The concept of planet comes from the Latin planitata , which, in turn, derives from a Greek term meaning “wanderer.” It is a solid celestial body that rotates around a star and becomes visible due to the light it reflects.
General characteristics
Today, the Solar System is considered to be made up of eight planets: Mercury, Venus, Earth, Mars, Saturn, Uranus and Neptune. Until 2006, Pluto was considered a planet, but then it was classified as a dwarf planet.
Structure
According to their structure, planets can be classified as Jovian and telluric or terrestrial. The former have low density, are gaseous and have a large diameter (like Jupiter for example). The others, on the other hand, are solid and rocky and have high density (like Mars and Earth).
Motion
Regarding their movements, the planets can be internal or external: the internal ones correspond to those planets that are not so far from the Sun and that are not in opposition and the external ones can be in opposition and their angles of elongation are unlimited. .
The main planets of the Solar System
The Solar System is made up of eight main planets:
- Mercury
- Venus
- Land
- Mars
- Saturn
- Uranus
- Neptune
Characteristics of each planet
Mercury
Mercury is the innermost planet in the Solar System. It is so close to the Sun that, if seen by an astronaut visiting the planet, it would appear two and a half times larger and seven times more luminous than when seen from Earth.
Mercury’s motion is characterized by a particular relationship between its axis and the orbital period around the Sun: the rotation period, equal to 58.65 Earth days, lasts exactly two-thirds of the orbital period (its “year”) which is equal to 87.95 days.
Structures that were not seen on the Moon were observed on Mercury, including a system of large fractures in the crust, generally interpreted as indications that the planet underwent a contraction process, probably due to the effect of the gradual cooling that took place after of his training.
Venus
In the past Venus suffered intense volcanic activity and it is thought that there may still be expulsion of gases and lava. Venus, the second planet in the solar system, closest to Earth and the brightest star in our sky, after the Sun and the Moon.
The orbit that the planet travels in 225 days is practically circular. The rotation on its axis is extremely slow, with a “day” lasting almost 243 Earth days, taking place in the opposite direction, unlike the other rocky planets in the Solar System.
The surface of this planet is a true hell, with an atmospheric pressure 90 times higher than that of Earth and a temperature of 500 ºC, due to the greenhouse effect. Its atmosphere is made up almost entirely of carbon dioxide (CO2), with a little nitrogen (nitrogen).
Land
The Earth is the third planet in the solar system, from the Sun and the fifth in diameter.
It takes approximately 365 days to make a complete revolution around the sun (translational movement) and 24 hours to make one revolution around itself (rotation movement).
It has a natural satellite which is the Moon.
Among the planets in the Solar System, Earth has unique conditions: it contains large amounts of water, has tectonic plates and a strong magnetic field. The atmosphere interacts with living systems.
Modern science places Earth as the only planetary body that has life.
Mars
Known for its characteristic reddish color, the planet orbits the Sun at an average distance of 228 million kilometers.
Being the most distant of the rocky planets, it is a small, arid planet whose internal structure is not yet known of what it is composed of. However, through the average density, the polar flattening and the rotation speed, it is possible to deduce that the planet has a core of iron and iron sulfate with about 1,700 km in radius, and a crust with around 200 km thick, markedly elliptical, taking 686.98 days to make a complete revolution around the Sun and its orbital plane has an inclination of just 1.86º with respect to the Earth’s orbit.
It is accompanied in its movement by two small satellites (Deimos and Phobos) discovered in 1877.
Jupiter
It is the largest planet in the solar system, it has 63 satellites. Its name comes from the king of the gods of the Greco-Roman tradition, located at an average distance from the Sun of 778.33 million kilometers, it takes 11.86 years to describe a complete (slightly elliptical) orbit.
What is most impressive about this planet is its gigantic dimensions. With a radius of 71,492 km, a volume 1,300 times greater than that of the Earth and a mass equivalent to almost 318 Earth masses, Jupiter surpasses all other bodies in the Solar System, except the Sun.
The most spectacular formation in Jupiter’s atmosphere is the so-called Great Red Spot, an atmospheric disturbance, more than 30,000 kilometers long, that has lasted for 300 years.
Saturn
Until 1977, it was best known for being the only planet surrounded by a ring system. From then on, thanks to advanced observations made from Earth and the fascinating discoveries of the Voyager probes, Saturn became a major attraction.
After Jupiter, Saturn is the second largest, with a mass and volume 95 and 844 times, respectively, those of Earth. From these data it is deduced that it has an average density equivalent to 69% of that of water, which indicates that light elements, such as hydrogen and helium, predominate in the composition of this celestial body.
Several cyclone-like formations, brown or light in color, are also observed on Saturn, although none comparable to Jupiter’s Great Red Spot. These are rings of around 1,200 km, short in duration and present only in high latitudes.
Uranus
It is the first planet discovered in modern times, it is only visible under especially favorable conditions. Located at an average distance from the Sun of 2,871 million kilometers, it takes 84.01 years to describe a complete revolution around the Sun.
It is a singular planet, whose axis of rotation practically coincides with the orbital plane. With an equatorial radius of 25,559 km and a mass equivalent to 14.5 Earth masses, the planet Uranus can be considered the twin brother of the distant Neptune.
The blue-green color of the atmosphere is due to the abundance of gaseous methane (2% of molecules) that absorbs sunlight. Furthermore, the compound condenses at fairly high altitudes and forms a cloud layer.
Neptune
Neptune’s orbit is located at a distance of 4,497 million kilometers from the Sun and it takes 165 years to complete one revolution. Thus, since it was discovered (in September 1846) it has not yet made a complete revolution around the Sun. The planet has a mass 17 times greater than that of the Earth, and an average density equal to 1.64 times that of water.
Like all gas giants, it does not have a clear separation between a gaseous atmosphere and a solid surface.
Its atmosphere is basically made up of hydrogen and helium, with a small percentage of methane. This last compound, which absorbs red light from the Sun, gives it a characteristic coloration that influences the meteorology and chemistry of the planet.