Recently, an asteroid numbered 2022 AP7 was noticed by the marketing number (don't), and then, unsurprisingly, it was pulled out of the video with the eye-catching headline "or threaten Earth, possibly cause mass extinction".
I hate the word "or" in marketing numbers and some media, and if you add this word, you can run the train with your mouth full.
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Well, let's start with a quick word about the asteroid: it won't hit, it won't hit, it won't hit.
A little more rigorous: for at least 300 years, it has no hope of coming near us. We'll talk about why in a moment, this asteroid is quite interesting.
A little more: hundreds or even thousands of years later, it may have a little slim chance, and we care more about those students who are more advanced (shā) tu (qì), okay?
01
Why did this asteroid become a "net celebrity"?
So many asteroids can be found every year, why did the marketing number target it? The idea of the marketing number is difficult to guess, but if you look at it, there are about these reasons:
First, the 2022 AP7 was discovered through the dark energy sky survey equipment, which seems to be noble and bizarre. In fact, things are commonplace: the dark energy telescope (DECam) has the largest field of view in the same aperture device, so it is used as a side business to discover small solar system objects. And the asteroid itself has nothing to do with dark energy.
Second, it was discovered during the investigation of small celestial bodies whose orbits can reach between Venus and Earth. This type of small celestial body has a common feature, that is, it is often hidden in the twilight, and once discovered, it makes people break out in a cold sweat. Indeed, sneaking up on the sun under the cover of the sun's brilliance is the most frightening. The bolide that hit Chelyabinsk in 2013 came from the direction of the sun and no one knew about it beforehand.
Third, the asteroid is very large, on the order of kilometers, if it is given a chance to hit the Earth, it is indeed enough to cause mass extinction. According to discoverer Scott Sheppard, it should be in the top five percent of known near-Earth asteroids.
The closest distance between the asteroid's orbit and the Earth's orbit is 0.047 astronomical units (that is, the mean distance between the Sun and Earth, abbreviated as AU), or more sensibly, 19 Earth-Moon distances, falling within 0.05 AU of the potential threat asteroid judgment index.
5. English reading comprehension. Sheppard's paper originally read: 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. (Of the discoveries made in the last 8 years, 2022 AP7 should be the largest potentially threatening asteroid) "the largest potentially hazardous asteroid" here is likely to be understood (deliberately) as "potentially the most threatening asteroid."
Now, let's talk about why the industry doesn't take this asteroid seriously.
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02
Is this asteroid really dangerous?
2022 AP7 is classified as a "potential threat asteroid" because of its large size and closest to Earth's orbit falling within 0.05 AU. But close orbit does not mean that the celestial body is close, and when we run to the orbital rendezvous, 2022 AP7 is not there; When it came to the meeting point, the earth went far away. When it was closest to Earth in March 2022, it was 1.5 AU away. What is this like? Just like the Beijing-Guangzhou Line and the Longhai Line meet in Zhengzhou, the train that has just sent from Beijing to Zhengzhou will definitely not meet the train that is going from Zhengzhou to Lanzhou, and the train from Lanzhou to Zhengzhou will not meet the train from Zhengzhou to Beijing.
You might say: quibbles! Each has its own orbital period, and one day, Earth and 2022 AP7 will meet near the closest point of their orbits. Just like the trains on the two lines just mentioned, as long as they do not deliberately hide from each other, each of them continues to go back and forth on their own lines, and there will always be times when they meet in Zhengzhou.
This makes good sense, but this asteroid is really fun, its orbital period is a full 5 years, every 5 years, it will return to the same position as the Earth, that is, since it missed the Earth this year, then after 5 years, it will miss it again, and so on.
This integer-multiple orbital relationship makes it and the Earth repeatedly flutter each other, which is very difficult to threaten us. Think about it: If a killer comes to your door every five days, and you happen to spend the night at the unit every day, the killer only deserves to shoot the "Stupid Thief Basket" series.
In summary, calculations show that the asteroid's distance from Earth will not be shorter than 1 AU in 300 years. In fact, what about shorter than 1AU? A distance between the sun and the earth, even the light has to walk 500 seconds!
So why do we say that it may have a chance in the future? Science, as long as the probability is not a solid 0, you have to say "possible". It's just that when the marketing number says "or", we want you to believe that it is 100%, and when we say "or", we want everyone to understand that it is basically equal to 0%.
Let's start by saying: even if there is a chance, it is not given to it alone. There are so many small celestial bodies that can threaten the earth, if even a stupid thief like 2022 AP7 has a chance, other players have a better chance.
This opportunity is celestial perturbation. If an asteroid walks to the side of a larger object, its orbit may shift due to gravity. If the orbital period of 2022 AP7 and the Earth is no longer accurate 5:1, it will have a chance to hit us as it travels in and out of Earth's orbit. Calculations show that it is 0.16 AU from Mars in 2107 and can run to 1.2 AU from Jupiter in 2109, which may be perturbed by these planets, causing orbital shifts. But the mass of Mars is very small, although Jupiter is fat, 1.2AU is still too far away, so the chance of these "big guys" changing their fate is very slim, we just simply say in a mathematical sense "no matter how slim it is".
In order to prevent the marketing number from being taken out of context, we reiterate once again: the opportunity is not just for it, nor that it will never hit the Earth, but that there are better talented Earth killers in the solar system. Asteroids with a closest distance of less than 0.0004 AU from Earth orbit and no integer multiple orbital period, can count more than 20, 2022 AP7 really does not count.
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In short, the 2022 AP7 is a very funny killer, and I suspect that the marketing number is trying to get everyone to pay attention to it and have a good laugh. Without talking about it, let's talk about some practical progress in near-Earth asteroid defense!
03
Do we have a move in the face of asteroids?
The topic of asteroid defense, we have talked about some in the past, readers can read it first: human beings should thank asteroids for their "grace not to kill", but they must be able to blow them up!
Recently, NASA performed a near-Earth asteroid defense rehearsal, which was very successful. This project is called DART, and we'll talk about the highlights of this mission.
Let's start with the abbreviation DART, which stands for Double Asteroid Redirection Test, which contains two key pieces of information.
First, this is a means of changing the orbit of an asteroid by impacting to avoid an attack on Earth, not the bombardment of nuclear weapons that science fiction blockbusters like to use.
Second, the test target is a binary asteroid system, and the smaller one is to be hit. The advantages of this selection of targets are twofold: First, by measuring the orbital period of the two asteroids after impact, the effect of the experiment can be easily judged. Second, there are large people who control the overall direction of operation, and even if the experimental effect is unexpected, it will not change the overall orbit of this small system, so as not to knock the otherwise harmless celestial body into a potential killer.
In this binary asteroid system, the big guy is called Didymos and the little guy is called Dimorphos, let's call them Big D and Little D. Big D has a mass of more than 500 million tons, and Little D has only about 5 million tons, which is the size of the Great Pyramid of Giza.
The DART impactor, when it finally hits Little D, has a mass of only 500 kilograms, which is equivalent to an adult male dromedary.
We can make up the picture of a camel hitting the pyramid, this sense of powerlessness...
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But we know that when speed is raised, it's a different concept. On January 15, 2009, US Airways Flight 1549 crashed into a flock of Canadian black geese just after flying together, and the two engines directly lay in their nests and had to make a forced landing on the Hudson River.
DART's head-on impact on Little D has a speed of up to 6,600 meters per second, carrying 11 billion joules of kinetic energy, which is very grand. The rotation of the small D around the big D would have taken 11 hours and 55 minutes, but after the head-on impact, the speed decreased, the orbit was lowered, and the orbital period was shortened by 32 minutes. NASA's expectation is that the experiment will be successful if it can be shortened by 73 seconds, so the impact can be called a big victory.
By the way, I will debunk the rumor in advance, because I have seen the seeds: some people understand the threshold for the success of the 73-second experiment as the design goal, and thus mistakenly interpret the actual result of 32 minutes as "the impact result is very error-free, making humans more uncertain about asteroid defense", this interpretation is wrong, this interpretation is wrong, this interpretation is wrong (important things say three times).
Our National Space Administration is also planning an active impact, which will be implemented around 2025 or 2026. Who are we targeting? What will happen to the experiment? Let's wait and see!
Source: Science Debunks Rumors