You may not believe that at this moment, a dense asteroid with a diameter of about 1 km is rapidly approaching The Earth, as fast as 19.56 kilometers per second, and will visit the Earth's orbit on January 18, 2022, with a closest distance of only 1.9776 million kilometers from the Earth, equivalent to 5.15 times the distance between the Earth and the Moon.
It is not a newly discovered asteroid, as it has been numbered (7482) 1994 PC1 by scientists. Don't panic, (7482) 1994PC1 will not hit the earth, it is said that its closest distance from the earth is 197.76 million kilometers, much farther than the moon, it is certainly a relatively safe distance.
On August 9, 1994, astronomer Robert McNaught observed through the Saidin Springs Observatory that an unknown object was approaching Earth, which was (7482) 1994 PC1. (7482) 1994 PC1 was hung with many titles, S-type asteroids, near-Earth objects, potentially dangerous asteroids, Apollo asteroids.
Why does (7482) 1994PC1 have so many titles? What exactly do these titles mean?
What is an S-type asteroid?
S-type asteroid is a stony asteroid, mainly composed of silicates of metal elements such as iron and magnesium, whether an asteroid is an S-type asteroid, the most important way to determine whether it is an Asteroid is its astronomical albedo, generally more than 0.2, the higher the albedo, the higher the densification of the stony asteroid.
About 17 percent of asteroids in the solar system are S-type asteroids, second only to carbonaceous C-type asteroids. Scientists have studied 11 S-shaped asteroids with an average density of 3 grams per cubic centimeter.
(7482) 1994PC1 has an albedo of 0.277 and is an S-type asteroid, and 0.277 indicates that it is a dense asteroid containing a large amount of metallic elements, and perhaps also contains precious metals, such as gold and silver.
What is a NEO?
There are many small bodies near the solar system, and if you want to calculate, I am afraid to use billions as the basic unit, the asteroid belt between the orbits of Mars and Jupiter, the Kuiper belt located outside the orbit of Neptune, and the Olt Nebula that surrounds the solar system, but not all of them are called near-Earth objects (NEO).
In people's view, the near-Earth object should be determined according to the closest distance between the object and the Earth, but it is not, according to NASA's convention: as long as the closest distance between a celestial body and the sun is less than 195 million kilometers, then the object is a near-Earth object.
In fact, this method of determination is very reasonable, because the sun is the center of the solar system, and the earth is rotating at a speed of 29.78 kilometers per second all the time, and the closest distance between the celestial body and the earth is constantly changing, but the closest distance between the celestial body and the sun has hardly changed.
(7482) 1994PC1 operates in an elliptical orbit with an inclination of 33 ° with a perihelion of 0.9 AU (1 AU is approximately equal to 150 million km), on the inner side of the Earth's orbit, at aphelion 1.8 AU, and on the outside of the Earth's orbit, with an orbital period of 572 days, so (7482) 1994 PC1 is a near-Earth asteroid.
What is an Apollo asteroid?
Apollo asteroids belong to the near-Earth asteroids, is a special classification of near-Earth asteroids by scientists, and named after the name Apollo in 1862, the semi-major axis of the Apollo asteroid orbit is greater than 1 AU, that is, the average distance between the Earth and the Sun, but the closest distance to the Sun is less than 1.017 AU, that is, the furthest distance between the Earth and the Sun.
As a result, Apollo asteroids often travel near Earth and are the most threatening type of celestial body to Earth, and on February 15, 2013, the meteor that exploded over the city of Chelyabinsk in southern Russia was an Apollo asteroid, injuring about 1,500 people.
(7482) 1994PC1 has an elliptical orbit of 1.8 AU*0.9 AU, which is also clearly among the Apollo asteroids.
What are potentially dangerous asteroids?
Scientists classify a subset of near-Earth asteroids that may hit Earth as potentially dangerous asteroids, and of course, there are standards for potentially dangerous asteroids.
First, the closest distance between a small near-Earth object and the Earth is less than or equal to 19.5 times the distance of the Moon (7.488 million kilometers), and second, the maximum diameter of a small near-Earth object is greater than or equal to 140 meters, because the 140-meter object enters the atmosphere and has a high chance of being preserved.
(7482) 1994PC1 is 1 km in diameter, much larger than the standard of 140 meters, (7482) 1994 PC1 is 1.9776 million km from Earth, and it is much closer than 7488,000 km, (7482) 1994 PC1 is a potentially dangerous asteroid.
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Now, it's time to know why (7482) 1994 PC1 has so many titles.
As of January 3, 2022, scientists around the world have discovered a total of 27,844 asteroids, with a cumulative number of potentially dangerous asteroids reaching 9,955, of which 889 are 1 km in diameter, and (7482) 1994PC1 asteroids are naturally included.
So the earth is not absolutely safe, to know that 65 million years ago a super comet hit the earth, creating the 5th mass extinction event, so that the former overlord dinosaurs were destroyed in an instant, which is why some people proposed an alien migration plan and asteroid defense plan, which is the so-called safe and dangerous. Interesting and informative scientific content, please pay attention to the only WeChat public account: Interesting Exploration