When did asteroids appear and are they dangerous for us now?


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In the past few years, people have often discussed the possibility of a collision between the Earth and a celestial body. Xu Techs understands what asteroids are, how they appear and whether they can destroy all life

What are asteroids

Asteroids are hard, rocky bodies that orbit the Sun. In this way they repeat the behavior of the planets, but cannot be called that because of their small size. They belong to the category of “small solar system bodies.” Although there are millions of them , their total mass is less than that of the Moon.

Asteroids formed about 4.6 billion years ago, during the early formation of the solar system. Then the future planets experienced the stage of “ planetesimals ”. During this period, small cosmic particles are gradually attracted to each other, the temperature in the center increases, due to which they melt and a protoplanet is formed . Today’s asteroids are “by-products” of that process. Scientists suggest that many planetary satellites are former asteroids that were “captured” by the gravitational field of a large object, forcing them to rotate around it.

History of the discovery of asteroids

Asteroids were discovered by accident: in 1801, Italian astronomer and priest Giuseppe Piazzi discovered the largest of them and named it Ceres after the Roman goddess of fertility. It now qualifies as a dwarf planet. Since then, scientists began to regularly find asteroids: by the second half of the 19th century, the number of recorded objects exceeded 100, by 1921 – over 1 thousand, and by 1981 – over 10 thousand. Now this number exceeds 800 thousand. In 1980 , the hypothesis that it was the impact of an asteroid about 66 million years ago that led to the extinction of the dinosaurs.

According to scientists, this asteroid landed in the area of ​​modern Mexico. Most amphibians could die within a few hours or days after the fall due to a sharp increase in ambient temperature. This collision could cause irreversible climate change, increase acidity in the atmosphere and change the composition of the oceans.

Astronomer Vladimir Surdin – about whether humanity will die from a collision with an asteroid

Chemical composition and color of common asteroids

Scientists divide asteroids into classes depending on their composition. This is what the three most common ones look like :

Class C asteroids. Color: grayish. They consist of carbon and a number of other substances, including silicon. This is the most common type, comprising about 75% of all asteroids.

S class asteroids. Color: greenish or reddish. Consist of silicon, nickel and iron. The second most common type includes about 17% of all asteroids.

M class asteroids. Color: reddish. Consist of nickel and iron. Remains of metallic cores of planetesimals.

Where are the asteroids located?

Most of the solar system’s asteroids are located in the main asteroid belt, between the orbits of Mars and Jupiter. More than 200 asteroids with a diameter of more than 100 km, from 1.1 million to 1.9 million with a diameter of more than 1 km, and millions of small ones circulate in it . As scientist Vladimir Busarev writes , here they move in a “safe” zone, where the gravitational influence of large planets on them is minimal.

It was because of Jupiter that another planet could not arise in the place of the main asteroid belt during the birth of the Solar System. Its gravitational field prevented the formation of planetesimals nearby, so the particles did not connect and continued to move around the Sun in the form of asteroids.

Largest groups of asteroids

Asteroids are located in the Solar System not only in the main asteroid belt.

“Trojans” and “Greeks” , which were named after the heroes of the Iliad, are located at the “Lagrange points”. In these parts of space, the gravitational influence of the planet and the Sun is equal. Jupiter has the most “Trojans” and “Greeks” – more than 10 thousand.

Neptune has 30, Mars has nine, and Earth and Uranus have one each.

The Hilda Family contains more than 1 thousand Trojan-like asteroids. It is located beyond the main belt between the orbits of Mars and Jupiter.

The Kuiper Belt is located at the edge of the solar system, near Neptune. It is similar to the main asteroid belt, but differs in size: 20 times wider and 20–200 times more massive. It contains small bodies of water, ammonia and methane and at least four dwarf planets, to which modern science includes Pluto.

  • Location diagram of the main asteroids of the Solar system
  • Asteroids and comets: similarities and differences

A comet differs from an asteroid only in composition: star dust and ice instead of metals. When approaching the Sun, substances begin to evaporate, due to which the famous “tails” are formed.

A meteorite is an asteroid or its fragment that has reached the surface of the Earth. About 20 meteorites hit our planet every day . They are not dangerous, since in the overwhelming majority their size does not exceed a stone that can be held in the palm of your hand.

According to NASA , meteorites that can destroy a city or cause a devastating tsunami collide with the Earth every 1,000 to 10,000 years.

Large meteorites, 400 m in diameter, capable of causing a global cataclysm, hit our planet on average every 100 thousand years. Nevertheless, scientists are exploring all options to combat the potential threat.

The largest asteroids

Asteroids are difficult for researchers to measure because of their irregular shapes and varying albedo (surface reflectivity). If you count by approximate diameter, the top ten will look like this:

Ceres, 946 km
Vesta, 525 km
Pallada, 512 km
Hygiea, 431 km
Interamnia, 326 km
Europe, 315 km
David, 289 km
Sylvia, 286 km
Cybele, 273 km
Eunomia, 268 km

Asteroid research methods

In 1991, NASA’s Galileo probe sent back close-up images of main belt asteroids to Earth.
In 2001, another agency space probe, NEAR Shoemaker , successfully soft- landed on the asteroid Eros for the first time in history . After working there for two weeks, he stopped communicating.

In 2006, the Japanese spacecraft Hayabusa (translated as “Falcon”) landed, took samples, and then took off from the Itokawa asteroid. In 2010, he returned to Earth.

In 2019, Hayabusa2 successfully landed on the distant asteroid Ryugu, which is located 280 million km from Earth. In 2020, a capsule with soil samples collected by the probe arrived on Earth.

In October 2021, NASA sent the Lucy mission , which will study the Trojans for more than 10 years.

“An asteroid is approaching Earth! What to do?”

In 1998, American congressmen asked NASA to record all asteroids and comets with a radius of 1 km or more that could be in Earth’s orbit. Since then, NASA astronomers have discovered 95% of asteroids, and some of them could hypothetically lead to the end of the world. Currently, none of them threaten our planet.

Nevertheless, the US Congress raised the bar back in 2005, ordering NASA specialists to find all asteroids with a radius of 140 m. They are also called “ city killers ”, as they are capable of wiping a metropolis off the face of the Earth. The probability of encountering them in any age is about 1%. Now NASA has found about 40% of them. It will take about another 30 years to discover the remaining 60%.


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