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Why losing Arecibo is a big problem for astronomy


Edgard Rivera-Valentin first visited the Arecibo Observatory as a child.

“I definitely remember this feeling of being impressed,” Rivera-Valentin says. "Looking at this gigantic telescope … getting to hear about all this good work that was being done … it definitely leaves an impression." An important science was happening in the back garden of Rivera-Valentin’s hometown, Arecibo, Puerto Rico, and one day, Rivera-Valentin wanted to be a part of it.

As an adult, Rivera-Valentin returned to the observatory to work as a planetary scientist, using Arecibo to map the shapes and movements of potentially dangerous asteroids close to Earth. Now, at the Lunar and Planetary Institute in Houston, Rivera-Valentin continues to use Arecibo data to study planetary surfaces. So the recent news that the Arecibo Observatory would close was "heartbreaking."

In August and November, two cables supporting a 900-tonne platform of scientific instruments on Arecibo's plate broke unexpectedly. After assessing the damage, the National Science Foundation, which funds Arecibo, announced that the telescope could not be safely repaired and shot down (SN: 19/11/20). But before the telescope could be dismantled, the entire platform of the instrument fell to the plate on December 1st.

After suffering damage in recent months, the radio telescope at the Arecibo Observatory in Puerto Rico collapsed on December 1st. The cables that suspended a platform of scientific instruments on top of the plate broke, causing the platform to fall.

For Puerto Rico, losing Arecibo is like New York losing the Empire State Building or San Francisco losing the Golden Gate Bridge, says Rivera-Valentin, but with the added tragedy that Arecibo was not just a cultural and historical icon, but a prolific investigation. installation.

“The loss of Arecibo is a great loss to the community,” says Tony Beasley, director of the National Radio Astronomy Observatory in Charlottesville, Va. "Arecibo's life cycle was really remarkable and he did an amazing science."

Radar maps from the Moon and Mars Observatory, for example, helped NASA choose the landing sites for the Apollo (SN: 5/1/65) and Viking (SN: 17/7/76) missions. And observations of the asteroid Bennu helped NASA plan its OSIRIS-REx mission to catch a sample of the space rock (SN: 21/10/20). Arecibo's views of Saturn's moon Titan revealed hydrocarbon lakes on its surface (SN: 10/1/03).

Beyond the solar system, Arecibo observed mysterious flashes of radio waves from deep space, called rapid radio bursts (SN: 2/7/20), and the distribution of galaxies in the universe. Arecibo was also used for decades in the search for extraterrestrial intelligence (SN: 11/7/92), and issued the first radio message to aliens in space in 1974 (SN: 23/11/74).

In the wake of Arecibo’s collapse, the radio astronomy community “will have to look at what was happening in Arecibo and figure out how to best replace some of those capabilities with other instruments,” Beasley says.

During its 57 years of life, the huge radio telescope of the Arecibo Observatory in Puerto Rico (shown) made important discoveries in planetary science and astronomy.University of Central Florida

But many of Arecibo’s capabilities cannot be easily replaced.

“Arecibo was unique in several ways,” says Donald Campbell, an astronomer at Cornell University and former director of the observatory. For starters, Arecibo was huge. At 305 meters wide, covering about 20 acres, Arecibo was the largest radio dish in the world since it was built in 1963 (SN: 23/11/63) until 2016, when China completed its five-hundred-foot spherical telescope. meters. or FAST. With such a huge plate to collect radio waves, Arecibo could see very weak objects and phenomena.

That incredible sensitivity made Arecibo particularly good at detecting objects that are difficult to detect such as rapidly rotating neutron stars called pulsars (SN: 1/3/20). When a pulsar rotates, it sweeps a beam of radio waves into space like a beacon, appearing to Earth like a flashing radio beacon.

Beasley says, "Arecibo was the king" of seeing the fickle light of the pulsars. "There will be no simple solution to regenerate that level of collection area." The next largest radio dish in the United States is the 100-meter-wide Green Bank Telescope in West Virginia. Smaller telescopes may require several hours of observation of a target to collect enough radio waves for analysis, while Arecibo took only minutes.

In addition to its huge size, Arecibo could also transmit radio waves. “Most radio astronomy telescopes don’t have transmitters,” Campbell says. "They're just getting radio waves from space." Radar transmitters allowed Arecibo to bounce radio waves from atmospheric gases (SN: 31/01/70), or from the surfaces of asteroids and planets. The reflected reflected signals contained information about the target such as size, shape, and movement.

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“High-power transmitters allowed what was the original primary purpose of the telescope: the study of the Earth’s ionosphere,” Campbell says. The U.S. military, which funded the construction of Arecibo, wanted to better understand the Earth's atmosphere to help develop missile defenses (SN: 2/10/68). But Arecibo’s radar transmitters “were also used to study bodies in the solar system: the planets, the moons, including our own moon,” Campbell says. “More recently, emphasis has been placed on studying asteroids close to Earth” that could be on a course of collision with Earth.

Other large radio dishes, such as China’s FAST or the Green Bank Telescope, are not equipped with radar transmitters. NASA’s Goldstone Deep Space communications complex in the Mojave Desert has a 70-meter plate with radar capability. But Goldstone "is used both as a military facility and as part of the Deep Space Network that talks to spacecraft, so it doesn't have much time," says Rivera-Valentin. “And it’s not as sensitive as Arecibo,” so you can’t see as many asteroids.

Even at the time of its demise, the Arecibo Observatory still had "a bright scientific future," says Joan Schmelz, an astronomer with the University's Space Research Association at Mountain View, California, and former deputy director of the observatory. "I didn't just rest on my laurels." For example, Arecibo was a key facility for the ongoing NANOGrav project, which uses pulsar observations to search for ripples in space-time fired by supermassive black holes (SN: 24/09/15).

Arecibo's days of observation may end, but that doesn't mean the telescope's data no longer contributes to science, Schmelz says. Some of the most exciting discoveries in radio astronomy arose from the reanalysis of ancient data from the telescope (SN: 25/07/14). "People will continue to analyze Arecibo data for some time," he says, "and we hope to see new scientific results as this data is analyzed and published."


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