The solar system (or solar system) is a planetary system with the Sun at the center and celestial bodies under the gravitational pull of the Sun, all of which were formed from the collapse of a meteor cloud and a giant asteroid almost 4.6 billion years ago. Most celestial bodies revolve around the Sun, and their mass is concentrated mainly on 8 planets with almost circular orbits and orbital planes that closely coincide with each other, called the plane of the ecliptic. The four smaller inner planets include: Mercury, Venus, Earth, and Mars – they are also called rocky planets because they are composed primarily of rock and metal. The four outer gas giant planets are much more massive than the four inner planets. The two largest planets, Jupiter and Saturn, are composed mainly of helium and hydrogen; and the two most distant planets, Uranus and Neptune, are composed primarily of ice, such as water, ammonia, and methane, and are sometimes classified as ice giants. There are six planets and three dwarf planets with natural satellites in orbit. These satellites are called “Moons”, after the Earth’s Moon. Each outer planet also has planetary rings containing dust, particles, and small objects in orbit.
Solar system also contains two regions with concentrations of smaller celestial bodies. The asteroid belt, located between Mars and Jupiter, has a composition similar to that of the rocky planets with mainly rocks and metals. Outside Neptune’s orbit are extra-Neptunian objects composed primarily of ice such as water, ammonia, and methane. Between these two regions there are five typically sized celestial bodies, Ceres, Pluto, Haumea, Makemake and Eris, which are considered large enough to be spherical under the influence of their own gravity, and astronomers classify them as dwarf planets . Additionally, there are thousands of small celestial bodies located between these two regions, varying in size, such as comets, centaurs and interplanetary dust, which move freely between these two regions.
The Sun emits streams of plasma matter, called solar wind, which create a bubble of stellar wind in the interstellar medium called the heliosphere, which extends to the edge of the scattered disk. The hypothetical Oort Cloud, considered a source of long-period comets, could exist at distances nearly 1,000 times that of the heliosphere.
The Sun is the central and most important star in the solar system. Its enormous mass (332,900 times the mass of Earth) creates enough temperature and density at the core for nuclear fusion to occur, releasing enormous amounts of energy, much of which is emitted into the atmosphere beneath form of electromagnetic radiation, peaking in the 400 to 700 nm spectral range that we call visible light.
The Sun is classified as a G2 yellow dwarf, but this name often causes misunderstanding when compared to the vast majority of stars in the Milky Way, the Sun is a large and bright star. Stars are classified according to the Hertzsprung-Russell diagram, which represents the brightness of a star as a function of its surface temperature. In general, brighter stars are hotter. The Sun is located to the right of the middle of a band called the main band on the chart. However, the number of stars brighter and hotter than the Sun is rare, while the majority are dimmer, cooler stars, called red dwarfs, which make up 85% of the galaxy’s star count.
It is believed that with the Sun’s position on the main sequence it is a “lively” star, it has not yet exhausted its hydrogen fuel source for nuclear fusion reactions. The Sun becomes brighter; At the beginning of its evolution, its luminosity was only 70% greater than today.
The four inner planets are high-density rocky planets, with a rocky composition, little or no Moon, and no orbiting ring systems like the outer planets. Their main components are refractory minerals, like the silicates that make up their crust and mantle, and metals like iron and nickel that make up their core. Three of the four planets (Venus, Earth and Mars) have atmospheres thick enough to produce weather phenomena; all have impact craters and surface tectonic zones such as rift valleys and volcanoes. Terms inner planet should not be confused with inner planetrefers to planets closer to the Sun than to Earth (such as Venus and Mercury).
Mercury (about 0.4 AU from the Sun) is the closest planet to the Sun and the smallest planet in the Solar System (0.055 times the mass of Earth). Mercury has no natural satellites and its only geological features, besides impact craters, are slopes and cliffs, probably formed early in the contraction phase of its history. Mercury has almost no atmosphere because the atoms in its atmosphere were blown into space by the solar wind. The planet has a relatively large iron core and a fairly thin mantle that has not yet been discovered by scientists and is not fully explained by astronomy. It is assumed that the outer mantle was torn away by a giant impact and that accretion of material by Mercury was prevented by the energy of the young Sun.
Venus (about 0.7 AU from the Sun) is quite close in size to the size of Earth (with a mass equal to 0.815 times the mass of Earth) and structural characteristics similar to Earth, it has a thick layer of silicate surrounding an iron core. . Venus has a thick atmosphere and there is evidence that the planet is home to geological activity. However, Venus is much drier than Earth and the density of its atmosphere is 90 times greater than that of Earth. Venus has no natural satellites. It is the hottest planet in the solar system with an atmospheric temperature above 400°C, mainly due to the greenhouse effect of the atmosphere. No specific signs of recent geological activity have been identified. a thick atmosphere), however the planet does not have a magnetic field to prevent significant atmospheric deterioration, which suggests that the contents of the atmosphere are regularly replenished by volcanic eruptions.
Earth (1 AU from the Sun) is the largest and densest of the inner planets, it is also the only planet to our knowledge that has had recent geological activity and it is the only known planet in the universe to harbor life. is also the only rocky planet with a liquid hydrosphere and the only planet where plate tectonics have been observed. Earth’s atmosphere is also fundamentally different from other planets, with free oxygen molecules essential for life making up 21% of the atmosphere. The Earth has a natural satellite, the Moon, which is the largest natural satellite of the rocky planets in the solar system.
Mars (about 1.5 AU from the Sun) is smaller than Earth and Venus (the mass is 0.107 times the mass of Earth). Its atmosphere is made up mainly of carbon dioxide and its surface atmospheric pressure is 6.1 millibars (about 0.6% of the atmospheric pressure at the Earth’s surface). On the surface of the Red Planet are giant mountains like Olympus Mons (the tallest in the solar system) and chains of valleys like Valles Marineris, with geological activity that may have existed up to 2 million years ago. years. Its surface is red because there is a lot of iron oxide (rust) in the surface soil. Mars has two very small moons (Deimos and Phobos) which are believed to be asteroids captured by Mars.
The four outer planets, or four gas giants (or Jupiter-like planets), make up 99% of the total mass of bodies orbiting the Sun.[c] Jupiter and Saturn are the two largest planets and contain the vast majority of hydrogen and helium; Uranus and Neptune are less massive (<20 times the mass of Earth) and contain more ice. For this reason, some astronomers consider them to belong to a class of “ice giants”. The four gas giants all have a ring system, although only Saturn's rings are visible from Earth through amateur telescopes. The term outer planets should not be confused with the term outer planets, which refers to planets beyond Earth's orbit, which includes Mars and the outer planets.
Jupiter (distance from the Sun 5.2 AU), with a mass equal to 318 times the mass of Earth and 2.5 times the total mass of the 7 remaining planets in the solar system. Jupiter is composed mainly of hydrogen and helium. The enormous heat coming from Jupiter’s interior creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot.
Jupiter has 63 known satellites. The four largest moons, Ganymede, Callisto, Io and Europa (the moons of Galilee) exhibit characteristics similar to those of rocky planets, such as volcanism and internal heat. Ganymede, the largest natural satellite in the solar system, is larger than Mercury.
Saturn (distance from the Sun 9.5 AU) has markedly different characteristics, a very large ring system and similar characteristics to Jupiter, such as the composition of the atmosphere and the magnetosphere. Although Saturn is 60% the volume of Jupiter, its mass is only one-third that of Jupiter, or 95 times the mass of Earth, making it the least dense planet in the solar system (lower to the density of liquid water). Saturn’s rings contain dust as well as small particles of ice and rock.
Saturn has 62 confirmed natural satellites; two of them, Titan and Enceladus, show signs of geological activity, although they are ice volcanoes. Titan, the second largest natural satellite in the solar system, is also larger than Mercury and Enceladus. is the only satellite in the solar system to have a significant atmosphere.
Uranus (distance from the Sun 19.6 AU), mass 14 times greater than that of Earth, is the lightest outer planet. Its axis of rotation has a unique feature compared to other planets, the inclination of the axis is greater than 90 degrees with respect to the plane of the ecliptic. Uranus has a much colder core than other gas giants, and the amount of heat radiated into space is also small.
Uranus has 27 known natural satellites, the largest, from largest to smallest, being Titania, Oberon, Umbriel, Ariel and Miranda.
Neptune (distance from the Sun 30 AU), although slightly smaller than Uranus, is more massive (17 times the mass of the Earth) and therefore denser. It also emits more heat, but not as much as that of Jupiter or Saturn.
Neptune has 13 known natural satellites. Triton is the largest satellite and is geologically active with liquid nitrogen geysers. Triton is also the only natural satellite with a retrograde orbit. Also in the same orbit of Neptune are a number of minor planets, called Neptune Trojans, which are in 1:1 orbital resonance with Neptune.