At 5:23 a.m. Beijing time on March 12, an asteroid 2022 EB5 with a diameter of about 2 meters broke into the Earth's atmosphere and exploded over the waters near Iceland. This is the fifth time in human history that an early warning asteroid intrusion has been detected by the U.S. telescope system, the first four by the U.S. telescope system, this time by the Pisces Observatory in Hungary, designated K88.
So, how did the asteroid intrusion warning come about? We asked Li Mingtao, a researcher at the National Space Science Center of the Chinese Academy of Sciences, to introduce himself to you.
A little luck in the discovery
On March 11, 2022, on a very mundane evening at the Pisces Observatory near Budapest, Hungary, astronomer Christian Sarnetsky prepared to begin an all-night sky survey at 7 p.m. local time. His goal is to find dangerous asteroids that come from space.
It's a job that requires a little bit of luck. Because astronomers don't know when and from which direction these "little dots" of the solar system will fly over. So Christian Sarnetsky could only divide the night sky into small lattices, like a chessboard or a fishing net, and then use his telescope to scan these "mesh holes" one by one. If he's lucky, he'll find a moving asteroid in this region, and if he's lucky enough to spot it before another telescope, he'll have the right to name it.
This is not easy, because his equipment is a 0.6-meter aperture Schmidt telescope. A key measure of a telescope's observation capabilities is its aperture, which is larger and more capable of collecting light, and the fainter asteroids can be found farther away. Compared with the Catalina Sky Survey System of the United States (3 telescopes, the maximum aperture of 1.5 meters, the annual discovery volume of the world's first), the Pan-Star Program telescope system (2 telescopes, aperture of 1.8 meters, the second largest annual discovery in the world) and the Earth impact proximity warning system (4 telescopes, aperture of 0.6 meters, the third in the world in the annual discovery), the telescope of Pisces Observatory does not have an advantage in terms of observation aperture. But it's not entirely without opportunity, as U.S. telescopes are largely deployed on the U.S. mainland and on the island of Hawaii in the Pacific Ocean. The Pisces Observatory is located in Eastern Europe and is geographically located to make "relay" observations with the United States.
For example, at this time, the telescopes in the United States and Hawaii Island were still in daylight. Even the most powerful optical telescopes can only "lie down" during the day, because the dazzling sunlight during the day will drown out the asteroid's very weak signal, just as we can't see the stars during the day, and the optical telescope can't see the asteroid during the day. Most of the "large" large asteroids were discovered in advance by large telescopes in the United States at great distances, but there are always some small sizes that have slipped through the net. These "little guys" are so small that the sunlight they reflect is too dim and weak to be seen by telescopes only before they are close to Earth. American telescopes sleep through the day, and this is a great opportunity for the Pisces Observatory to play a role!
After all, there are not many such asteroids, and Christian Sarnetsky did not expect much. As usual, he made observation plans, scanning the celestial grids one by one. At 8:24 a.m. local time (7:24 GMT), he spotted a moving target of about 17 magnitude stars in brightness— a "fish" hooked. Christian Sarnetsky was well aware of the speed at which the "fish" was moving, and years of observational experience had convinced him that once the "fish" bit the hook, it was impossible for the "fish" to escape from the "fishing net", so he did not interrupt the observation plan, but let the telescope continue to scan the back of the sky grid.
Half an hour later, Christian Sarnetsky completed the scheduled observation plan. When he mobilized the telescope to find the "fish" again, he was surprised to find that the "fish" was missing. Could it be that this "fish" swims particularly fast? Christian Sarnetsky soon spotted the "fish" in the northern sky area where it was originally intended, along with its "wake" as it swam through the sky. Obviously, this is not an ordinary "fish", something that Christian Sarnetsky has not discovered in his years of observation. This "fish" apparently swims faster than most asteroids.
Christian Sarnetsky initially thought that this was an artificial object, perhaps the last stage of an abandoned rocket running in earth's large elliptical orbit, otherwise it would not have been able to "swim" so fast! Then, however, an incredible thought came to his mind: Could this be an asteroid about to hit Earth? If it wasn't an artificial object, it would have to be an asteroid about to hit Earth. Because only an asteroid that is about to hit Earth can move so fast!
Christian Sarnetsky enters the coordinates of the telescope observations into the orbit calculation software. Software Tip: Crash! 21:22 GMT on March 11, 2022 at 70.263° N and 9.88809° W. That is, it is only 1 and a half hours before the asteroid hits the Earth!
Pisces Observatory in Budapest, Hungary
Successfully triggered an early warning after a wave of twists and turns
Christian Sarnetsky has dreamed countless times that one day he will discover an asteroid that hits Earth, but he never believes he can really do it.
Judging by brightness and speed, the asteroid may be only a few meters, will ablate and disintegrate in the atmosphere, and will not pose any threat to humans. This is also the fifth time in human history that an asteroid intrusion has been warned of before the asteroid crashes into the Earth. The previous four were 2008 TC3, 2014 AA, 2018 LA and 2019 MO, all discovered by the U.S. telescope. It took at least 8 hours from discovery to impact on Earth. But this time it was only two hours, and if you exclude the half hour spent confirming the asteroid, it is only 1.5 hours.
Christian Sarnetsky was so excited that he had uploaded the data to the International Minor Planet Center's Objects for Confirmation page. The International Minor Planet Center, an institution supported by the International Astronomical Society and operating on the Smithsonian Astrophysics Observatory at Harvard University, is the data hub for global asteroid observations, which is responsible for collecting global observation data and guiding global observers to track and measure newly discovered asteroids in order to determine the orbit of the asteroid as soon as possible. At the same time, he also tried to send observational data to the asteroid observation community in order to inform international observation peers of this "big event" as soon as possible. In a hurry, he wrote the wrong email address, and the email was not sent to the asteroid observation community.
Fortunately, the data that Christian Sarnetsky uploaded to the International Minor Planet Center triggered the European Space Agency's SeaCat Asteroid Impact Assessment System and NASA's Scout Asteroid Impact Assessment System. According to the first 4 observations, the probability of the asteroid hitting Earth is about 1%. An hour later, at 20:25 GMT, Christian Sarnetsky uploaded 10 of the latest observations, and the probability of impact rose to 100%. After officially confirming that the asteroid would hit The Earth's atmosphere, the SeaCat system sent the alert message to the European Near-Earth Celestial Coordination Center, and the Scout system informed NASA's Center for Near-Earth Objects research and the Planetary Defense Coordination Office.
The Scout system expects the asteroid to fall in the ocean 140 km southwest of the Norwegian island of Jan meyer at 21:23 GMT, and subsequent ultrasonic sensor observations have confirmed the time and site of impact. The site of the explosion was in the no-man's land of the ocean, so no optical information was obtained.
According to optical and ultrasonic observations, the asteroid is about 2 meters in size and the energy of the impact on Earth is equivalent to about 4,000 tons of TNT explosives. Since most of the energy is released at high altitudes through disintegration explosions, the asteroid has not caused any damage to life and property on Earth. Eventually, the asteroid was named 2022 EB5, which is the fifth successful warning of an asteroid impact event in Europe and the first time in Europe that an asteroid has struck earth.
The number of such 2-meter-sized asteroids is extremely large, and it may hit the Earth every month, forming a dazzling fire meteor event. Due to their small size and dim brightness, they are often only found with optical telescopes a few hours before they are close to Earth. However, such asteroids are not very dangerous. The field of planetary defense is mainly concerned with near-Earth asteroids with an equivalent diameter of tens of meters or more.
Don't know
How to break the blind spot of asteroid warning?
So, what is the world doing to prevent the attack of near-Earth asteroids?
The equivalent near-Earth asteroids with a diameter greater than 140 meters can cause regional-level hazards when hitting the Earth, with a theoretical number of about 24,000 and a discovery completion rate of about 40%. Relying on advanced ground-based optical telescopes can monitor such large-sized asteroids in advance at a distance of hundreds of millions of kilometers, they can be long-term early warning through census cataloging, and the warning time can reach grades, tenth grades or even centenarian grades. After the discovery of such asteroids, they can be tracked and measured by optical telescopes and radar, determine their high-precision orbital data information, and calculate the probability of the asteroid hitting the earth, that is, the probability of impact. Combining spectral and radar measurements of the asteroid, the asteroid's material type (carbonaceous, rocky and metallic) is inferred to further assess its hazard level to support the implementation of effective on-orbit disposal.
Near-Earth asteroids with a diameter of tens of meters, the impact area can cause town-level and even large-scale city-level hazards, and its theoretical number is as high as millions, and the current number of discoveries is less than 3%. Due to its large number and weak reflection, it is difficult to catalog all its censuses in a short period of time. Therefore, a proximity warning system should be developed to build a proximity alarm circle within a certain distance (such as 7.5 million kilometers) before the small asteroid hits the earth, and implement the proximity alarm to support the evacuation of the ground population and the implementation of effective rescue.
Due to the influence of atmosphere, light and other factors, ground-based optical telescopes cannot observe asteroids from the daytime direction, and there is an early warning blind spot in the daytime direction. Space-based monitoring has the advantage of all-day, all-weather, and by optimizing deep space orbits, it can provide an effective means of early warning of ground-based blind asteroids. Recently, Chinese researchers published an article in Icarus, a well-known journal in the field of planetary science, proposing to deploy telescopes about 10 million kilometers in front of the Earth's orbit to escort the Earth in front of the Earth, and to warn in advance of small asteroids that hit the Earth from the direction of daytime.
On April 24, 2021, at the opening ceremony of China Space Day, Zhang Kejian, director of the China National Space Administration, pointed out in his speech that facing the future, China will build a near-Earth asteroid defense system. It is believed that in the future, China will contribute more Chinese wisdom, Chinese solutions and Chinese strength to early warning and handling the threat of near-Earth asteroid impacts.