Asteroids are rocky , airless worlds that orbit our sun , but at the same time are too small to be called planets. Tens of thousands are concentrated in the belt main asteroid, a vast donut shaped ring between the orbits of Mars and Jupiter . Asteroids that pass close to Earth and deserve a close watch are called Near-Earth Objects or NEOs.


What is an asteroid?

An asteroid is a body in space that is smaller in size than the planets found in our solar system and that has a rocky appearance orbiting the sun in an orbit interior to that of Neptune.



The main characteristics that we can mention of asteroids are the following:

  • Until 2006, they were also known as planetoids or minor planets .
  • Some are deviated and reach orbits that cross those of the major planets.
  • Most are irregular in shape , although some are nearly spherical and often have holes or craters .
  • More than 150  are known to have a small companion moon although some have two moons.
  • There are also some  binaries or doubles , in which two rocky bodies of roughly the same size orbit each other, as well as triple asteroid systems.
  • Most of them are located between the orbits of Mars and Jupiter.
  • They are named depending on their date of discovery, usually bearing names obtained from Greek mythology .


Its discovery dates from the beginning of the 19th century , in the year 1801 , when the Italian astronomer Giuseppe Piazzi discovered the asteroid or minor planet called Ceres ; then many more were discovered. Today the existence of approximately two million asteroids is estimated.

The person in charge of giving them the name of asteroids was the English mathematician and astronomer John Herschel , who gave them that name shortly after they were spotted.


Asteroids can be subdivided into three main categories:

  • Carbonaceous (or C-type) asteroids: make up most of the known asteroids and are located in the outermost parts of the asteroid belt. They are the ones with the least amount of light since their albedo is between 0.03 and 0.09. Their chemical composition is similar to that of the Solar System and they do not have hydrogen , helium and other volatile elements.
  • Siliceous (or S-type) asteroids: they make up about 17% of asteroids and are brighter than type C. They are made up of ferrous minerals that are mixed with magnesium silicates .
  • Metallic (or M-type) asteroids: the group includes the remaining asteroids and they are located in the most central region of the asteroid belt. They are made up mainly of ferrous materials and their luminosity can be compared to that of S-type asteroids.

Some can also be classified as D-type asteroids . These have a very low albedo and their color is quite red , they are strangely found in the main belt, as they are more frequent at distances greater than 3.3 ua from the Sun.

Where they come from

The Sun and the planets were formed from a large cloud of gas , consisting mainly of hydrogen and helium to which small parts of other elements were added. This matter was concentrated in the center of this disk, originating the sun . The rest revolved around him forming a disk . Inside the disk the matter formed pieces of different sizes known as planetesimals.

The asteroids then come from the matter that was not incorporated into the planets of the Solar System and that they group in the so-called asteroid belt , between Mars and Jupiter.

Which asteroid will pass near the earth

According to NASA experts, large asteroids do not regularly approach the earth, they only do so once or twice a year. This year 2018, we have the asteroid CB , which measures between 15 and 40 meters and which will pass close to our planet, approximately 64,000 kilometers.

In addition, an asteroid of around 700 meters and that has a curious skull shape, TB-145 , will fly towards Earth in November 2018.

Which are the biggest

  • The asteroid Florence is considered the largest to have passed close to Earth. With a measurement of between four and nine meters, it approached the planet in about 17 million kilometers
  • The  AJ129 had dimensions of between 0.5 and 1.2 kilometers and, as it measures more than 140 meters and was considered a “ Potentially Dangerous Asteroid ”.
  • The  BX was about the size of a bus floating in space at 26,700 km / h.
  • The AG13 , was the size of a building with 10 floors and passed between Earth and the Moon.

Risk of asteroid impact

The constant study of asteroids that pass close to the earth has the scientific objective of controlling the possibility that some of them may collide with the planet. For this reason, their trajectories and distances are continually studied.

Some asteroids have already collided with the planet and in fact, many scientists attribute the disappearance of the dinosaurs from our earth to the collision with an asteroid. Its size is so great that a collision with our planet could cause devastating consequences for life.

Despite the fact that the possibility of a collision is very remote, it is still a reality to which we must pay attention, do not stop monitoring by studying their positions with respect to our planet.


Some curiosities of the asteroids are:

  • The asteroid that fell near Chelyabinsk , Russia, in 2013 had the same amount of energy as 30 Hiroshima atomic bombs .
  • A 10 meter wide asteroid can hit just like an atomic bomb .
  • They have an average speed of 90,000 km / hour.
  • They are made from ” leftovers ” from the planets.
  • The chances of dying from an asteroid impact are less than dying in a car accident, but higher than being struck by lightning.
  • The amount of asteroid material that hits Earth each night is about 100 tons.

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