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December 3 Beijing time news, according to foreign media reports, you may be happy if you don’t know that danger is coming; And planning ahead can improve your chances of survival when danger strikes.But in terms of planetary defense, knowing that danger is approaching, it is inevitable.
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The Arecibo telescope captured radar data from an asteroid named Phaethon in December 2017
Planetary defense is the art of identifying and mitigating the threat of asteroids hitting the earth. One of the tools used in planetary defense is called planetary radar. Planetary radar is very special, it allows scientists to better observe nearby celestial bodies. The Arecibo telescope in Puerto Rico is one of the few planetary radars on Earth. This year, Arecibo experienced two serious cable accidents. The National Science Foundation (NSF), which owns the site, said that after the accident, the structure of the telescope was very unstable, and even the staff could not safely assess the state of the telescope. Therefore, NASA decided to dismantle the facility.
However, in terms of planetary defense, no one can match the Arecibo telescope.
“There are reports that ‘we have other facilities that can replace Arecibo,’ but I don’t think that’s necessarily the case,” said Anne Waukey. He was responsible for the planetary radar equipment of the Arecibo telescope. Waukee said: “It is not outdated and cannot be easily replaced by other existing installations.”
Planetary defense begins by discovering as many near-Earth asteroids as possible (according to NASA, 25,000 near-Earth asteroids have been discovered so far) and estimating the size and orbit of the asteroid around the sun. The Arecibo telescope has never played a role in the discovery of asteroids; other telescopes (like the PanSTARRS Observatory in Hawaii) that can observe large areas of the sky under visible and infrared light and have the ability to capture sudden bright spots between stars. The task of discovering asteroids can be completed more easily. Through these first-hand observations, scientists can mark the smallest asteroids and asteroids farther from Earth, which are not to be feared.
However, the larger planets that orbit closer to Earth require more research on them. Usually this is the work of the Arecibo telescope. The Arecibo telescope is equipped with a powerful radar transmitter and the emitted light beam can be reflected from the surface of near-Earth celestial bodies. The large butterfly antenna of the telescope can capture the echo of the signal. Based on this data, scientists can decipher the precise details of the asteroid’s position, size, shape, and surface conditions.
Telescopes that discovered asteroids for the first time can also provide scientists with this data to track the orbits of space rocks. But planetary radar can complete data collection faster by discovering celestial bodies.
Bruce Bates, the chief scientist at the nonprofit space exploration advocacy organization Planetary Society, says that sometimes speed is everything. “It is necessary to calculate the orbit of the asteroid as quickly as possible to determine if it will hit Earth.”
With enough warnings, humans can theoretically take certain measures to avoid asteroid collisions – for example, pushing asteroids out of orbit or breaking them into smaller pieces to reduce damage to the earth’s surface.
Bates said: “If we work hard enough, an asteroid hitting Earth is actually a preventable natural disaster. Although this rarely happens, it is actually controllable and not as inevitable as a hurricane or earthquake.”
Radar can provide more details about space rocks and provide information for planetary defense, including key information such as whether the asteroid is a single celestial body or a binary system disguised as a single celestial body. It turns out that 15% of near-Earth asteroids are binary systems that look like a single celestial body. Bates said, “Obviously, if you intend to deviate the orbit of an asteroid, then you must know whether the asteroid is a single celestial body or contains two celestial bodies.”
Information about the composition of space rocks is also important. “Some are solid metals, some are spongy spheres or piles of gravel, so their density is quite different.” Bates said: “If this asteroid is coming straight towards Earth, if you have to deviate its orbit, then the countermeasures that are taken will depend on whether it is a dense asteroid or a fluffy asteroid.”
Therefore, radar is very important to our planet.
Of course, the Arecibo telescope is not the only radar installation. But the expensive technology equipped with the Arecibo telescope gives it extraordinary capabilities. After the loss of the Arecibo telescope, the only remaining radar transmitter is located in the Jinshi Deep Space Communication Center operated by NASA’s Jet Propulsion Laboratory in California. But the facility already has many other responsibilities. It is part of the deep space network (the deep space network is responsible for communications with spacecraft within the solar system) and also conducts military missions.
“When arranging to observe the recently discovered target, other facilities are not as flexible as Arecibo.” Waukey said: “If the target observation data is not available in time during the target observation period, I soon lost the opportunity to observe. Then the uncertainty of these asteroids in their orbits will be greater.” The difference between this uncertainty is whether you are concerned that the space rock will hit the ground or you are sure it won’t hit the ground.
Waukee also said that the sensitivity of the Jinshi radar system is about 20 times lower than that of Arecibo, and the observing space of the two systems is different. “Therefore, the Jinshi facilities cannot completely replace the Arecibo telescope.”
Waukee said there are also plans to add a radar system to the Greenbank Telescope in West Virginia. However, Waukee emphasized again that even so, the Greenbank telescope cannot replace Arecibo. He said the Greenbank telescope will use slightly different radar than the Arecibo telescope and will be more susceptible to weather.
Additionally, the Greenbank telescope’s beam is relatively narrow, limiting Greenbank’s ability to track asteroids. “If the beam is relatively narrow, then you have to be very clear about the direction of the radar.” Waukey said, “With a narrow beam, you can’t look around.” But Arecibo can better track asteroids with uncertain orbits.
Former NASA astronaut Ed Lu is now the executive director of the B612 Asteroid Institute, a non-profit organization that focuses on asteroid science and migration research. He said that all of the above factors mean that the loss of Arecibo has greatly affected the planetary defense capabilities on Earth. “This is a huge loss for planetary defense,” he said, “although it will not completely lose planetary defense capabilities, it will definitely be affected.”
Of course, there are other risks. Bates said: “The radar system is very complicated and occasional failures are not impossible. But after losing Arecibo, we now have no redundancy in our system. Once Jinshi’s radar fails, we have no other system to replace. Yes Jinshi’s radar fails at the wrong time, the missed opportunity will be lost forever. “
Ed Lu said that for planetary defense experts, this risk is compounded. He said that the discovery of new asteroids is getting faster and faster, and when the Willa Rubin Observatory goes live next year, the discovery of asteroids will be faster and faster.
Speaking of the Vera Rubin Observatory, Lu said: “The number of asteroids discovered by this observatory will be ten times that of all other telescopes. We will have a large number of new asteroids to observe, many of which will be very close. Earth, and we don’t know if they will hit Earth. “
The risk of impact has not changed. But while the ability to discover asteroids has improved, it has lost the ability to define asteroids, which means greater uncertainty.
The three experts also agreed that, at the moment, the Arecibo telescope’s radar capabilities cannot be easily replaced.
“Before, we used to think of ways to repair Arecibo, rebuild Arecibo or even improve Arecibo.” Lu said: “Although this requires a lot of money, but now because we did not invest as soon as possible, Arecibo The Bo telescope collapsed. We knew we would regret it some day in the future, but we did not expect that day to come so soon.” (Yun Lin)
