How is a potentially threatening celestial body determined? What are the circumstances under which an Earth impact notification will be received?

I have to say that the whole universe works very cleverly. Seemingly random, yet so regular. Take our Earth, for example. If the Earth had been a little further or closer to the sun, almost all living things would not have been possible. And the temperature and environment would certainly not be the same as it is now. Then there is the movement between the planets, each in its own orbit, without collision. (There is my personal summary of the article's highlights at the end of the article. If you're in a hurry, you can skip straight to the end for the summary.)

However, some asteroids and comets still have the potential to collide with planets. It is no small thing to realise that such a collision, if it happened on Earth, could cause the instant extinction of all species. For this reason, these asteroids and comets that could collide are known as potentially threatening objects.

But not all objects that collide with the Earth are a danger to the planet. Sometimes we hear about meteorites falling from the sky, but so far we haven't seen any disasters caused by meteorites on Earth. After all, meteorites are usually relatively small and the damage they usually do to the Earth is to smash a crater. The larger meteorites so far have been older. Contemporary meteorite damage is even rarer.

Since small meteorites do not pose a threat to the Earth, how big would a meteorite be to cause human panic? At least this celestial body should be no smaller than 150 metres in diameter. If an object of this size were to impact the Earth, whether on land or in the ocean, it would affect the areas where people live. The frequency of a celestial body of this size colliding with the Earth is about once in 10,000 years. For humans, this frequency is either encountered only once in a lifetime or not at all, and has not been encountered since the advent of mankind.

It is said to be imperative. It is not enough to know the size of the celestial body, but also the distance from the Earth. Only if it is close enough can it pose a threat to the Earth, otherwise this celestial body is not afraid even if it is large. Every celestial body has its own orbit. Whenever the orbit of a celestial body intersects the orbit of the Earth, one has to pay attention. It is not a sure thing that the intersection will collide. Each orbit runs at a different time, so it is possible to intersect but never collide. Just be aware of the minimum orbital intersection distance, when this is less than 0.5 astronomical units (1 astronomical unit is 150 million kilometres and 0.5 astronomical units is 72.5 million kilometres), it is classified as a potentially threatening object.

The emergence of potentially threatening objects is no small matter, but scientists are so concerned about it that they have created two indices to classify the size of potentially threatening objects. These two indices are the Palermo Technology Impact Hazard Scale and the Turin Hazard Index. They are described below, one by one.

The Palermo Technical Impact Hazard Class is a logarithmic criterion that combines two data indicators. One is the probability of impact and the other is the kinetic yield, i.e. the kinetic effect produced. So, let's start by understanding a term, background risk, which is the average number of years for another impact of the same or a larger object. And if the Palermo Technical Impact Hazard Rating is zero, it means that this NEO has the same risk as the background risk. If it is plus two, it means that the risk is one hundred times higher than the background risk (log100 is 2). If it is less than minus two, then there is nothing to worry about. If it is between minus two and zero, keep a close eye on it.

The Palermo technical shock hazard rating can be a bit complicated, but have no fear. There is also the Turin Risk Index. The Turin Hazard Index is a combination of impact probability and destructive power. Intuitively, the Turin Risk Index uses a number from one to ten and five colours - white, green, yellow, orange and red - to represent the different levels.

White means no danger. A value of zero means that it will not collide with the Earth or that it will be burned up on entry into the atmosphere.

Green means regulatory. A value of 1 means there will be little or no collision with Earth.

Yellow indicates concern. A value of 2 indicates a low probability of impact. At a value of 3, the chance of impact is slightly higher, with greater than or equal to 1% likely to cause small impact damage. If it will approach Earth within 10 years, the public and authorities should be informed. A value of 4 gives a slightly higher chance of impact, with a probability of regional damage greater than or equal to 1%. If it approaches the Earth within 10 years, the public and relevant authorities should be notified.

Orange represents the threat. With a value of 5, the chance of impact is high and a far-reaching impact would cause severe regional damage. If there is a chance of an impact on Earth within 10 years, governments could be authorised to adopt emergency response plans. A value of 6 indicates a high probability of impact and a far-reaching impact that would cause severe global damage. If there is a chance of an impact within 30 years, governments could be authorised to adopt an emergency response plan. With a value of 7, the chance of impact is very high and the threat of a very far-reaching impact would result in a global extinction catastrophe. If such a threat were to occur in the next century, international contingency plans would be authorised, in particular through the use of key observations to obtain convincing evidence as soon as possible to determine whether an impact would occur.

Red means danger. With a value of 8, a celestial impact will occur and cause damage to a local area, which happens once every 50 to several thousand years. At a value of 9, an impact will occur and cause damage to a large area, which occurs every 10,000 to 100,000 years. A value of 10 would result in a celestial collision causing global climate change and an extinction catastrophe that could destroy civilisation, occurring once every 100,000 years or more.

So far, we have not heard of potentially threatening celestial bodies in our daily lives. Is this because no one takes it seriously? No. The odds of such a thing are slim. If a celestial body is really about to collide with the Earth and the damage is not that great, then it is possible for people at the crash site to move ahead. If it would cause devastating damage to humans, if it were reported it would probably just cause panic and even lead to half-dead humans before the celestial body arrives. After all, if you know how it will end, you don't know what people will do. Maybe it's better not to know!

Personally, I think it's a summary of the main points :

1. for asteroids and comets that may collide, we call them potentially threatening objects.

2. When the diameter of the object is not less than 150m and the minimum orbital intersection distance is less than 0.5 astronomical units (one astronomical unit is 150 million km, 0.5 astronomical unit is 72.5 million km), it will be classified as a potentially threatening object.

3. Scientists have created two indices to classify the size of potentially threatening objects. The two indices are the Palermo Technical Impact Hazard Class and the Turin Hazard Index.