What will happen if a very large celestial body hits the earth?

Asteroids that may collide with the earth in the future and exceed a certain size are called potential threat asteroids (PHA).

Specifically, all asteroids that are less than 0.05 astronomical unit (about 8 million kilometers) from the Earth and have a diameter of more than 100 meters (330 to 490 feet) are considered as potential threat asteroids.

Up to 20 16 1, astronomers have discovered about 165 1 asteroids with potential threats, which may bring danger or other influences to the earth.

It is believed that 153 is more than one kilometer in diameter.

The figure below shows the cumulative number of asteroids with potential threats detected since 1999. It can be seen that the speed of discovering new asteroids with potential threats has dropped significantly.

This means that we have found almost all of them now.

Even so, if one of the few undiscovered guys hits the earth, it will be a terrible disaster, so it is necessary for us to 100% find them.

By the way, the chart data comes from Wikipedia's "Potential Threatening Asteroids" page.

The asteroid with the greatest potential threat is (533 19) 1999 JM8, with a diameter of about 7 kilometers, but it does not bring any impact risk at present.

Ida, an asteroid located in the asteroid belt outside the orbit of Mars, is shown in the following figure. Its volume is 60km x 25km x 18km, which can give you a general idea of what these boulders look like.

The smaller the asteroids, the more they are, which is the general rule of thumb of the solar system.

According to the most accurate estimate, an object with a diameter of three meters hits the earth every year, releasing energy equivalent to 2000 tons of TNT.

Every few hundred years, an object with a diameter of about 100 meter will hit the earth, releasing energy equivalent to 200 megatons of TNT.

About every/kloc-0.0 million years, an object with a diameter of kilometers will hit the earth, releasing energy equivalent to/kloc-0.0 trillion tons of TNT.

The good news now is that the earth's atmosphere can protect us from objects that were originally below about 100 meters, because they will evaporate and decompose when they reach the ground. However, in 1908, the famous Tunguska event was that a stone meteor with a diameter of 50 meters burned out about 20 kilometers above the earth's surface, and all the trees within 30 kilometers were squashed. Its power is equivalent to about 10 megaton TNT, and the frequency distribution table predicts that such an impact will occur every 100. We are lucky to meet again on 20 13!

13, 15 February, a once-in-a-century event happened. An asteroid with a diameter of 20 meters was suddenly born in Chelyabinsk, Russia, with an explosion energy of 500,000 tons, which is about 30 times the explosion power of Hiroshima atomic bomb. The following photo was taken by the dashboard camera to record this event. More than 1500 people were injured or even hospitalized because of broken glass in flight. This incident also happened in new york, where more than 6,543,800 people were injured and hospitalized, and the windows of skyscrapers were broken and fell into the streets.

The impact of the ocean on this object will spread about 300 meters, and the tsunami tide will bring more damage than the comparable impact on land. The Tunguska incident occurred in a densely populated city, and its damage was equivalent to an earthquake of magnitude 7.0 or above, which caused thousands of people to die because they were buried under the ruins of improperly designed buildings or in the fire caused by the impact. Fortunately, human beings only live in a small part of the earth's surface. Even if these impacts happen, they only happen once a century, so no one can see them approaching in the past.

Ocean impacts within 700 meters will generate huge tides and reach the coasts of many continents. Within the range of 1-2 km, these tsunamis will reach 300 feet high and extend inland for 20 km or more, thus putting 1 10,000 people or 10% of the world population at risk. This kind of impact will be directly detected by NORAD several days in advance, so the question is whether enough people can be safe. Of course, when they return to their coastal cities or homes, most of them will suffer serious disasters or be washed away by huge tides!

I didn't even mention the huge asteroid impact that happens every few million years or so. This will be enough damage caused by more frequent "Super Tunguska" events, which can make our life more fulfilling and busy!