It’s the end of an era for one of astronomy’s most famous telescopes. After a series of accidents at the Arecibo Observatory in Puerto Rico, its giant telescope, once the largest radio telescope in the world, is being decommissioned.
Its closure marks not just the end of the story for this landmark, but perhaps the beginning of the end for giant telescopes as the cutting edge of astronomical instruments.
Arecibo’s troubles began in August this year, when an auxiliary cable stretched over the 1,000-foot reflector dish snapped and fell, ripping a 100-foot-long gash in its surface. The facility was already in a precarious position following damage from Hurricane Maria in 2017, and the snapping cable forced the halting of its operations.
Fortunately, no one was hurt in the accident. However, the National Science Foundation (NSF), which oversees the observatory, said the structure was “in danger of a catastrophic failure.” Still, engineers remained hopeful that the cables and the dish could be repaired.
But in early November, the observatory suffered another serious incident when a main cable failed, likely due to the extra load it was carrying without the auxiliary cable to support it. Within the month, the NSF announced it could not safely repair the damage and would decommission the telescope.
Built between 1960 and 1963, the telescope was renowned not only for its scientific achievements but also as one of the most recognizable symbols of astronomy for the general public. It often featured on screen, shown in movies like Contact and TV shows like The X-Files as well being the location of the iconic final fight scene in the James Bond movie GoldenEye.
The dish’s massive size made it more sensitive than other radio telescopes of its era, enabling it to detect very faint radio signals and allowing researchers to peer out deeper into the cosmos than ever before.
Its early projects in SETI (the search for extraterrestrial intelligence), such as the sending of the Arecibo Message in 1974, helped bring public interest to this previously obscure field. And the telescope was instrumental in the search for the first exoplanets, as it was used to locate a pulsar around which the three earliest planets outside our solar system were discovered.
As both a practical tool of discovery and a symbol of inspiration, researchers described the decommissioning of the telescope as an “inestimable loss.”
The closure of the Arecibo telescope marks the end of an era in astronomy, astronomer and planetary scientist Franck Marchis told Digital Trends. Marchis, who studies asteroids and has worked on imaging exoplanets, is a Senior Astronomer at the SETI Institute and the Chief Scientific Officer at digital telescope company Unistellar.
The future of radio astronomy doesn’t lie in giant telescopes, Marchis said. Now, arrays or networks of multiple smaller dishes can perform the same function as a giant telescope in a more efficient manner. This is enabled by improved communication speeds, meaning data can be shared between tens or hundreds of individual antennae fast enough that they can act as a single unified telescope.
In the future, radio astronomy will be performed using facilities like the Square Kilometre Array (SKA), an intergovernmental radio telescope network planned to be built in Australia and South Africa.
“Astronomy is going from gigantic facilities like the Arecibo to distributed small facilities like SKA,” Marchis said. These facilities are less powerful than Arecibo, but they can monitor a broader field of view, collecting data on millions of stars as opposed to the narrow field of view of Arecibo which could monitor a handful of stars at a time.
The larger field of view isn’t the only advantage of arrays over single telescopes. “They’re also easier to build,” Marchis said. “It’s much easier to build 200 small antennas than to build one gigantic telescope. And they can also be upgraded easily.” That’s because it’s easier to swap out parts. The detectors used in an array might be small enough to hold in your hand, for example, while the detectors used in a giant telescope like Arecibo are the size of a house.
Another issue is how telescopes are decommissioned at the end of their lives. Small facilities can be easily dismantled when they are no longer needed, but a large facility like Arecibo will cost a huge amount to safely take apart.
“It’s sad that Arecibo is ending, because it’s a legendary telescope, it’s one of the iconic telescopes in astronomy,” Marchis said. “But it’s also it’s time. Time has changed and technology has changed. We are now more capable of doing radio astronomy with distributed small telescopes.”
This movement from large telescopes toward arrays is seen most clearly in the field of radio astronomy. But it’s starting to be seen in the field of optical astronomy as well. Although there are still large optical telescopes being built, like the European Southern Observatory’s Extremely Large Telescope in Chile, there is also a boom of distributed optical telescope networks like NASA’s asteroid-detecting ATLAS system or Marchis’s Unistellar citizen science telescope network.
There is a particular strength in inviting citizen scientists to participate in astronomy projects through more affordable and powerful home telescopes. One limitation of projects in fields like asteroid detection is that current professional networks have blind spots, for example, because the majority of astronomical surveys are based in the northern hemisphere. When citizen scientists can make observations from across the globe, the total network can gain a more complete picture of the sky, even if there’s bad weather in one location.
The diversity of locations of smaller telescopes can be beneficial in SETI projects too. Arrays like the Allen Telescope Array have traditionally searched for radio signals in the hope of identifying technosignatures of intelligent civilizations. But here on Earth, we are moving away from the use of radio waves for communication and toward the use of optical-based communications, so we can assume that technologically advanced alien civilizations would too.
The modern approach to SETI involves searching for laser signals, which would be a strong indicator of intelligent life. A distributed network of optical telescopes can follow up on potential detections to identify distinctive signals that could indicate life.
However good radio telescopes become, though, they still have to break through the background noise of interference from cell phones and other communications devices here on the ground. To get to the next level of sensitivity and to see further out into space, we need to look upwards to the sky.
For radio astronomy, “if you want to get better sensitivity, instead of building a single large dish on Earth, it would be better, if you have infinite funding, to build multiple dishes in space,” Marchis said. “I think that’s the direction that radio will take.” We likely won’t see more giant dishes being built on Earth — instead, we’ll see multiple dishes either on the ground or in space, or even on the moon.
As for optical astronomy, Marchis sees the trend heading toward smaller telescopes as well. “They’re cheaper, they’re easier to manipulate, they’re also easier to decommission,” he said. Projects like the Extremely Large Telescope may be the final marker of this era of giant telescopes. “After that, I don’t think we’re going to build something bigger.”
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