message

Arecibo broadcast a pictorial message into space in 1974, aiming for M13 — a globular cluster of stars. It will take some time for the message to get there, as M13 is about 21,000 light-years away.

According to SETI, the broadcast is roughly the same as a 20-trillion-watt omnidirectional broadcast. In simple terms, the broadcast would be visible by just about any receiver in the galaxy that is about the same size as the antenna at Arecibo.

These 14 radar images show the near-Earth asteroid Didymos (65803) and its moonlet as seen by the Arecibo Observatory radio telescope in Puerto Rico in November 2003.  (Image credit: NASA)

«We translated the radio-frequency message into a warbling audio tone that was broadcast over speakers at the ceremony. When [the tone] started, much of the audience spontaneously got up and walked out of the tent and gazed up at the telescope,» recalled past Arecibo director Harold Craft in a 1999 Cornell University press release marking the 25th anniversary.

In the decades following, SETI has trumpeted the message as a significant step to helping understand the challenges of communicating with aliens. «Although it’s unlikely that this short inquiry will ever prompt a reply, the experiment was useful in getting us to think a bit about the difficulties of communicating across space, time, and a presumably wide culture gap,» SETI wrote on its website .

Frank Drake, an astronomer famous for his work at Arecibo. (Image credit: wikipedia, CC BY-SA)

Tracking asteroids, exoplanets

Arecibo was frequently used for finding asteroids that swung close to Earth. The observatory focused on those that could pose a danger to the planet, making an effort to accurately measure their sizes and gauge the potential impact they could have. (To be sure, there are no immediate threats, but scientists keep searching just in case.)

In 2013, for example, the observatory watched the arrival of asteroid 2012 DA14, which passed within 17,200 miles (27,000 kilometers) of Earth. It was a close flyby, but NASA emphasized the asteroid passed by at a safe distance.

Besides asteroid research, Arecibo was also the site of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. The group has a habitable planets catalog that tracks the number of alien worlds in other solar systems that could be in the Goldilocks zone, or area that is not too hot or cold for life, of their respective stars.

Hurricane Maria moves across the Caribbean Sea as a Category 5 storm. (Image credit: NASA/NOAA GOES)

Hurricane Maria: Beginning of the end

On Sept. 20, 2017, Hurricane Maria ravaged the island of Puerto Rico, damaging the Arecibo Observatory. The Category 4 storm killed hundreds of people and caused widespread power outages that lasted for months. Power to the observatory was restored on Dec. 9, 2017.

The most significant damage was to the 96-foot (29 meters) «line feed» antenna, which was suspended above the radio dish. It broke off during the hurricane and punctured the dish below when it fell. A federal spending bill passed in February 2018 to provide relief to Puerto Rico allocated $16.3 million to repair the Arecibo Observatory.  

«Emergency repairs that needed immediate attention, such as patching roofs and repairing electrical feeds, have been underway since May after the site received hurricane-relief funding,» the University of Central Florida said in a statement issued in August 2018. «Additional repairs that will require more time and expertise will be completed as soon as possible.»

An image of the Arecibo Observatory’s iconic radio telescope as seen between two serious cable failures that preceded the facility’s collapse. (Image credit: University of Central Florida)

Decommission and collapse

On Aug. 10, 2020, one of the massive cables supporting the Arecibo Observatory radio telescope’s science platform failed, leaving a 100-foot gash in the radio dish below. Although at the time scientists were optimistic about potential repairs, on Nov. 6, 2020, another cable snapped, leaving the towers and platform too unstable to repair.

That was when, on Nov. 19, 2020, the NSF declared the observatory a loss. Researchers mourned the end of the iconic structure, especially Puerto Rican astronomers. One Puerto Rican scientist, Emily Alicea-Muñoz, said that it was a point of pride for the island. «We may be a tiny little island in the middle of the Caribbean,» she said, «but we can do big science.» 

Experts like Raquel Velho say the loss of the observatory was inevitable given the recent lack of funding for scientific infrastructure. A new inquiry was launched into the matter in February 2022 to determine what other factors, if any, created the sudden fall. While scientists remained hopeful that a new observatory would be constructed, the NSF announced in October 2022 that the funding was not available to make that happen, although they do plan to put an educational institution on the famed site.

«We were worried that it could be even worse than this, that they might say, ‘OK, just close down everything,'» Abel Méndez, an astronomer at the University of Puerto Rico at Arecibo who used the telescope in his research and teaching, told Space. com when the news was announced. «But my particular hopes were higher.»

This aerial view shows a hole in the dish panels of the Arecibo Observatory in Arecibo, Puerto Rico, on Nov. 19, 2020. (Image credit: RICARDO ARDUENGO/AFP via Getty Images)

Arecibo legacy

While Arecibo itself is no longer operational, its data always will be accessible through an archive and will allow scientists to make discoveries indefinitely. The telescope collected 57 years of data on pulsars, asteroids, galaxies, planets and many more interesting objects around the solar system and universe at large.

The impact of the Arecibo’s loss was felt around the globe. And not just by researchers, since the observatory became «potently symbolic, almost sacred» to those touched by the facility, according to science writer Nadia Drake . Drake’s family had been involved with Arecibo research for decades, particularly through her father Frank’s work with Project Ozma.

In a 2021 presentation at the 52nd Lunar and Planetary Science Conference (LPSC), presenters wrote that Arecibo left an «indelible mark on planetary science, radio astronomy, and space and atmospheric sciences,» and they expressed the sorrow surrounding its collapse in a wistful haiku: «Six decades’ service / Arecibo’s telescope / Lost, not forgotten.»

An image of Arecibo Observatory’s iconic radio telescope before damage that began in August 2020; the curved azimuth arm and the dome suspended from it are both visible. (Image credit: University of Central Florida)

Additional resources

 Watch an in-depth engineering video explaining why the Arecibo Telescope collapsed. Witness Arecibo’s decades of work with oral histories, written accounts and newspaper articles in this Cornell University guide

References

Arecibo Observatory. (n.d.) https://www.naic.edu/ao/landing  

Cornell Chronicle. (1999, Nov. 12.) «It’s the 25th anniversary of Earth’s first attempt to phone E.T.» https://news.cornell.edu/stories/1999/11/25th-anniversary-first-attempt-phone-et-0  

Drake, Nadia. (2021, Jan. 11.) «Why the loss of an iconic radio telescope is painfully personal.» National Geographic. https://www.nationalgeographic.com/science/article/why-the-loss-of-an-iconic-radio-telescope-is-painfully-personal  

Gonzalez Kotala, Zenaida. (2018, Aug. 14.) «Arecibo Observatory to Get $5.8 Million Upgrade to Expand View.» University of Central Florida. https://www.ucf.edu/news/arecibo-observatory-get-5-8-million-upgrade-expand-view/  

National Science Foundation. (n.d.) «Arecibo: Facts and Figures.» https://www.nsf.gov/news/special_reports/arecibo/Arecibo_Fact_Sheet_11_20.pdf  

National Science Foundation. (2022). «Arecibo Observatory: Media Resources.» https://www.nsf.gov/news/special_reports/arecibo/  

SETI Institute. (2022.) «Arecibo Message. » https://www.seti.org/seti-institute/project/details/arecibo-message  

SETI Institute. (2022.) «Project Ozma.» https://www.seti.org/project-ozma  

Taylor, P.A. and Rivera-Valentin, E.G. «The Legacy of Arecibo Observatory in Planetary Science and Beyond.» 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548). https://www.hou.usra.edu/meetings/lpsc2021/pdf/2179.pdf

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected]

Elizabeth Howell, Ph.D., is a staff writer in the spaceflight channel since 2022. She was contributing writer for Space.com for 10 years before that, since 2012. Elizabeth’s reporting includes an exclusive with Office of the Vice-President of the United States, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, «Why Am I Taller?», is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada’s Carleton University and (soon) a Bachelor of History from Athabasca University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.

With contributions from

  • Vicky SteinContributing Writer

a magnificent error with a diameter of 305 meters

Leonid Hurwitz,
professor of the Joint European Institute of Radio Interferometrics and Delft University of Technology (Netherlands)
«Trinity variant — Science» No. 25(319), December 22, 2020

Edition. In December of this year, a sad event happened in astrophysics: a final decision was made to close the Arecibo radio telescope with more than half a century of glorious history. The telescope was finished off by the elements — first an earthquake, then a typhoon. On December 1, the cables burst, and a heavy platform with a receiver and transmitter fell onto a huge antenna. Tool repair would be too complicated and dangerous.

In this issue we present a selection of materials dedicated to the Arecibo: an article by Leonid Gurvits about the history of the instrument, an essay by Boris Stern (p. 5) about the most striking discoveries made with the radio telescope, Vladimir Soglasnov’s reminiscences of a New Year’s business trip to Puerto Rico ( p. 6) and a note by Yuri Kovalev on the joint work of Radioastron and Arecibo (p. 9).

Late 1950s. The Soviet Union marches triumphantly from one space victory to another: the first satellite, the first flight around the moon, the first manned flight into space is not far off. Of course, all this was the embodiment of the dream of flying to the stars. But there were other motives for the development of Soviet rocket and space technology. Newspapers did not write about them.

The entire Soviet breakthrough into space was based on the «Magnificent Seven» — the R-7 rocket, built under the leadership of Sergei Pavlovich Korolev, who was tasked with creating a means of delivering a hydrogen bomb to another continent. Korolev and his colleagues coped with this task brilliantly. This could not but disturb those to whom the rocket cargo was intended. Countermeasures were urgently needed, in particular, the ability to instantly register the launch of strategic missiles from launch sites far beyond the horizon, on the other side of the planet.

The designers of the so-called over-the-horizon radars placed great hopes on the «opacity» of the earth’s ionosphere at meter and longer radio waves. The lower edge of the ionosphere on one side and the Earth’s surface on the other created a kind of waveguide in which direct and reflected radar signals propagated. But their propagation was complicated, many parameters of such a waveguide were unclear. Taking off intercontinental missiles and their warheads moving towards the target pierced the ionosphere and upper atmosphere, leaving various traces there. They also had to learn to recognize them. In short, the study of the ionosphere became a task of strategic importance.

Around the same time, radiophysicist William Gordon of Cornell University proposed an experimental setup to study the density and temperature of the ionosphere from the so-called incoherent «backscattering» of radio waves by free electrons. The heart of the installation was to be a powerful radar, radar. Gordon estimated the power of the direct and reflected signals using the data available at that time on the distribution of electron density and «substituting» these quantities into the well-known formulas for the Thomson scattering of electromagnetic radiation. The reflected signal was rather weak. According to Gordon, recording the desired effect required a receiving antenna no less than 300 m in diameter. Interest in ionospheric topics was also fueled by the fact that it was in the center of attention of the program of the International Geophysical Year (1957–1958).

But besides ionospheric tasks, Gordon and his colleagues thought about other possible applications of a large radar — for example, planetary and solar research. These tasks required placing the radar not too far from the equator. By the fall of 1958, it was clear that among many potential telescope locations, the tropical island of Puerto Rico was in the lead: a latitude of about 18 degrees north, many natural karst sinkholes that would help to significantly reduce the cost of soil sampling. But the main thing is the territory under American control: the American military firmly insisted on this, showing increasing interest in the project. They also helped to obtain the necessary funding for the construction of a giant facility. As a reflector, a spherical bowl was chosen, formed by a metal mesh and looking at the zenith. And it was decided to place the antenna feed on a platform suspended on powerful steel cables supported by three high concrete towers.

The construction of the antenna began in the vicinity of the provincial (even by Puerto Rican terms) town of Arecibo about a year after the first design estimates. But even before its completion, several Cornell astrophysicists and William Gordon himself began to realize that an error crept into the calculations of the necessary sensitivity of the receiving antenna: the Doppler broadening of the spectral line of the scattered signal is about a hundred times less than it was originally supposed. Accordingly, the signal intensity in this line should be two orders of magnitude higher than the calculated one. Translated into a language understandable to the financiers of the project: in the initial calculations, the required antenna area was overestimated a hundred times, therefore, its diameter could be made ten times smaller, and the cost was even scary to think. .. According to unconfirmed legend, this understanding served cause several serious heart attacks. But a mistake is a mistake, and it was no longer possible to stop the project, the antenna had to be built.

The very first ionospheric experiments with a 305-meter antenna at a frequency of 430 MHz (wavelength about 70 cm) answered all the initial radiophysical questions with a huge margin of sensitivity. The question arose: what to do next?

And then scientific work began, inaccessible to any other instrument. Indeed, the area of ​​​​the collecting surface of the Arecibo antenna exceeded the total area of ​​\u200b\u200ball other radio telescopes that existed at that time, combined. (Let’s not forget that the sensitivity of a telescope is directly proportional to the area of ​​its surface collecting radio emission.) At the same time, the Arecibo antenna complex, unlike the vast majority of other radio astronomy instruments, could operate both in passive (reception only) and active (radiation) modes.

After the official «inauguration» of the Arecibo observatory, which took place on November 1, 1963, work was launched in three scientific areas: the study of the ionosphere and the upper atmosphere of the Earth; radar research of the solar system; galactic and extragalactic radio astronomy. In the next half century, the share of these three areas in the work of the observatory varied slightly, but they all remained on the agenda.

Just a list of all the outstanding achievements of the unique Arecibo radio telescope would take up the lion’s share of a newspaper spread. Let’s name just a few of them.

Detailing the physical processes of incoherent scattering in the Earth’s ionosphere with the help of active and passive Arecibo instruments has significantly exceeded the requirements set by the original task. In the era of direct satellite experiments in the ionosphere and magnetosphere of the Earth, the Arecibo instruments became the most reliable combination of direct and remote measurements of the plasma component of the near-Earth space.

The very first experiments on the radar of Mercury led to the discovery of an unexpected spin-orbital resonance: two Mercury years are strictly equal to three Mercury days. Such an elegant arithmetic phenomenon says a lot about the process of formation of our planetary system. The radar of Titan, a satellite of Saturn, indicated the existence of dried hydrocarbonate lakes — the so-called paleolakes. Where there are lakes, there is liquid; where there is liquid, there can be life… In addition, the Arecibo radar significantly supplemented our understanding of the topography of the surface of Venus. Relatively recently, the task of searching for asteroids dangerous for the Earth was added to the program of the Arecibo observatory.

The Arecibo radio telescope has for several decades been the most sensitive instrument for studying pulsars — rotating neutron stars with a magnetic field. It was thanks to Arecibo that the first millisecond pulsar and the first exoplanet orbiting a neutron star were discovered. Careful monitoring of the evolution of the period of a pulsar in a binary star system allowed Joseph Taylor and Russell Hulse to experimentally confirm the existence of gravitational waves for the first time — the authors of the discovery were awarded the Nobel Prize in Physics 1993 years old

Long-term observations at Arecibo helped to build the most detailed three-dimensional maps of the distribution of atomic hydrogen in the vicinity of the Galaxy. The development of technology, which allowed the 305-meter telescope to register mysterious ultrashort cosmic radio bursts, and the LIGO and VIRGO installations — gravitational waves, led to the emergence of a new branch of science — multi-information astronomy ( multi-messenger astronomy ; there is also a translation of ‘multi-channel astronomy’. — Rev. ).

Beginning in the 1960s, Arecibo played an important role in the search for extraterrestrial civilizations and even attempts to address these hypothetical civilizations through special radio messages.

All of the above cannot be recognized as a mistake by William Gordon and his colleagues. More such «mistakes»! Not without reason, in 2010, the 305-meter radio telescope was given the official name of the William Gordon Radio Telescope.

For the first ten years of its existence, the Arecibo Observatory was operated by Cornell University on behalf of and with financial support from the Advanced Research Projects Agency (ARPA). It was formed by President Eisenhower to coordinate the American response to the Soviet satellite launch. Early 19In the 1970s, the Arecibo observatory came under the umbrella of the US National Science Foundation, but continued to be managed by Cornell University until 2013.

In the early 1970s, the Arecibo radio telescope was radically upgraded. The grid reflective surface of the main mirror has been replaced with a solid one formed from aluminum panels; this made it possible to expand the frequency range, bringing its upper limit to 3 GHz (wavelength — 10 cm). A new transmitter for planetary radar was installed at a frequency of 2.3 GHz with a record power of 420 kW for its time. Twenty years later, a second major overhaul was carried out, which included the installation of a screen around the perimeter of the main mirror to reduce unwanted noise, as well as a new large secondary reflector, which allowed the upper operating frequency to be raised once again — this time to 10 GHz. The transmitter power was increased to 2 MW. In the last ten years, an instrumental foundation has been laid for advanced research on the search for gravitational waves in the nanohertz range, «radio photography» of the sky in the spectral line of atomic hydrogen at a wavelength of 21 cm, radio interferometric experiments as part of the European and global networks, and much more.

In addition, the work of the Arecibo radio telescope has become a prerequisite for the development of general and academic education on a tropical island. «El Radar» (as the local Spanish-speaking population of the island calls the antenna) has become a symbol of Puerto Rico to no less extent than the musical «West Side Story». For several decades, almost all schoolchildren in Puerto Rico have visited the Arecibo Observatory, its museum and excellent educational center at least once. Thousands of young Puerto Ricans have chosen their professional path under the influence of the scientific and technological miracle «El Radar».

However, at the beginning of our century, a difficult period began for the observatory. The US National Science Foundation has decided to cut its share of funding for Arecibo by a factor of four, inviting other interested agencies or sponsors to take on the burden of the costs. The reason was the huge budget burden associated with the maintenance of new priority and very expensive astronomical observatories, such as the Atacama Millimeter Aperture Synthesis System (ALMA, Atacama Large Millimeter Array ) and Vera Rubin Optical Observatory. Partial funding for Arecibo was continued by NASA and other government departments and private universities. A massive attack on the island by natural forces also coincided with the period of organizational upheaval: powerful tropical hurricanes and more frequent earthquakes badly battered the infrastructure of the observatory. The University of Central Florida, which took over the observatory in 2017, struggled to manage the complex and still very scientifically and educationally productive Arecibo instrumentation.

The current coronavirus year has dealt an almost knockout blow to the observatory ( the author asks not to consider this statement as a reference to the intrigues of higher powers and other devilry ). In August 2020, one of the auxiliary cables providing mechanical stabilization of the 900-ton focal platform collapsed and damaged the reflecting surface of the telescope during a fall. Considerable funds (several million dollars) were urgently sought for repairs. The renovation was about to begin. But on December 1, 2020, 57 years and one month after the «inauguration» of the observatory, there was a catastrophic rupture of one of the three groups of power cables that supported the platform. She collapsed from a height of 150 meters onto the bowl of the main reflector. It is impossible to repair the unique equipment that was on the platform. The reflective surface also suffered significant damage. Two weeks before this disaster, based on the conclusions of several independent experts, the US National Science Foundation announced its decision to dismantle the 305-meter radio telescope.

Does this mean the complete and final end of radio astronomy and radar research in Puerto Rico? This question is at the center of the almost non-stop and sometimes very emotional debate in the world scientific community in recent weeks. There is a point of view that the Arecibo radio telescope has played its role and should become history. Today there are new instruments: for example, the Chinese FAST radio telescope ( Five-hundred-meter Aperture Spherical Telescope ). But it does not have the capabilities of the Arecibo radar, and its instrumentation is different. The Chinese telescope will not be able to replace Arecibo in radio interferometric studies either. In addition to the negative scientific and practical effect, it is difficult to overestimate the moral damage from the loss of El Radar, beloved by Puerto Ricans.

Several initiative groups at once are trying to organize a broad campaign in support of the creation of a new, commensurate scientific instrument in the place of the fallen titan. An example of such a revival exists: in 19On the 88th, the 100-meter radio telescope of the Green Bank National Radio Astronomy Observatory in West Virginia collapsed. State Senator Robert Byrd was able to quickly mobilize government support for the construction of a new, slightly larger and much more advanced telescope at the same observatory. Today, this Senator Byrd-named instrument is the largest full-rotation radio telescope on the planet. Optimists hope that with the advent of the Biden administration (which promises to treat science more respectfully than its predecessor), the fate of the Arecibo-2.0 radio telescope is not hopeless.

The Arecibo radio telescope has died. Long live the Arecibo radio telescope!

A Russian astronomer commented on the demolition of the Arecibo telescope

Why it was decided to demolish the famous Arecibo telescope, what discoveries it became famous for and how local frogs interfered with astronomers, Yuriy, corresponding member of the Russian Academy of Sciences, head of the scientific program of the Russian Radioastron project, told Gazeta.Ru Kovalev.

One of the world’s largest radio telescopes, the famous Arecibo Observatory in Puerto Rico, is living its last days. The day before, a decision was announced in the United States, which astronomers around the world are discussing and bitterly conveying to each other — due to a series of breakdowns and security problems, one of the greatest astronomical instruments in human history will be demolished.

The problems with the telescope began in August of this year, when it was put out of action due to a broken cable.

As a result of a break in the cable supporting the feed of the antenna, a hole 30 meters in size formed in the main mirror of the telescope with a diameter of 300 meters — frames with this break flew around the world.

Yesterday, the US National Science Foundation announced its decision to shut down the telescope after repeated safety reviews of its structures.

Management has concluded that the tool is “in danger of catastrophic collapse and its cables can no longer support the design load”.

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View of the Arecibo radio telescope, November 2020 View of the Arecibo radio telescope, 2003 Arecibo radio telescope Tourists at the Arecibo radio telescope, 2006 Arecibo radio telescope

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In addition, the calculations showed that any attempt to repair would endanger the lives of specialists. The engineers hired for the evaluation decided to use controlled demolition of the telescope structures to avoid repeated cable breaks.

Yury Kovalev, corresponding member of the Russian Academy of Sciences, head of the scientific program of the Russian Radioastron project, shared his personal memories of the legendary telescope and thoughts about its demolition with Gazeta. Ru.

“It so happened that some of my colleagues still have an application for observations on Arecibo, which they did not have time to observe. What can you do, that’s life. And so it was with Radioastron.

This story has two sides. One is purely human and emotional. Astronomers are living people, and when they work on certain telescopes, they do not treat them like a pile of iron, but associate a considerable number of feelings with them, and usually these feelings are positive. Entire periods of human lives are associated with them, many of them began their careers on one telescope or another. And it is clear that Arecibo is not just some kind of telescope.

This telescope does not see the whole sky, but some one area, since the main mirror is stationary. The shape of the surface is a sphere. It never works as a whole — these 300 meters do not simultaneously collect the signal of a space object. The secondary mirror has a very tricky shape, it moves along the cables. This allows you to use different parts of this 305-meter spherical mirror at different times.

And I was once told: you see, in that part of the sky that «Arecibo» sees, there is nothing for other telescopes to do. It’s a matter of sensitivity. «Arecibo» so outshines all the others in terms of sensitivity that other instruments really have nothing to catch there. This capacious description I remembered for the rest of my life.

The construction of the telescope began in 1960, its original purpose was to study the Earth’s ionosphere. He began work in 1963, with the help of Arecibo, many discoveries were made, including the discovery of a number of pulsars and new data on Mercury.

On November 16, 1974, the famous “Message Arecibo” was sent using a telescope, a radio signal directed to the globular star cluster M13, located at a distance of 25 thousand light years in the constellation Hercules.

The message contained information about man and mankind, molecular formulas of DNA nucleotide components, numbers from 1 to 10 in the binary system, and other data.

The reflector of the telescope is located in a natural sinkhole and is covered with almost 40,000 perforated aluminum plates measuring 1×2 m, laid on a grid of steel cables. Pointing the telescope to a given point in the sky is carried out by moving the movable antenna feed, suspended on 18 cables from three towers.

“When people look at his pictures and think it’s a solid 305-meter mirror, it’s not. I thought so myself until I came to the observatory to give a lecture. This mirror is a very fine mesh, which is suspended by braces, and now you can see it better when they show a photo of a break in the surface. As a result, the «Arecibo grid» operates in the range from meters to about 4 centimeters, says Kovalev. —

We can confidently say that the ground-space base of the Arecibo system — Radioastron — was the most sensitive of all that we had in the project.

Therefore, indeed, many scientists are grateful to this telescope for the unique results that have defined the careers of many. The other side of the coin — is it the right decision to close? I believe that the decision is absolutely correct. To be honest, it was so obvious and expected that I was just waiting — when?

The observatory believes that the breakage of the second cable is due to the fact that after the loss of the first cable, the load on the remaining cables became higher, Kovalev notes.

“And since several months had passed since the break of the first cable, and they could not do anything quickly, and the second cable broke, sorry, the telescope was doomed. Any boss had no right not to make a decision dictated by security issues, because if something happens, you will be to blame, ”he believes.

The scientist said that about 10 years ago, NSF conducted a very painful analysis on the question of which ground-based American telescopes to reduce in order to have enough money for the ALMA observatory (Chile).

“Surprisingly, NSF budgeted for the construction of ALMA, but did not pre-budget for its operation, which is very expensive. The commission recommended closing some of the optical telescopes and switching to partial financing of the Green Bank, VLBA and Arecibo radio telescopes. The other half for their budgets is to look on the side. As a result, the Arecibo observatory has been in a financially difficult situation in recent years.

This is a typical approach of officials and scientific foundations, and it is quite correct — to build new telescopes, solve new scientific problems, and close the old ones.

Russian officials told us the same thing. But the devil is in the details. It is right to first build new modern world-class telescopes and put them into full-fledged operation. And only then close the obsolete ones. And the Americans do just that, otherwise you can be left with a bare ass. And the same Arecibo was not closed, it worked until the last moment, ”said Kovalev.

The astrophysicist shared his personal impressions of visiting the famous telescope.

My main telescope memory is frogs.

The small tree frogs living there croak all the time,” recalls Kovalev. “Local astronomers said that when they had teleconferences, foreign colleagues complained about the noise and asked to turn it off. “We can’t turn them off – there are thousands of them around,” they answered. Under this net, stretched on cables, you can safely go for a walk, trees and various plants grow under it. The puddle is small. It is interesting that under the net «Arecibo» there is always partial shade due to holes. And thanks to this, there is a special microclimate, plants that are specific to it grow.

And another memory — fear.

There is a narrow path leading to a huge cabin hanging over a hundred meters above the surface of the telescope. You walk along it, holding on to the cable, like agent 007 from the famous movie. And you only have one life.»

According to the astronomer, the demolition of the telescope will not be a big loss for world astronomy.

“Over time, the SKA project (short for Square Kilometre Array) will definitely replace Arecibo,” he believes.

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