“If an asteroid hits Earth, it causes damage tens of thousands of times the size of an atomic bomb!” News and newspaper articles with this title appear several times a year. Some people look at these articles and contact the Korea Astronomical Research Institute to confirm the facts. On the other hand, some people who have been deceived by the’shepherd boy’ every time may try not to believe without checking the authenticity. But will the asteroid really hit Earth? Through an asteroid orbit analysis program called NASA, it automatically calculates the probability of a collision with Earth for the next 100 years for all 25,000 near-earth asteroids discovered by humans so far.
According to the calculation results, the asteroid with the highest probability of collision as of March 2021 is a celestial object with the name ‘2010 RF12’ (temporary number), and the probability of collision on September 5, 2095 is 4.6%. The second-highest asteroid ‘2017 WT28’ has a 1.1% probability of colliding with Earth on November 24, 2104, and the third is an asteroid named ‘2020 VW’ with a probability of colliding with Earth on November 2, 2074 of 0.37%.
The probability of asteroid hitting Earth is low
Just looking at these three cases confirms that the probability of an asteroid impacting Earth is extremely low. In addition, the orbits of the asteroids become more precise through continuous follow-up observations after they are first discovered, and the four digits in front of the names (temporary numbers) of these three asteroids are the year of discovery. In other words, since they are the first asteroids discovered in 2010, 2017, and 2020, respectively, the probability of collision will change as additional observations proceed. But nevertheless, even if they hit the earth, there would be little damage. This is because each size is only about 7m, 8m, and 7m in diameter. Even if a small asteroid of this size collides with Earth, most of it will disappear from the atmosphere and some will fall in the form of meteorites.
Therefore, NASA defines an asteroid with a diameter of 140 m or more, which can cause serious disasters in an area of several hundred kilometers if it collides with the Earth, rather than such a small-sized asteroid, and is separately tracked and managed. As of March 2021, there are a total of 2174 terrestrial asteroids discovered, of which 4 are all objects with a higher probability of impacting the Earth in the next 100 years than 1 in 1 million. In the order of the highest cumulative collision probability, the NASA Osiris-Rex probe’s mission target asteroids Benu (0.037%), 1950 DA (0.012%), and the latest 0.1AU (AU is the average distance between the Earth and the Sun, about 149.59 million). They traveled safely at a distance of 7870.7km), but in 2029, Apophis (0.00045%) and the 2007 FT3 (0.00014%) asteroid that will approach the depths of geostationary satellites (36,000km) are these.
If so, can we really be relieved?
On February 15, 2013, an asteroid about 17 to 20 meters in diameter collided in Chelyabinsk, Russia. In the impact of the explosion, 1,600 people were injured and 7,300 buildings were damaged. The explosive energy was estimated to be about 400 to 600 kilotons (Kt·1000 tons) of the TNT bomb. NASA’s sentry calculation program, mentioned earlier, missed this Chelyabinsk collision asteroid because it did not find it beforehand. Then, why couldn’t the asteroid that fell in Chelyabinsk, Russia that day, couldn’t be found in advance?
Firstly, it is very small in size. Asteroids are celestial bodies that do not emit light by themselves and are observed by reflecting sunlight.The average reflectance of stone asteroids (asteroids mainly composed of iron silicate and magnesium silicate), which is most distributed in space near the earth, is in visible light. It is only about 15%. In other words, it is difficult to find the Chelyabinsk asteroid, which is estimated to be 17 to 20 meters long, with a telescope until it is very close to Earth. The second reason is that the path to the asteroid’s atmosphere was near the sun. Except for the solar telescope, it is almost impossible to navigate the area near the sun with any telescope on the earth at this time. To overcome this problem, NASA has been promoting the development of a space telescope dedicated to asteroid exploration that explores the vicinity of the Earth at the’L1 point of Lagrange’ between the Earth and the Sun from several years ago.
Mankind’s awareness of the asteroid-earth impact is not just a’distant story’ of the destruction of dinosaurs in the past, but the fact that an asteroid impact can be divided between before and after the asteroid explosion in Chelyabinsk, Russia on February 15, 2013. It gave a great shock that it was a’event that can happen anytime in the 21st century’ in which I live. Taking this opportunity, the international community has created an International Asteroid Warning Network (IAWN), centered on the United Nations (UN), for early detection of near-earth asteroids and establishing an international tracking and observation cooperation system.
Will you look at the asteroid only as an object of fear?
The greater value of the asteroid lies in its being a living fossil of the solar system. Asteroids, a collection of planetesimals that have not been able to grow into planets in the early stages of solar system formation, have clues that can infer the appearance of the early solar system. Just as fossils tell us that dinosaurs lived on Earth in the past, we can look into the past of our solar system through asteroids.
In December 2020, the Japan Aerospace Research and Development Organization’s (JAXA) Hayabusa-2 probe collects surface material from the asteroid Ryugu and returns to Earth, and several probes, including NASA’s Osiris-Rex, are visiting the asteroid. It is scheduled to visit, and Europe, China, and Taiwan are also vying for asteroid exploration because asteroids are treasure-like objects that hold the key to evolution that connects the past, present and future of the solar system. At the same time, it contains rare minerals of high value as future resource utilization. Due to the nature of their orbit, near-Earth asteroids periodically approach Earth or encounter Earth’s orbit. In other words, the fact that the asteroid’s orbit is similar to that of the Earth’s orbit means that it is a good condition for the probe to reach the asteroid even with less fuel. As such, we hope that Korea will soon be able to participate in the exploration of asteroids that are both sides of a coin and a double-edged sword.
√ Please remember
Kim Myung-jin Senior Researcher, Korea Astronomy Research Institute
So far, all 25,000 near-Earth asteroids discovered by humans have the highest probability of a collision with Earth over the next 100 years at 4.6%. Of the asteroids with a diameter of 140 m or more that can cause serious disaster if they collide with the Earth, there are all 4 objects with a collision probability of more than 1 in 1 million. However, the asteroid that crashed in Chelyabinsk, Russia in 2013 and destroyed more than 7300 buildings, was small and could not be found by approaching orbiting near the sun.