Shulou(Shulou.com)11/24 Report--

When will the asteroid hit the earth? This has always been an issue of concern, especially when we know that the previous resident of the earth died of an asteroid.

Fig. 1 NASA in Yucatan Peninsula in fact, the earth is attacked by a number of celestial bodies every day, most of which have been lost in friction with the earth's atmosphere, making it difficult to reach the earth's surface. For the visible and non-threatening part, people also have a romantic name-meteor shower. Obviously, when you are not threatening, even if you open your teeth and claws is just cute.

What if there's a threat? On March 24, 1993, astronomers observed a comet called Shoemaker-Levy 9 (D / 1993 F2purd D is a missing or disintegrated comet, 1993 is the year, F is the second half of March). By the time it was discovered, Shoemaker-Levy 9 had been captured by Jupiter and had been dismembered into 21 pieces. Astronomers calculated that the comet would hit Jupiter in July 1994. Astronomers have not yet seen the impact of celestial bodies in the solar system, so this prediction soon became a hot search in the astronomical community.

Fig. 2 A giant black spot left by the impact (NASA) 20:00 GMT, July 16, 1994, these fragments crashed into Jupiter at a speed of 210,000 kilometers per hour, the largest of which, the G impact, created a giant black spot nearly the diameter of the Earth, generating energy equivalent to 600 times the energy of human nuclear weapons.

The follow-up study brings you good news and bad news. The good news is that gaseous giants such as Jupiter and Saturn reduce the possibility of outer solar system objects entering the inner solar system and act as bodyguards for Earth. The bad news is that Shoemaker-Levy 9 is about 1.8 kilometers in diameter, and such objects can be found everywhere in the solar system. There are more than 2000 potentially dangerous objects (PHO) with a distance of less than 0.05 astronomical units from the intersection of the Earth's minimum orbit alone, of which more than 150 are more than 1 km in diameter. However, in recent years, human beings have done a lot of research on the orbital data of these celestial bodies, and through the monitoring of these celestial bodies, the security of human civilization can obviously be improved.

Fig. 3 orbit of potentially dangerous asteroids (NASA) however, existing methods tend to find objects outside the Earth's orbit because they are easy to be found in the night sky. There is a prerequisite that the semi-major axis of their orbit is larger than the radius of the earth's orbit, otherwise the possibility of observation will be greatly reduced. Because of this, the observation of celestial bodies in Earth's orbit has been slow, and only 25 have been found so far.

Fig. 4 recently, astronomers have discovered three more near-Earth asteroids hidden in the sun, which have not been discovered by humans. The three asteroids orbit between Earth and Venus, and astronomers can only observe them for a short 10 minutes in the early morning and evening in order to avoid the bright light of the sun. By observing the 624-square-degree sky near and inside Venus, astronomers finally found that two of the three NEOs (2021 LJ4, 2021 PH27 and 2022 AP7) may be more than 1 kilometer in diameter. If they hit the Earth, we can enjoy the same treatment as the previous resident of Earth.

Specifically, what are the characteristics of these three celestial bodies?

2022 AP7 is the largest of the three celestial bodies, and unfortunately, it is also the one most likely to become an assassin on Earth. Only 0.0475AU (astronomical unit) is the minimum orbital intersection distance of 2022 AP7, which makes it a veritable potential threat object and the largest potential threat object discovered in the past eight years. And it is likely to rank in the top 5% of the known potential threat objects. It seems that astronomers accidentally found a big guy. By comparing past data, the researchers found that the object had been observed before, but it was dim at the time, perhaps because it coincided with the Earth's orbit or for other reasons, all in all recently discovered. Its findings also show the effectiveness of the Twilight survey, there may be many 2022 AP7-like objects, hidden in the sun and large, we need more research to rule out such a threat.

The orbits of 2021 LJ4 and 2021 PH27 are safer and do not pose a threat to Earth, but astronomers are still interested in 2021 PH27 because it is the closest known asteroid to the sun. The perihelion of 2021 PH27 has only 0.133 astronomical units, which makes it have a greater general relativistic effect than any known object in the solar system, about 53 angular seconds per century, far exceeding Mercury's 43 angular seconds.

However, the effect of general relativity is not important in the orbital evolution of 2021 PH27, more important is the force of planetary perturbation, because it passes through the orbit of Venus, and the minimum orbital intersection is only 0.015AU from Venus, which makes it a potential threat to Venus.

The numerical simulation of the future 100,000-year orbit of 2021 PH27 shows that 2021 PH27 will become more and more unstable and will come into close contact with Venus many times and enter the Hill sphere of Venus (the region where celestial bodies dominate the attraction of the moon), in which the possibility of hitting Venus is not ruled out. Over time, the coupling of eccentricity and inclination indicates that 2021 PH27 is experiencing a resonant interaction with Venus. If 2021 PH27 is an active asteroid, it may produce meteor showers in Venus's atmosphere, and readers living in Venus will be able to see this scene.

In addition, 2021 PH27 can reach a surface temperature of about 500 °C when it is closest to the sun. This temperature far exceeds the melting point of lead, which indicates that the surface of the celestial body has undergone strong heat treatment changes, and the internal structure may also be affected by this thermal change, but the details can only be known through follow-up observation and calculation.

Obviously, it is necessary to observe an asteroid at twilight, but it is still difficult. In addition to the extremely short observation window, the thick atmosphere near the horizon also poses a challenge to the observation. And such observations cannot be carried out in space, because space telescopes are afraid of sunlight burning parts. How to better catch these Earth assassins, we can only look forward to the next step of astronomers' efforts.

reference

Https://hubblesite.org/contents/media/images/1994/34/179-Image.html

Http://www.physics.sfasu.edu/astro/sl9/cometfaq2.html#Q3.1

Https://www.jpl.nasa.gov/asteroid-watch

Solem J C. Density and size of Comet Shoemaker-Levy 9 deduced from a tidal breakup model [J]. Nature, 1994 (6488): 349-351.

Sheppard S S, Tholen D J, Pokorn arrow P, et al. A deep and wide twilight survey for asteroids interior to earth and venus [J]. The Astronomical Journal, 2022 (4): 168.

Carbognani A, Tanga P, Bernardi F. Is 2021 PH27 an active asteroid with a meteor shower detectable on Venus? [J]. Monthly Notices of the Royal Astronomical Society: Letters, 2022: L40-L44.

This article comes from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone), author: Xing Si

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.