Before humans appeared, dinosaurs ruled the earth for hundreds of millions of years. But about 66 million years ago, an asteroid with a diameter of about 10 kilometers fell on Gulf of Mexico at a speed of 20 kilometers per second. The violent impact instantly created a huge pit with a diameter of about 100 kilometers and a depth of about 30 kilometers. As many as 25 trillion tons of rocks were thrown into space. As these rocks fell back to the ground, they rubbed and burned in the atmosphere, turning into fireballs, igniting forests all over the world. The earth was wrapped in dust, the sun could not shine in, and the temperature dropped sharply. 75% of animals and plants became extinct, and dinosaurs died of starvation, leaving only a few that became today's birds and chickens.
asteroids hit the earth and extinct dinosaurs
Our solar system is not only 8 large planets and their satellite . There are also hundreds of millions of large and small stones and "gravel piles" in the vast space. Astronomical words call them "asteroids".
Like the earth, asteroids also orbit the sun. Occasionally, they will change their orbits due to the disturbance of the planet's gravity. Some will intersect with the orbits of the earth, and even turn into meteors and hit the ground.
There are many asteroids around the earth
The atmosphere of the earth is very dense, and most meteors will heat up, burn violently during friction with the air, and eventually turn into ashes. But when a meteor is relatively large, such as a diameter of 20 meters, or is composed of iron that is not easy to disintegrate, it will cause great damage to the ground.
So far, scientists have discovered more than 29,000 potentially threatening NEO bodies, all of which are more than 140 meters in diameter, of which 878 are larger than 1 kilometer in diameter. These celestial bodies are closely monitored because once they fall, they can cause a catastrophe to a city, a country, and even most living things on the planet.
Near-Earth celestial bodies always threaten our survival
Unlike dinosaurs, humans will not sit and wait for death. Scientists can not only observe asteroids, but also accurately calculate the orbits of these uninvited guests, the time they approach the earth, and judge the possibility of their impact on the earth.
When we realize that an asteroid may cause great damage to the earth in the future, we will find ways to destroy it or deflect it orbit. This is called the Planetary Defense Project.
We also have the "Planetary Defense Plan"
There has always been controversy in the scientific community about the method of "save the earth". Some people suggest launching missiles at the asteroid and using nuclear warhead to break it up. Even if it is not broken, it can change its flight orbit; some people think that the asteroid can be equipped with an engine and push it away with long-lasting thrust; some people say that neither bombing nor pushing can solve the problem, and it is the most convenient to impact. What is the best way to use
?
Some near-Earth celestial bodies look like a diameter of several hundred meters. In fact, they are "gravel piles" composed of many large and small stones and dust. The pressure inside it is not enough to make it dense, and the heat energy generated by the decay of radioactive element is lost very quickly and cannot melt into a whole like a planet. If we detonate a nuclear bomb on its surface, most of the energy of the explosion will be absorbed and weakened by the gravel pile. Then, under the action of universal gravity, the scattered stones will gather together again and turn into an asteroid with nuclear radiation .
nuclear bombs destroy asteroids is not reliable
Install asteroids with a rocket jet engine and push it away like a "walking earth". This idea sounds good. However, most small celestial bodies also have spins while operating. Its shape is irregular and its surface is uneven. It is difficult to ensure that the rocket engine always jets in the direction we want. Therefore, it is very difficult to push the celestial bodies out of the earth's orbit by "slow push".
996, American astronomers observed a near-Earth object with a diameter of 0.8 kilometers (65803). In 2003, the observatory of the Czech Academy of Sciences discovered that 65803 actually had a "satellite". Since the average diameter of this satellite reached 170 meters, scientists named the binary system "Didymos", which is "twins" in Greek, and the "brother" is called "Dimovs" Dimorphos.
"dart" hit the asteroid "twins"
"twin brother" rotates around the "brother". Its revolution period is about 11 hours and 55 minutes. So NASA scientists wanted to launch a spacecraft to impact it. By observing the changes in the revolution period of "Dimovs", they can judge the effect of the impact, but the impact will hardly affect the "twin brother".
NASA's spacecraft is called "Double Asteroid Redirection Test" (English abbreviation DART, "Dart"), with a total investment of US$313 million. In fact, the main part of the "dart" is a 610-kilogram impactor, which has no other scientific equipment except the navigation system, communication system, propulsion system and a camera. After calculation, scientists believe that if the "dart" collides in the direction of the "Dimovs", its orbital cycle can be accelerated by 10 minutes, and vice versa, it will be slowed by 10 minutes.
Compared with asteroids, DART is insignificant
"Dimovs" mass is about 5 billion kilograms, which is about the same size as a stadium; the mass of the "dart" impactor before the collision is only 500 kilograms, 1.8 meters square, and using it to hit the asteroid is a bit like a shaking tree.
However, as long as the impactor flies fast enough, its kinetic energy will be very high. When this kinetic energy is transmitted to the asteroid, it can still slightly change the flight speed of the asteroid. NASA actually doesn't need to spend money, and you can know what the result of a collision can produce through calculations.
Knowing the result, knowing that the impact will not change the flight trajectory of the asteroid "65803", why do you still spend a lot of money to do it?
Because the result of orbital calculation is science, aiming at the target to implement collision is technology, and combining science and technology is productivity, and it is the embodiment of a country's scientific and technological strength.
"Dart" accurately hits the target
"Dart" took a total of 10 months from launch to impact. The impact location is about 11 million kilometers away from the earth. In fact, the spacecraft's flight distance is far beyond this. The entire process of "dart" from launch to flight is accompanied by precise telemetry technology, orbital calculation and flight control. If there is a slight mistake in any link, the "dart" will not hit the target.
"Dart" (pink) and asteroid (green) flight trajectory
Considering the delay in long-distance signal transmission, "Dart" needs to fly completely autonomously in the last 4 hours of flight. Also, because the start of the orbital control engine will cause the long sun wing to vibrate, which will cause the camera image to blur. Therefore, the engine cannot be turned on for orbital corrections a few minutes before the collision. There is only one chance, and the spacecraft needs to aim very accurately to hit the bull's eye.
So can NASA's "dart" impact technology really save humanity in the future?
Theoretically, as long as we discover near-Earth celestial bodies early enough, even if there is a slight change in the target's speed or flight angle, it will be enough to affect its movement trajectory and eventually pass by the earth. From this perspective, any attempt by human beings is of great significance and is worthy of recognition.
References and pictures source:
SPACE.com: "nasa dart asteroid impact planetary defense success"
Wikipedia: Chikthulub crater, near-Earth celestial body, (65803) Didymos, Dimorphos, Double Asteroid Redirection Test
#American spacecraft successfully hits asteroid#
