The iconic Arecibo Observatory on the island of Puerto Rico is headed for demolition after a storied run scanning the cosmos.
A support cable snapped on the 305-meter radio telescope snapped in August. Engineering teams were making preparations to stabilize and repair the structure when a second cable broke on Nov. 6. On Thursday, the National Science Foundation announced its plans to decommission the observatory, citing the safety of workers, staff and visitors.
“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,” said NSF Director Sethuraman Panchanathan in a statement.
Over more than half a century, the sprawling radio telescope has helped conduct a massive, crowdsourced search for extra-terrestrial intelligence, solidified our understanding of exotic cosmic objects like neutron stars and even transmitted a message intended to announce humanity’s presence to anyone that might be able to pick up the signal beyond Earth.
Here’s a handful of the highlights from Arecibo’s long legacy of discovery.
Mercury’s swifter spin
In 1964, not long after it began operating, astronomers used Arecibo to determine that the planet Mercury does not spin quite as slowly on its axis as previously thought. Radar observations helped the scientists determine that the nearest world to the sun completes a single rotation in 59 days, a little faster than the previously assumed 88 days.
Mercury’s rotation rate was also found to be an orbital resonance with 2 orbits for every 3 rotations, rather than tidally locked.
Arecibo has been used to study Mercury many more times over its lifetime, and was instrumental in the revelation that the hot, rocky planet still manages to host ice at its poles.
A Nobel pulsar and more
Ten years later, a pair of scientists used Arecibo to find the first-ever binary pulsar. A pulsar is a pulsating neutron star, and a binary system is made up of two pulsars that orbit around a common center of mass.
Russell Alan Hulse and Joseph Hooton Taylor, Jr. used the massive dish to pick up radio emissions from the system cataloged as PSR B1913+16. Odd patterns in the pulses pointed to the presence of two pulsars rather than one. Data from the system also confirmed some of Albert Einstein’s predictions in his theory of general relativity.
While the discovery was made in 1974, Hulse and Taylor would go on to win the Nobel Prize in Physics for the find in 1993.
Arecibo was later used to find the first millisecond pulsar that was seen speeding up, a mysterious pair of pulsars that seem to disappear and later re-appear and also timed a pulsar in a triple system.
The first exoplanet
Today we’ve confirmed the existence of thousands of planets beyond our solar system and assume the galaxy to be filled with billions of worlds. But as recently as thirty years ago we had yet to confirm the presence of a single exoplanet.
The first extrasolar planets were discovered using Arecibo in 1992.
“They were three small planets named Draugr, Poltergeist, and Phobetor around the Lich Pulsar, a fast rotating neutron star that emits a beam of electromagnetic radiation,” Abel Mendez from the Planetary Habitability Laboratory of the University of Puerto Rico at Arecibo wrote in 2017.
The observatory has since been used to search not just for distant worlds, but also for distant signs of life.
Reaching out to E.T.
Arecibo never found any hard evidence of aliens, but it has been a critical tool over the decades in the search for extra-terrestrial intelligence and even to try and communicate with E.T.
In 1974, the radio receiver went into transmit mode to send the so-called “Arecibo Message,” which was a coded message directed at the M13 star cluster. The message contained some basic information about numbers, elements and DNA, along with some charmingly old-school images of a human, the solar system and the Arecibo observatory itself.
The Arecibo Message was meant more as a demonstration to celebrate a remodeling of the observatory rather than a serious scientific endeavor, but it did provide a firehose of data for the long-running effort [email protected]
The initiative used the processing power of numerous home computers running the program’s software to analyze radio signals for possible alien transmissions. At least at did, until it went on hiatus earlier this year.
Fast, Mysterious Bursts
One of the more recent enigmas in astronomy is the detection of fleeting radio emissions from deep space. Today, evidence points to pulsars as one possible explanation, so it should be no surprise that Arecibo has played a role in investigating the phenomenon during its more senior years.
Back in 2016, Arecibo was used to discover the first ever repeating fast radio burst. The find eliminated a number of potential causes involving catastrophic explosions and has allowed scientists to continue zeroing in on a source.