Threats from space: will humanity die from a collision with an asteroid

We tell you why outer space is dangerous and after how many years humanity can die from an asteroid collision with the Earth

At the end of the Cretaceous period, a meteorite fell to Earth, destroying the dinosaurs. More than 66 million years have passed, but the cosmos is still unpredictable, even though humans have made great strides in terms of innovation and have almost made space travel possible for everyone.

However, the situation with a meteorite that fell many years ago may repeat itself. About 20 meteorite craters have survived on the surface of the Earth, similar in scale to those that destroyed the dinosaurs. It is impossible to calculate exactly on what day a space object will fall to Earth. But the frequency of meteorites falling, like the one that killed the dinosaurs, is already known – 100 million years. If the last one fell 64 million years ago, then formally humanity still has about 40 million years left, but this does not mean at all that this will happen in reality. Vladimir Surdin – astronomer, senior researcher at the State Astronomical Institute named after P.K. Sternberg, Associate Professor of Moscow State University, told how scientists are trying to prevent the collision of space objects with the Earth and which of them can fly to our planet in the near future.

Collision with the Earth: how scientists determine the level of danger of asteroids

The collision of the Earth with dangerous space objects does not occur when they move along the same trajectory, but at different times. Now space researchers note the four most dangerous asteroids, the trajectories of which intersect with the Earth:

• 1950 DA (one Earth impact possible);
• Bennu (1999 RQ36) (78 collisions possible);
• Apophis (2004 MN4) (possibly 12 collisions);
• 200 SG344 (101 collisions possible).

Astronomers rank asteroids on the Palermo scale, a special scale of danger. Until 2021, Apophis (2004 MN4) was considered the most dangerous, with a diameter of about 325 m. Its average approach to the Earth is about 31 thousand km from the planet’s surface (about 1/10 of the distance from the Earth to the Moon). Scientists managed to find out that in the next 100 years the asteroid is not dangerous – it will most likely fly by.

Dangerous space objects: from asteroids to interstellar objects

Asteroids are not the most dangerous space objects. They can be counted, and since they move in a limited region of the solar system (in the main asteroid belt, between the orbits of Mars and Jupiter) in almost circular orbits, they are also easy to observe. To date, more than 1 million asteroids have been discovered: all of them are larger than a kilometer in diameter. Telescopes of the new generation with a wide field of view make it possible to follow these space objects.

Comets are more dangerous and unpredictable. They come from the most distant regions of the solar system, where the sun’s rays no longer penetrate, so it is impossible to notice comets. They move around the Sun in an elongated orbit, and as they approach it, it develops a tail millions of kilometers long. At the moment when the comet is noticed, two or three years will have passed since it flew past the Earth: it is impossible to secure its movement for the surface of the planet in such a short period of time. The comet turned out to be the well-known Tunguska meteorite, which collided with the surface of our planet in the area of ​​the Podkamennaya Tunguska River in 1908. The Tunguska meteorite knocked down trees in an area equal to that of Moscow.

The most dangerous space object is interstellar. It is not bound by gravity to any star. For the first time, an interstellar object was discovered in 2017: a body from another (unknown to us) planetary system was noticed in space near the Sun. It swept close to Earth at great speed and was named 1l/Oumuamua (C/2017 U1), which in Haitian means “the first herald from afar.” The shape of the interstellar object resembles a huge elongated cigar. Some have speculated that the interstellar object could even be an alien ship.

Another object that was potentially dangerous, as it unexpectedly flew close to the Earth, is the comet Borisov (Borisov), discovered using a homemade telescope by Gennady Borisov, an engineer at the Crimean Laboratory of the State Astronomical Institute named after P.K. Sternberg Moscow State University. It is the first known interstellar comet.

Other space objects are meteors and meteorites. Meteors flicker and burn up in the earth’s atmosphere. Meteorites fall to the surface of the Earth.

How to prevent an asteroid from colliding with the Earth: spraying dangerous objects and the Yarkovsky effect

The first thing humanity needs to do is build telescopes and observatories. A large telescope can see a space object long before it approaches Earth’s orbit. The ground-based telescope must be equipped with a very large segment of mirrors with a diameter of 39,3 m.

There are several ways to repel an asteroid attack, but astronomers alone cannot cope with it – they need to mobilize forces to create a powerful technological invention: for example, a laser gun or a rocket gun that would be loaded with nuclear bombs that turn a space object into dust.

So far, calculations show that the current combat arsenal of earthlings is not able to prevent a collision of a large asteroid with the planet. Space objects with a diameter of less than a kilometer (500–900 m) could be sprayed. Up to 5 km – break into separate parts, however, even these pieces will fall and cause considerable damage. In any case, scientists are not going to destroy asteroids, they want to gently “turn” them away from the Earth using a rocket to attack asteroids (like SpaceX Starship) or sunlight reflectors (Solar Sails) – this can change the trajectory of space objects. To do this, you need to anticipate in advance when they will fly close to the Earth.

Unfortunately, observing outer space through a telescope, it is impossible to determine exactly where the target is: through a thick layer of air, it looks like a blurry shining spot. One way to prevent an asteroid from colliding with the Earth is to mark the space object with a marker (for example, a radio beacon) that will allow you to notice it and track its movement. Radio astronomers point their telescopes much more accurately than optical astronomers.

Several thousand asteroids are known, which means that it is necessary to launch several thousand rockets that will fly up to them, fixing radio beacons. They already did that a few years ago. In 2014, the Japanese Space Agency launched the Hayabusa-2 spacecraft to orbit the Ryugu asteroid, and two years later, the United States launched the OSIRIS-Rex automatic interplanetary station to the Bennu (1999 RQ36) orbit, which landed on the asteroid in 2019.

Bennu is potentially one of the most dangerous space objects. Its diameter is 560 m. For comparison, the height of the Empire State Building is 443 m, and the Eiffel Tower is 324 m. Presumably, Bennu will approach the Earth in 2175-2199, but its trajectory can still be changed using nuclear charges. The probability of an asteroid colliding with the Earth earlier, in 2023, is 0,04%.

The sun’s rays are one of the options for influencing the asteroid. Of course, they have little effect on space objects, but even such a force over many years can gradually divert the asteroid from a dangerous trajectory. The strongest effect of the sun’s rays was discovered in 1900 by the Moscow engineer and naturalist Ivan Yarovsky. He found that thermal radiation gives the astroid an additional acceleration force. Imagine: sunlight warms the daytime surface of the Earth, but the warmest state of the Earth’s surface is in the evening. Cooling down, the planet gives off infrared radiation into space, which works like a jet engine (in science fiction novels it is called a photon rocket). The Yarkovsky effect affects bodies up to ten meters in diameter. It turns out that if a dark-colored asteroid is sprinkled with chalk, which reflects the rays and does not allow its surface to heat up, it is possible to increase the absorption of sunlight and weaken the Yarkovsky effect. If sprinkled with coal dust, the asteroid will absorb sunlight – the pressure will decrease, but the Yarkovsky effect will increase.