- What are the planets of the solar system?
- formation of the solar system
- Characteristics of the planets of the solar system
- solar system planets
- Is Pluto a planet?
We explain what the planets of the solar system are, their individual and general characteristics. Also, how the solar system was formed.
What are the planets of the solar system?
The Solar system or planetary system is the set of astronomical objects gravitationally linked to each other, of which the planet Earth, along with seven other known planets: Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune.
Broadly speaking, the planets They are large spherical masses of matter compact orbiting the Sun in regular periods, some of them composed of solid elements, others by gaseous accumulations. the immense force of gravity of the Sun is what keeps them in their orbits respective, whose location allows them to be classified into two subsets: the inner planets and the outer planets.
- The inner planets. This first group is made up of Mercury, Venus, Earth and Mars, distributed between the Sun and the Sun. asteroid belt after Mars. They are smaller planets with a solid surface, which move in shorter and faster orbits. Of these, only Mars and Earth have satellites own.
- The outer planets. This second group is made up of Jupiter, Saturn, Uranus and Neptune, distributed between the asteroid belt and the Kuiper belt, in the farthest portion of the solar system. They are planets of larger size and gaseous constitution (they are often known as "gas giants"), of which it is not yet known whether or not they have a surface.
Just as the planets orbit around the Sun, other small celestial bodies, known as natural satellites, orbit around some planets, trapped in their gravitational field. In some cases these satellites are tiny and very numerous, as is the case with Saturn, while in other cases they are larger and have their own names, such as the moons of Mars: Deimos and Phobos.
In addition to the planets and their respective satellites, the solar system is made up of other astronomical objects, among which the following stand out:
- The Sun. It is the central star of the system and the brightest object in the terrestrial sky. It occupies 99.86% of the mass of the solar system and is a star type-G that crosses its main sequence, with a diameter of 149,597,870.7 km.
- The dwarf planets. In addition to the eight known planets, there are five dwarf planets, with similar properties but much smaller in size and low in orbital dominance (that is, they can share their orbits with other objects).
- minor bodies. This is the name given to conglomerates of astronomical objects of various sizes and shapes, which are neither planets nor satellites, and do not always have stable and predictable orbits. These objects are grouped in the asteroid belt that separates the inner solar system from the outer one, as well as in the Kuiper Belt that is beyond the orbit of the last planet, or the Oort cloud that is even further away, almost one light year from the Sun.
Finally, it is important to understand that the solar system is not a static place, but in turn moves within a larger system that is the galaxy, and that in our case we have baptized as the Milky Way. Within this galaxy, our solar system is in a peripheral region, at the end of one of its spirals.
formation of the solar system
According to scientific estimates, the solar system formed about 4.6 billion years ago, following the gravitational collapse of a large molecular cloud.Most of the matter accumulated in the center and gave rise to the Sun, while the rest of it flattened to form a protoplanetary disk, that is, a disk of matter around a young star, from which a lot of stars emerged. then the planets and asteroids.
This explanation responds to the theory proposed in the eighteenth century by Emmanuel Swedenborg (1688-1772), Immanuel Kant (1724-1804) and Pierre-Simon Laplace (1749-1827), although in later centuries (especially in the twentieth century, with the beginning of space exploration) was refined and redefined to incorporate the most recent discoveries and observations in space.
Since its initial moments, the solar system has evolved and been transformed intensely, as a result of the expulsion of materials from the Sun, and also from the numerous collisions that occurred between objects born from the planetary protodisk, or also from outside the system. solar. But the gradual cooling (especially of the inner solar system) was necessary for the unions of molecules very volatile and could form rocky planets, like ours.
Characteristics of the planets of the solar system
The planets that make up the solar system are of two types: eight law planets and five dwarf planets. The difference between one and the other has to do, according to the International Astronomical Association, with three main features:
- A planet must orbit the Sun (and not other astronomical objects in the solar system);
- A planet must have dough enough to reach hydrostatic equilibrium and acquire a relatively spherical shape;
- A planet must exercise orbital dominance, that is, it must not share its orbit with other planets. celestial bodies.
Therefore, the planets of the solar system are eight (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune) and the dwarf planets are five (Pluto, Ceres, Eris, Haumea and Makemake).
The planets, however, are masses in constant movement, which complete their journey around the Sun (that is, their movement of translation) at different times: the farther they are from the Sun, the slower and longer their orbit will be. In addition, the planets rotate on their own axis (that is, a movement of rotation) at a different rate and in a uniform direction (except for Venus and Uranus, which spin "upside down"). The axis and speed of rotation of each planet is different and depends in principle on its composition.
A comparison of the properties and characteristics of known planets yields data such as the following:
| Planet | Diameter at the equator (km) | Distance to the Sun (km) | number of satellites | Time to rotate | Time to give a translation |
| Mercury | 4,879.4km | 57,910,000km | 0 | 58.6 days | 87.97 days |
| Venus | 12,104km | 108,200,000km | 0 | 243 days | 224.7 days |
| The earth | 12,742km | 149,600,000km | 1 | 23.93 hours | 365.2 days |
| Mars | 6,779km | 227,940,000km | 2 | 24.62 hours | 686.98 days |
| Jupiter | 139,820km | 778,330,000km | 79 | 9.84 hours | 11.86 years |
| Saturn | 116,460km | 1,429,400,000km | 82 | 10:23 a.m. | 29.46 years |
| Uranus | 50,724km | 2,870,990,000km | 27 | 17.9 hours | 84.01 years |
| Neptune | 49,244km | 4,504,300,000km | 14 | 4:11 p.m. | 164.8 years |
solar system planets
1. Mercury
Astronomically and astrologically represented by the symbol ☿, Mercury is the closest planet to the Sun and the smallest of all the inner planets. Devoid of natural satellites, it is a rocky planet, made up of 70% metallic elements (iron, in particular) and the remaining 30% are various silicates, making it the second most dense of the entire solar system, after the Earth.
Mercury has a dry surface riddled with impact craters. meteorites and other astronomical objects, many of which are close to 4 billion years old, as the planet has virtually no atmosphere to slow these objects down. Being so close to the Sun, Mercury's surface is hot during the day, hovering around 350°C; but at the same time the absence of an atmosphere gives it freezing nights of around -170° C.
The first observations of Mercury date from the earliest antiquity (3rd millennium BC), but its current name refers to the Roman god Mercury, a variant of the Greek god Hermes. The latter was the name that the Greeks gave him when they observed him during the evening, while in the morning sky they called him Apollo. The first to realize that it was the same star was the philosopher and mathematician Pythagoras of Samos (c. 569 – c.475 BC).
2. Venus
Represented with the ♀ sign in the astronomy Y astrology, Venus is an inner planet that lacks satellites and is the second brightest object at night on Earth (after the Moon). Its name pays homage to the Roman goddess of passionate love, the same one that the Greeks called Aphrodite.
Like the other inner planets, Venus is a rocky planet, but it is enveloped in a thick atmosphere of carbon dioxide (CO2), molecular nitrogen (N2), and hydrogen sulfide (H2S), which are known greenhouse gases. greenhouse effect. For that reason, Venus is the hottest planet in the solar system, much hotter than Mercury, despite the latter being closer to the Sun. temperature average is 463.85 °C.
This atmosphere also gives Venus a yellowish-white color, and a atmospheric pressure 90 times larger than Earth.On the other hand, its rotational movement is particularly slow (and contrary to that of most of the planets), so that on Venus a day lasts considerably longer than a year. In general, it is a place incompatible with life, although there is evidence of certain organic compounds on its surface that could suggest the presence of bacteria.
3. The Earth
Earth, our planet, is quite unique compared to the rest of the solar system. Not only because we are in it, the only ones living beings self-aware that we know of, but because it is the only planet that has liquid water and a biosphere flourishing for several billion years. There are many theories and explanations for this phenomenon, but the truth is that the planet is at the ideal distance from the Sun, which means that it is neither too hot nor too cold.
It is the densest planet in the entire solar system, and the fifth largest in proportions. The Earth has a core of iron and nickel whose internal movements generate a powerful magnetosphere, and at the same time a atmosphere not too dense, composed of 78% nitrogen, 21% oxygen and the rest are other substances such as argon, carbon dioxide, ozone and water steam. Thanks to the heat retention of the atmosphere, the planet has a climate benign and stable, otherwise its average temperatures would be around -18 °C.
71% of the earth's surface is covered by water, particularly salt water from the oceans, and the hydrological cycle it is what keeps the atmosphere fresh and stable, in addition to the exchange of elements that led to the emergence of life. Earth has only one natural satellite, the Moon, whose origin is estimated to be a dwarf planet or planetoid that shared an orbit with the planet and ended up crashing with it approximately 4.53 billion years ago.
The name of the Earth comes from the Roman word Terra, equivalent to the Greek Gaia, a primeval goddess associated with fertility and femininity, equivalent to Mother Earth in other mythologies and religions. In astronomy and astrology the planet is represented by the symbol ♁.
4. Mars
Mars is the last of the inner planets, named after the Roman god of war, equivalent to Ares of the Greeks, and also known as the "red planet" because of the abundant iron oxide on its surface. It has two small, irregularly shaped natural satellites called Phobos (from the Greek phobos, “fear”) and Deimos (from the Greek let's say, "terror"), whose origin is unknown but which could be asteroids captured by the gravity of the planet.
It is a smaller planet than Earth, but it shares many physical characteristics with it, as well as a similar rotation period and orbital cycles. Mars has a light atmosphere (100 times less dense than Earth's), composed mostly of carbon dioxide (CO2), and an arid and sandy surface, full of dunes that move the Martian winds.
However, this desert planet has dense accumulations of ice on its polar caps, large enough to submerge the entire planet under 11 meters of water, if these ices were to melt.
Humanity has observed Mars since ancient times, since it can be seen with the naked eye on a clear night. Astronomy and astrology represents it with the ♂ symbol and, after the Moon, it is one of the most coveted space destinations for human beings in their contemporary space exploration career.
5. Jupiter
Jupiter is the first of the outer planets, that is, those that are beyond the asteroid belt of the solar system. It is a gigantic gaseous planet, surpassed in volume only by the Sun, since Jupiter holds two and a half times the total mass of the rest of the planets combined. Its volume, for example, is 1321 times greater than that of the Earth, but at the same time it is much less dense than it.
Unlike the inner planets, Jupiter does not have a defined surface, but is a ball made up of hydrogen (87%), helium (13%) and other substances such as argon, methane, ammonia and hydrogen sulfide in very small quantities. All these gases are around a rocky core covered by a deep layer of metallic hydrogen in liquid state. This means that there is no clear separation between the atmosphere and the liquid interior of the planet, but that one passes from one to the other gradually.
Jupiter has in the tropical region of its southern hemisphere a huge anticyclone known as the Great Red Spot, first observed in 1664 by the English scientist Robert Hooke (1635-1703). It is a huge whirlpool at least three centuries old, in whose periphery winds of up to 400 kmph have been recorded. Our entire planet would fit twice in this gigantic storm.
The name of this planet pays homage to the father god of the Roman pantheon, equivalent to Zeus of the Greeks, and in astronomy and astrology it is represented by the symbol ♃. Throughout history they have been attributed to around 79 natural satellites of different sizes and shapes, among which the four "Galilee moons" stand out (since Galileo Galilei was the first to observe them): Io, Europa, Ganymede and Callisto.
6. Saturn
Saturn is the sixth planet in the solar system and one of the largest known. Its size and mass are second only to Jupiter, and its ring belt visible from Earth is a very distinctive feature. It was one of the farthest planets observed in ancient times, and was thought to mark the end of the known universe.
Like Jupiter, Saturn is a gas giant, shaped like a sphere flattened at the poles. It is a very sparse planet (it is less dense than water) and with low relative gravity, composed mainly of hydrogen (96%) and helium (3%), as well as scant traces of methane, water vapor and ammonia. . It is unknown whether it has a liquid or rocky core of metallic hydrogen below the outer 30,000 kilometers of its atmosphere.
Saturn has multiple natural satellites, the largest being Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus and Phoebe. These moons lie beyond the ring of material that orbits the planet, made up of millions of smaller particles that spin at 15 times the speed of a bullet.
Saturn's name comes from the Titan of Roman mythology, father of Jupiter and the Olympian gods, whom the ancient Greeks called Cronus, and is represented in astronomy and astrology by the symbol ♄.
7. Uranus
Uranus is the fourth most massive planet in the solar system and, although it is visible to the naked eye in Earth's night sky, it was not discovered until 1781, thus becoming the first planet to be discovered using a telescope. Like Neptune, it has a very different composition from the other two gas giants, which is why these last two planets are often called the “ice giants”.
Its atmosphere is the coldest in the solar system, with an average temperature of -224 °C.This atmosphere is composed of hydrogen and helium, but also water vapor, ammonia, methane and traces of hydrocarbons. In addition, the interior of the planet is composed of a multi-layered ice sheet and a core of frozen rock, but even so it is a very low-density and low-mass planet compared to the others.
A peculiar detail of Uranus has to do with the arrangement of its poles: as its axis of rotation is so tilted, its poles are at the height of what should be the equator. Another detail points to its particular coldness, so accentuated that even Neptune, a planet more distant from the sun, radiates greater temperature.
Uranus also has a ring system comparable to Saturn's, made up of materials of widely varying sizes, from micrometers to almost a meter, arranged in 13 concentric rings just a few kilometers thick.
Uranus receives its name from the original Greek deity that personifies the sky, called by the Romans later Caelus. The astronomical and astrological symbol for this planet is ♅.
8. Neptune
The last planet in the solar system is distant Neptune, an icy giant whose name comes from the Roman god of the sea, equivalent to the Greek god Poseidon. It was the first planet to be discovered thanks to pure mathematical calculations in 1846, and has a very similar composition to that of Uranus, a planet considered to be its "twin". In astronomy and astrology he is represented by the symbol ♆, similar to the trident with which the god of the sea was represented.
Neptune has a small core of rock covered in a frozen crust, all submerged in a thick, dense atmosphere of clouds of hydrogen, helium, water, and methane.The atmosphere is so dense that it reaches pressures almost 100,000 times greater than those experienced on Earth, and its average temperature is -218 °C, receiving very little solar radiation, which points to an internal heat source that is still unknown. with precision.
For the rest, Neptune is a much more dynamic planet than it seems, with an atmosphere full of storms and winds of around 2,200 kilometers per hour, separated into bands of clouds and provided with a blue coloration derived from methane.
It also has a very faint ring system, different from those of Uranus and Saturn, and made up of ice particles, silicates, and very dark organic compounds. To date, three of these outer rings and a very weak sheet of material that extends towards the planet's surface are known. 14 satellites are also known to him so far.
Is Pluto a planet?
For a long time, Pluto was considered the last and farthest planet in the solar system, which seems to be evidenced by its name, referring to the Roman god of the underworld, a variant of Hades of the Greeks.
However, as the exploration and study of the solar system yielded more information about astronomical objects, the organization in charge of standardizing astronomical criteria, the International Astronomical Union (IAU), understood that Pluto has more features in common with Pluto. the other dwarf planets than with the ordinary planets.
These features include its small size, its orbit outside the ecliptic (that is, contrary to that of the rest of the planets), and the presence of Charon, an orbiting companion of the same size and mass discovered in 1978, in addition to other objects. of smaller size that accompany them on their unusual journey through the solar system.Thus, since August 2006, Pluto entered the list of dwarf planets in the solar system, and was no longer considered an ordinary planet.