Planets of the solar system: 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 is part, along with seven other known planets: Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune.
Broadly speaking, the planets are large spherical masses of compact matter that orbit the Sun in regular periods, some of them composed of solid elements, others of gaseous accumulations. The Sun’s immense gravitational force keeps them in their respective orbits, whose location allows them to be classified into two subsets: the inner planets and the outer planets. You must read about Social Actors once.
The inner planets
This first group is made up of Mercury, Venus, Earth and Mars, distributed between the Sun and the asteroid belt after Mars. They are smaller planets with solid surfaces, which move in shorter and faster orbits. Of these, only Mars and Earth have their own satellites.
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 most distant part of the solar system. They are larger planets with a 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 planets orbit the Sun, other small celestial bodies, known as natural satellites, orbit 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 firmament. It occupies 99.86% of the mass of the solar system and is a type-G star that crosses its main sequence, with a diameter of 149,597,870.7 km.
Dwarf planets:
In addition to the eight known planets, there are five dwarf planets, with similar properties but much smaller in size and little orbital dominance (that is, they can share their orbits with other objects).
Minor bodies:
This is the name given to clusters 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 a light year from the Sun.
Finally, it is important to understand that the solar system is not a static place, but that it moves within a larger system that is the galaxy, and that in our case we have named the Milky Way. Within this galaxy, our solar system is located in a peripheral region, at the end of one of its spirals. Maybe you should definitely read about Social Impact once.
Formation of the solar system
According to scientific estimates, the solar system was 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 out to form a protoplanetary disk, that is, a disk of matter around a young star, from which the planets and asteroids emerged much later.
This explanation responds to the theory proposed in the 18th century by Emmanuel Swedenborg (1688-1772), Immanuel Kant (1724-1804) and Pierre-Simon Laplace (1749-1827), although in later centuries (especially in the 20th century, with the beginning of space exploration) it was refined and redefined to incorporate the most recent discoveries and observations in space matters.
From its earliest days, the solar system has evolved and transformed intensely, as a result of the ejection of materials from the Sun, and also of the numerous collisions that occurred between objects born from the planetary protodisk, or also from outside the solar system. But gradual cooling was necessary (especially of the inner solar system) so that unions of very volatile molecules could emerge and rocky planets, such as ours, could be formed.
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 them has to do, according to the International Astronomical Association, with three main features:
- A planet must orbit around the Sun (and not other astronomical objects in the solar system);
- A planet must have enough mass 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 celestial bodies.
Therefore, there are eight planets in the solar system (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune) and five dwarf planets (Pluto, Ceres, Eris, Haumea and Makemake).
The planets, however, are masses in constant motion, which complete their journey around the Sun (that is, their translational movement) at different times: the farther away 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 rotational movement) at a different rate and in a uniform direction (except for Venus and Uranus, which rotate “backwards”). 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 the known planets gives data such as the following:
Planets Short Information-
Mercury:
- Diameter at the equator (km) – 4,879.4 km
- Distance from the Sun (km) – 57,910,000 km
- Number of satellites – 0
- Time to make one rotation – 58.6 days
- Time to make one translation – 87.97 days
Venus:
- Diameter at the equator (km) – 12,104 km
- Distance from the Sun (km) – 108,200,000 km
- Number of satellites – 0
- Time to make one rotation – 243 days
- Time to make one translation – 224.7 days
Earth:
- Diameter at the equator (km) – 12,742 km
- Distance from the Sun (km) – 149,600,000 km
- Number of satellites – 1
- Time to rotate – 23.93 hours
- Time to rotate – 365.2 days
Mars:
- Diameter at the equator (km) – 6,779 km
- Distance from the Sun (km) – 227,940,000 km
- Number of satellites – 2
- Time to rotate – 24.62 hours
- Time to rotate – 686.98 days
Jupiter:
- Diameter at the equator (km) – 139,820 km
- Distance from the Sun (km) – 778,330,000 km
- Number of satellites – 79
- Time to rotate – 9.84 hours
- Time to rotate – 11.86 years
Saturn:
- Diameter at the equator (km) – 116,460 km
- Distance from the Sun (km) – 1,429,400,000 km
- Number of satellites – 82
- Time to make one rotation – 10.23 hours
- Time to make one translation – 29.46 years
Uranus:
- Diameter at the equator (km) – 50,724 km
- Distance from the Sun (km) – 2,870,990,000 km
- Number of satellites – 27
- Time to make one rotation – 17.9 hours
- Time to make one translation – 84.01 years
Neptune:
- Diameter at the equator (km) – 49,244 km
- Distance from the Sun (km) – 4,504,300,000 km
- Number of satellites – 14
- Time to complete one rotation – 16.11 hours
- Time to complete one translation – 164.8 years
Planets of the Solar System
1. Mercury
Represented astronomically and astrologically by the symbol ☿, Mercury is the planet closest to the Sun and the smallest of all the inner planets. Lacking natural satellites, it is a rocky planet, made up of 70% metallic elements (iron in particular) and the remaining 30% of various silicates, making it the second densest planet in the entire solar system, after Earth.
Mercury has a dry surface full of impact craters from 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 back to the earliest antiquity (the 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 given to it by the Greeks when they observed it at dusk, while in the morning sky they called it 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 astronomy and astrology, Venus is an inner planet that lacks satellites and is the second brightest object on Earth at night (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 dense atmosphere of carbon dioxide (CO2), molecular nitrogen (N2) and hydrogen sulfide (H2S), which are known greenhouse gases. For this reason, Venus is the hottest planet in the solar system, much hotter than Mercury, despite the latter being closer to the Sun. Its average temperature is 463.85 °C.
This atmosphere also gives Venus a yellowish white color, and an atmospheric pressure 90 times greater than that of Earth. On the other hand, its rotation movement is particularly slow (and contrary to that of most planets), so that on Venus a day lasts much 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. Earth
The Earth, our planet, is quite exceptional compared to the rest of the solar system. Not only because we are the only living beings we know of that are on it, but because it is the only planet that has liquid water and a flourishing biosphere that has been around 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 makes it neither too hot nor too cold.
It is the densest planet in the entire solar system, and the fifth largest in proportion. The Earth has an iron and nickel core whose internal movements generate a powerful magnetosphere, and at the same time a not too dense atmosphere, composed of 78% nitrogen, 21% oxygen and the rest other substances such as argon, carbon dioxide, ozone and water vapour. Thanks to the heat retention of the atmosphere, the planet has a mild and stable climate, otherwise its average temperatures would be around -18 °C.
71% of the Earth’s surface is covered by water, particularly by the salt water of the oceans, and the hydrological cycle is what keeps the atmosphere cool and stable, in addition to the exchange of elements that led to the emergence of life. The Earth has a single 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 Gea, 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 the Greek Ares, and also known as the “red planet” due to the abundant iron oxide on its surface. It has two natural satellites, small and irregularly shaped, called Phobos (from the Greek phobos, “fear”) and Deimos (from the Greek deimos, “terror”), whose origin is unknown but which could be asteroids captured by the planet’s gravity.
It is a smaller planet than Earth, but it shares numerous 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, sandy surface, full of dunes moved by the Martian winds.
However, this desert planet has dense accumulations of ice in its polar caps, large enough to flood the entire planet under 11 meters of water, if these ices could melt.
Mankind has observed Mars since ancient times, since it can be seen with the naked eye on a clear night. Astronomy and astrology represent it with the symbol ♂ and, after the Moon, it is one of the most coveted space destinations for humans in their contemporary race for space exploration.
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 can hold 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 composed of hydrogen (87%), helium (13%) and other substances such as argon, methane, ammonia and hydrogen sulphide in very small quantities. All these gases are around a rocky core covered by a deep layer of metallic hydrogen in a liquid state. This means that there is no clear separation between the atmosphere and the liquid interior of the planet, but rather 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, on whose periphery winds of up to 400 km/h have been recorded. This gigantic storm would fit twice our entire planet.
The name of this planet pays homage to the father god of the Roman pantheon, equivalent to the Zeus of the Greeks, and in astronomy and astrology it is represented by the symbol ♃. Throughout history, around 79 natural satellites of different sizes and shapes have been attributed to it, among which the four “Galilean 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 only surpassed by Jupiter, and its ring belt visible from Earth is a very characteristic feature. It was one of the most distant planets observed in ancient times, and it 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 low-density planet (less dense than water) with low relative gravity, composed mainly of hydrogen (96%) and helium (3%), as well as scarce traces of methane, water vapour and ammonia. It is unknown whether it has a liquid or rocky core of metallic hydrogen beneath the outer 30,000 kilometres of its atmosphere.
Saturn has multiple natural satellites, the largest of which are Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus and Phoebe. These moons are located beyond the ring of materials that orbits the planet, composed of millions of smaller particles that rotate at a speed 15 times faster than that of a bullet.
The name Saturn 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 the Earth’s night sky, it was not discovered until 1781, making it 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 mantle of ice 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: because its axis of rotation is so inclined, 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 farther from the sun, radiates a higher temperature.
Uranus also has a ring system comparable to that of Saturn, composed of materials of very variable size, from micrometers to almost a meter, organized in 13 concentric rings of just a few kilometers thick.
Uranus receives its name from the primeval Greek deity who personifies the sky, later called Caelus by the Romans. The astronomical and astrological symbol for this planet is ♅.
8. Neptune
The last planet in the solar system is the 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 through pure mathematical calculations in 1846, and has a composition very similar to that of Uranus, the planet considered to be its “twin.” In astronomy and astrology it is represented by the symbol ♆, similar to the trident with which the god of the sea was represented.
Neptune has a small rock core covered by a frozen crust, all submerged in a thick and 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, as it receives very little solar radiation, which points to an internal heat source that is still unknown exactly.
Neptune is a much more dynamic planet than it might seem, 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 color derived from methane.
It also has a very weak ring system, different from those of Uranus and Saturn, and made up of ice particles, silicates and organic compounds of very dark color. To date, three of these outer rings are known and a very weak layer of materials that extends towards the surface of the planet. It also has 14 known satellites so far.
Is Pluto a planet?
For a long time, Pluto was considered the last and most distant planet in the solar system, something that seems to be evidenced by its name, referring to the Roman god of the underworld, a variant of the Hades of the Greeks.
However, as exploration and study of the solar system yielded more information about astronomical objects, the International Astronomical Union (IAU) – the organization in charge of standardizing astronomical criteria – came to understand that Pluto has more features in common with other dwarf planets than with ordinary planets.
These features include its small size, its orbit outside the ecliptic (that is, opposite 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, as well as other smaller objects that accompany it on its unusual journey through the solar system. Thus, since August 2006, Pluto entered the list of dwarf planets in the solar system, and is no longer considered an ordinary planet.
