asteroid

Astronoma

2022

We explain what asteroids are, where they come from, their classification and characteristics. Also, differences with comets.

Asteroids look like stars but don't really have their own light.

What is an asteroid?

An asteroid is a type of space rock, much smaller than an planet, and travels in an elliptical orbit around the Sun. There are millions of asteroids and most of them are in the so-called "asteroid belt”. The rest is distributed in the orbital trajectory of other planets of the Solar system, among them, the Earth.

Asteroids are the subject of constant study due to the closeness they maintain with the Earth. The odds impact is very low despite the fact that in a very remote past they have reached our planet. In fact, many scientists attribute the disappearance of the dinosaurs to the impact of an asteroid.

Name asteroid comes from the Greek meaning "stellar figure" and refers to their appearance since, when observed with a telescope from Earth, they seem stars. For much of the 19th century, asteroids were called "planetoids" or "dwarf planets."

Where do asteroids come from?

The hypothesis argues that asteroids are remnants of the cloud of gas and dust that condensed about five million years ago, when the Sun and Earth formed. Part of the matter Derived from that cloud, it gathered in the center and formed a nucleus that gave rise to the Sun.

The rest of the matter, which revolved around the new nucleus, formed pieces of different sizes called "planetesimals". The asteroids come from part of that matter that was not incorporated neither to the Sun nor to the planets of the Solar System.

Types of asteroids

Asteroids are classified into three groups, according to their location and their type of grouping:

  • The asteroids of the Asteroid belt. They are those that orbit in space or border, between Mars Y Jupiter. The belt conglomerates most of the asteroids in the Solar System.
  • Asteroids Centaurs. They are what orbit at the border between Jupiter or Saturn, and between Uranus or Neptune, respectively.
  • Trojan asteroids. They are the ones who share the orbit of a planet, but they do not usually impact.

The asteroids that are closest to our planet are subdivided into three types:

  • Love asteroids. Those that cross the orbit of Mars.
  • Apollo asteroids. Those who cross the orbit of the Earth and therefore are a relative threat (despite the low risk impact).
  • The Aton asteroids. Those that partially cross the Earth's orbit.

Asteroid characteristics

Asteroids are characterized by having a Gravitational force very weak, which does not allow them to reach a completely sphere shape. Its diameter can vary from a few meters to hundreds of kilometers.

They are composed of metals and rocks (clay, silicate rocks and nickel-iron) whose proportions may vary according to each type of star light blue. They do not have atmosphere and some have at least one satelite.

From the land surface, asteroids look like tiny dots of light, as if they were stars. Due to their small size and their great distance from Earth, what is known about them was obtained based on astrometric and radiometric measurements, light curves and absorption spectra (astronomical calculations that allow us to know a large part of our Solar System).

Asteroids and comets

Comets are known for their wake.

Asteroids and comets have in common that they are celestial bodies that orbit the Sun, that tend to make unusual paths (such as approaching the Sun or other planets) and that they are remnants of the matter that gave rise to the Solar System.

However, they differ in that comets are composed of dust and gases and, in addition, of particles of ice. Comets are known for the tail or wake they leave behind, although they don't always leave a trail.

Containing ice, its state and appearance vary depending on the distance from the Sun: they are very cold and dark when they are far away, or they become hot and expel dust and gas (hence the origin of the tail trail) when they approach the Sun Comets are believed to have deposited Water and other organic compounds on planet Earth when it was just forming.

There are two types of kites:

  • Short-lived. Those comets that take less than two hundred years to complete an orbit around the Sun.
  • Long-term. Those comets that make long and unpredictable orbits. It can take up to thirty million years to complete one revolution around the Sun.

Asteroid belt

The asteroid belt lies between the orbits of Mars and Jupiter.

The asteroid belt consists of the union or the approximation of several celestial bodies distributed in the form of a ring (or belt), located between the border of Mars and that of Jupiter.

It is estimated that it has about two hundred large asteroids (with a diameter of 100 kilometers) and almost a million small asteroids (which have a diameter of one kilometer). Due to the size of the asteroids, there are four that were identified and that stand out:

  • Ceres. It is the largest in the belt and the only one that came very close to being considered a planet due to its fairly well-defined sphere shape.
  • Vesta. It is the second largest asteroid in the belt, the one that contains the largest mass and the oldest density. Its shape is flattened spheroid.
  • Pallas. It is the third largest in the belt and its orbit is slightly inclined, something particular for a body of its size.
  • Hygieia. It is the fourth largest in the belt, with a diameter of four hundred kilometers. Its surface is very dark, which makes it difficult to identify it.
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