If you have watched the 007 series of movies and the classic science fiction film “Contact with the Future”, you must be familiar with this scene: a large dish-shaped antenna covered in the valley with the terrain, with a large receiver hanging above it. Yes, this is the famous “Arecibo Observatory” (Arecibo Observatory).
The Science of Arecibo
Of course, only when the movie scene is definitely not its goal. Located in the Caribbean Sea of Central America, Puerto Rico, which belongs to the United States, Arecibo was completed in 1963 and was the world’s largest single-mirror telescope until China built the FAST radio telescope in 2016. With the “dish-shaped” antenna built according to the terrain, Arecibo can only scan a limited angle of the sky, but with the 305-meter-diameter antenna, it has also made many important contributions to science.
Astronomy and SETI
For astronomers, Arecibo is undoubtedly a very useful radio telescope. Many celestial bodies in space emit radio waves. From the nearest sun, planets, comets and asteroids in the solar system, to distant stars, galaxies, and inter-galactic dust, there are all examples of radio waves emitted by different physical mechanisms.
In 1974, Arecibo even discovered the “Binary pulsar”, which is a system of two relatively close neutron stars orbiting each other. In addition to the relatively strong radio wave signal, the strong gravity field also provides epoch-making progress for physicists studying gravity. Because of this discovery, the double-wave moment research won the 1993 Nobel Prize in Physics.
Another of Arecibo’s most well-known projects is probably the “Search for Extraterrestrial Civilization Project” (SETI). The SETI project is a large-scale scientific project composed of various telescopes and various scientific methods. It aims to analyze and search for signals of civilization emitted by aliens. Arecibo’s large antenna allows it to receive signals up to 200 light years away. At the same time, Arecibo is equipped with a radio wave transmitter (Transmitter), so it can also transmit earth civilization signals to space to increase the chance of finding alien civilizations.
Although SETI has not found an alien yet, it assists astronomers to receive more signals from the universe and helps to understand more deep-sky astrophysics. Arecibo is undoubtedly the protagonist of SETI, continuing to open the door to space for the earth.
Space radar
The radars we are familiar with are usually installed in military facilities, airports, and weather bureaus, and the detection targets are not too far away. Have you ever thought that the signal emitted by radar can hit space? Arecibo has this ability, allowing scientists to detect “Near-Earth objects” (NEOs) that may be harmful to the Earth for many years.
The “giant ball” suspended above the dish antenna is the receiver platform of Arecibo, which can be said to be the heart of Arecibo. The 900-ton platform is fixed by ropes from three directions and can be said to be a large suspension bridge. This is a laboratory suspended in the air. After the radio waves from the dish antenna are reflected below the platform, after a series of reflections, they are focused on different instruments.
▲ Looking up at the Arecibo receiving platform. The spherical dome in the middle is the place where various scientific instruments are placed, and the signal from the dish antenna is also focused here. The upper bracket is the machinery and support structure for moving the dome.
When Arecibo is used as a radar, the transmitter below the platform transmits radio waves to space celestial bodies and receives the reflected waves. When observing near-Earth objects, Arecibo can accurately use the Doppler effect to calculate the shape, rotation and orbit of the near-Earth objects, and most importantly, calculate how much they threaten the earth. Arecibo can be said to be the earth’s protective net.
▲ Arecibo used planetary radar to observe the near-Earth asteroid 2020 NK1 in July this year. The long and narrow shape can be seen. (Source:UCF）
Atmospheric Science
Arecibo is not only for astronomers, but also makes great contributions to atmospheric science. In fact, when Arecibo was built, scientists originally planned to focus the dish antenna on the earth’s ionosphere to quantify the earth’s atmosphere. But after completion, Arecibo was much larger than the original design, and the focus became the receiving platform, which of course was left to astronomers for research.
However, Arecibo still has many instruments for studying atmospheric sciences. By launching radio waves into the ionosphere by platform transmitters, scientists can study composition, temperature, and density, and define the boundary between the earth’s atmosphere and space. So Arecibo’s other name is “National Astronomy and Ionosphere Center” (NAIC).
Stay or not?
When Arecibo made many contributions to the scientific community, it also slowly aged. In August, the 57-year-old had an auxiliary cable break. The cable originally used to support the receiving platform hit the dish antenna below, causing the observation activity to be interrupted. Originally, scientists hoped that Arecibo could continue scientific observations after the “cable change”, but in early November a main cable was displaced and loosened, causing a huge crisis to the entire structure supporting the receiving platform.
At this time, the scientific and astronomical community began to debate the fate of Arecibo. Astronomers who hope it can continue to observe will bring out the brilliant research results in the past, and the observation of near-Earth objects is even more important data. But in reality, the repair of Arecibo and the replacement of cables are really time-consuming and costly. The US government has also lost interest in the 57-year-old middle-aged telescope, and instead invests more funds in newer and more promising ones. equipment.
Destruction of Arecibo
Finally, on November 19th, the National Science Foundation officially announced that Arecibo will be decommissioned, and the supporting cables and receiving platforms with structural problems will be removed in stages.
But no one thought that at 7 o’clock in the morning on December 1st, a loud bang broke the peace of the morning. The remaining cables supporting the platform broke in response, and the entire receiving platform, the 900-ton heart and a cable tower slammed into the dish antenna below. Although the damage caused is still being evaluated, the photos and videos still shock everyone.
▲ The film when Arecibo collapsed.
After losing Arecibo?
Of course, after assessing the extent of this damage, I sincerely hope that some auxiliary equipment and instruments will survive and continue or transfer to other telescopes. Fortunately, the control room, visitor center, and museum next to the dish antenna were unharmed, and there were no casualties immediately after the collapse.
Thankfully, Arecibo is not the only telescope that can monitor near-Earth objects. The major astronomical telescopes on the surface and the artificial satellites of various countries are still spreading the net, hoping to detect any celestial bodies threatening the earth as soon as possible. China’s FAST project and the future advanced astronomical telescopes of other countries are undoubtedly capable of performing various scientific tasks in Arecibo.
But what should be more introspective is that the “old age” scientific projects and equipment should be decommissioned as soon as possible, or should they be “upgraded” as soon as possible? If the funding of the scientific research project is fixed, how much should be devoted to “ageing” and how much should be devoted to “assisting youth”? All kinds of problems are testing the government organizations with funds and scientists with research experience.
As for you and me, you can think about it. Scientific research projects and instruments are not easy to come by. When hardware is like human life and death, do you cherish it in time?
(The first picture is an aerial shot of Arecibo. Above the dish antenna is the receiving platform suspended by ropes, and the building on the right is the control room and visitor center. Picture source:Arecibo Observatory）
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