Solar system; Formation, planets, wonders and everything you need to know

The solar system is one of the billions of star systems in the Milky Way galaxy, which consists of the average central star of the Sun. The order of placement of the planets in this system from the nearest mass to the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and possibly the ninth planet.

The solar system starts from the sun continues to the Kuiper belt and finally reaches the boundary of the Heliopass. According to scientists, the edge of the solar system is approximately 15 billion kilometers away from the sun. On the other side of the Heliopass, there is a huge oval-shaped cloud called the Oort cloud, which surrounds our solar system.

Table of Contents

• What is the solar system?
• The origin of the solar system
• Size and distance in the solar system
• Sun
• The planets of the solar system
• What is a planet?
• Mercury
• Venus
• planet Earth
• planet mars
• Jupiter
• Saturn
• Uranus
• The planet Neptune
• asteroid belt
• Kuiper belt
• Pluto
• The ninth planet
• edge of the solar system
• The largest planets in the solar system
• Discoveries and travels of the solar system
• Photos of the solar system
• Conclusion

What is the solar system?

The solar system is a collection of planets, moons, asteroids, comets, and gas and dust that revolve around the Sun star. This system consists of rocky planets including Mercury, Venus, Earth, and Mars, gas giants including Jupiter and Saturn, and ice giants including Uranus and Neptune.

Between Mars and Jupiter, there is a set of asteroids known as the Asteroid Belt, and on the other side of Neptune, a set of small icy bodies known as the Kuiper Belt revolve around the Sun. Objects such as the dwarf planet Pluto are also considered part of the Kuiper belt.

The origin of the solar system

About 4.6 billion years ago, a dark cloud of gas and dust underwent a gravitational collapse. This cloud compressed and turned into a rotating disk known as the solar nebula. The heat and pressure were eventually so great that the hydrogen atoms fused together to form helium. Nuclear interactions released large amounts of energy and the Sun was formed.

The Sun collected approximately 99% of the material in the solar nebula, and the rest of the material formed similar clumps inside the rotating disk. Some of these materials reached enough mass and gravity to form globular masses or planets, dwarf planets, and moons. The remaining fragments formed meteorites, comets, and other moons that make up the solar system.

Meteorites, or celestial rocks that fell to Earth, helped scientists estimate the age of the solar system. Some of these small fragments originated from moons or planets that can provide fascinating scientific information about the chemical properties and history of their parent matter. Some others were circulating in the solar system from the very beginning and before the formation of planets. The Allende meteorite, which fell to Earth in 1969, is the best-known meteorite with an age of 4.55 billion years.

According to scientists, the solar system was created during the explosion of a nearby star or the supernova process . According to this theory, the explosion caused shock waves to be sent into space and these waves compressed the solar nebula and finally led to its collapse. The supernova likely drove material into the nebula.

The stages of the formation of the solar system

Size and distance in the solar system

The solar system is so big that it is almost impossible to imagine its size using units like kilometers. The distance from the Earth to the Sun is approximately 150 million kilometers, but the distance from the Sun to the farthest planet in the solar system, Neptune, is 4.5 billion kilometers. Now compare this distance with the average distance that a healthy person can walk non-stop in one day (32 km) or the distance to the International Space Station (400 km).

The best way to estimate the size of the solar system is to create a scale model that shows the distance of the planets from the sun. Astronomers use the distance between the Earth and the Sun (150 million kilometers) as a unit of measurement known as the astronomical unit. Therefore, 150 million kilometers is equal to one astronomical unit, or AU for short.

Thus, the distance between Mercury and the Sun (0.43 AU), Venus is 0.7 AU, Earth is 1 AU and Mars is 1.5 AU. Then we reach the asteroid belt, which is 2.8 AU away from the Sun. The gas giants Jupiter and Saturn are 5.2 and 9.5 AU from the Sun, respectively, and the ice giants Uranus and Neptune are 19.8 and 30 AU, respectively.

The Kuiper Belt is 50 AU away from the Sun and finally, the border of the Solar System or Heliopass is 123 AU away from the Sun.

Read More: The International Space Station

Sun

An artist’s rendering of the Parker probe exploring the Sun

The sun is at the center of the solar system and constitutes approximately 99.8% of the mass of its system. The sun provides the necessary energy for life on Earth. This composite yellow dwarf star consists of 91% hydrogen and 8.9% helium. The Sun is relatively small compared to other stars and is one of hundreds of billions of stars in the Milky Way galaxy.

The planets of the solar system

The four inner planets of the solar system, Mercury, Venus, Earth, and Mars, are classified as terrestrial planets or rocky worlds due to their rocky surface.

The four outer worlds of the solar system, namely Jupiter, Saturn, Uranus, and Neptune, are called Jupiter-like planets due to their larger size than the rocky planets. Most of these planets are made up of gases such as hydrogen and helium, although some planetologists believe that some of these planets have solid cores.

The planets Jupiter and Saturn are called gas giants, while Uranus and Neptune, the two outermost worlds of the solar system, are classified as ice giants because they are composed of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur, and have a thick mantle. They have methane, ammonia, and frozen water.

What is a planet?But before introducing the planets of the solar system, it is necessary to get acquainted with the definition of a planet. According to the standard definition, a planet is a mass of sufficient size that revolves around the Sun and itself. But it is not big enough to undergo nuclear fusion like a star. It has also cleared its vicinity of a large number of other objects.

The exact definition mentioned above shows what should be included in the category of planets and what should not be included in this group. However, the problem arose when astronomers discovered a large number of planet-like bodies in the solar system. For example, Pluto was one of the objects that could not meet all the above conditions and was classified as a dwarf planet.

Most of the gaseous planets are composed of hydrogen and helium and probably have a solid core; While the core of rocky planets is often molten.

Pluto’s problem is its small size and strange orbit that cannot clear nearby objects. It also has a lot in common with the Kuiper belt. According to the IAU definition, this planet and other small globular worlds including Eris, Haumea and Makimaki, other Kuiper belt objects are classified as dwarf planets.

Ceres is another globular body in the asteroid belt between Mars and Jupiter, which belongs to the group of dwarf planets. Ceres was classified as a planet when it was first discovered in 1801 but was later recognized as an asteroid. However, this definition was not enough because it was much larger and more spherical than asteroids. Therefore, astronomers classified this object as a dwarf planet in 2006.

Mercury

Mercury is the closest planet to the Sun from the perspective of NASA’s Messenger probe.

• Discovery: It was known to the ancient Greeks and can be seen in the sky with the naked eye.
• Naming: Mercury, derived from the name of the messenger god in Roman mythology
• Diameter: 4878 km
• Year: 88 Earth days
• Day: 58.6 Earth days
• Number of moons: zero

Mercury is the closest world to the sun and the smallest planet in the solar system. This planet is only slightly larger than the Earth’s moon and completes its orbit around the sun in 88 days.

The temperature difference between the day and night of Mercury is significant. The temperature of Mercury during the day reaches 450 degrees Celsius, which is enough to melt lead. During the night, the temperature drops to minus 180 degrees Celsius. Mercury’s atmosphere is very thin and contains elements such as oxygen, sodium, hydrogen, helium, and potassium. Since this weak atmosphere cannot prevent meteorite collisions, Mercury’s surface is full of impact craters, just like Earth’s moon.

During its five-year mission, NASA’s MESSENGER probe made interesting findings about Mercury that defied astronomers’ expectations. One of these findings was the discovery of water ice and frozen biological compounds in the north pole of Mercury, as well as the significant role of volcanic activity in the formation of the planet’s surface.

Venus

This image of Venus was captured in 2020 by NASA’s Mariner 10 probe.

• Discovery: It was known to the ancient Greeks and can be seen with the naked eye.
• Naming: Venus, derived from the name of the goddess of love and beauty in Roman mythology
• Diameter: 12,104 km
• Year: 225 Earth days
• Day: 241 Earth days
• Number of moons: zero

Venus is the second planet from the sun and the hottest planet in the solar system. The thick atmosphere of Venus is composed of compounds such as sulfuric acid clouds. Venus can be considered as one of the clear examples of the greenhouse effect.

The average surface temperature of Venus reaches 465 degrees Celsius and its surface pressure is 92 bar (9200 kilopascals), which can disintegrate a human being. Strangest of all, Venus rotates slowly and rotates against the direction of other planets, i.e. from east to west.

Venus is sometimes called Earth’s twin because the planet is close in size to Earth and, based on radar images, has numerous mountains and volcanoes. But in reality, Earth and Venus have many differences from each other.

Since Venus is the brightest object in the night sky after the moon, the Greeks thought that they were two different objects; Hesperus as a night star and Eospherus as a morning star. This very brightness is why Venus is sometimes mistaken for a UFO.

planet Earth

One of the most accurate pictures of the Earth. This composite image is the result of images recorded by the Processing Infrared/Visible Image Radiometer (VIIRS) of the Suomi NPP satellite.

• Name: Earth is derived from the German word “Die Erde” which means earth.
• Diameter: 12,760 km
• Year: 365.24 days
• Day: 23 hours and 56 minutes
• Number of moons: 1

Earth, our home, is the third planet from the Sun. Earth is a blue world with two-thirds of it covered by water. Earth’s atmosphere is rich in nitrogen and oxygen, making it the only life-friendly world we know.

The earth rotates at a speed of 467 meters per second. But this speed is slightly higher in the equator. The speed of the earth’s rotation around the sun reaches 29 km/s. Earth is also the largest rocky planet in the solar system and has one moon. According to scientists, an object hit the earth early in its formation and a piece of it was thrown into the sky and thus the moon was formed.

planet Mars

A mosaic image of the Vals Marineris hemisphere of Mars. This image is the result of combining 102 Viking orbiter images.

• Discovery: It was known to the ancient Greeks and can be seen with the naked eye.
• Name: Mars, derived from the name of the god of war in Roman mythology
• Diameter: 6787 km
• Year: 687 Earth days
• Day: 24 hours and 37 minutes
• Number of moons: 2

Mars is the fourth planet from the Sun. This desert-like and cold planet is covered with iron oxide dust and therefore appears red. Mars has similarities with Earth. It is primarily rocky like Earth, has mountains and valleys, and has a storm system like Earth’s, ranging from small tornado-like ovens to dust storms that cover the entire planet.

Scientific evidence shows that Mars was a warmer and wetter world billions of years ago, and probably had rivers and maybe oceans flowing in it. Although the Martian atmosphere is too thin for surface liquid water to flow, wetter Martian remnants exist today. Martian ice sheets the size of the state of California are located under the surface of Mars, and on the other hand, both poles of Mars have water ice covers.

According to scientists, ancient Mars had the necessary conditions to support life such as bacteria and other microbes. They hope to find signs of this past life and possibly present life forms. This hypothesis became the basis for launching several missions to Mars; So that today the red planet is one of the most familiar and most explored objects in the solar system.

Jupiter

An extraordinary image of Jupiter captured by the Hubble Space Telescope on August 25, 2020.

• Discovery: It was known to the ancient Greeks and can be seen with the naked eye.
• Naming: Jupiter, derived from the name of the god of gods in Roman mythology
• Diameter: 139,822 km
• Year: 11.9 Earth years
• Day: 9.8 Earth hours
• Number of moons: 95

Jupiter is the fifth planet from the sun and the largest planet in the solar system. This gas giant has twice the mass of all other planets in the solar system.

Jupiter’s swirling clouds are colorful due to the combination of a variety of materials such as ammonia ice, ammonium hydrosulfide crystals, and water ice and vapor. One of Jupiter’s most famous features in its swirling clouds is the Great Red Spot, which is more than 16,000 kilometers in diameter and is so large that it can swallow almost three Earths.

Jupiter also has the strongest magnetic field and 95 moons, the most famous of which are Ganymede, Io, Callisto, and Europa, also known as the Galilean moons.

Saturn

The Hubble Space Telescope captured this image of Saturn during the Northern Hemisphere summer on July 4, 2020.

• Discovery: It was known to the ancient Greeks and can be seen in the night sky with the naked eye.
• Naming: Saturn, derived from the name of the god of agriculture in Roman mythology
• Diameter: 120,500 km
• Year: 29.5 Earth years
• Day: approximately 10.5 hours by land
• Number of moons: 145 moons

Saturn, the sixth planet from the Sun, is famous for its huge and bright ring system. Although Saturn is not the only ringed planet in the solar system. When Galileo first studied Saturn in the early 1600s, he thought it was a three-part mass: a planet and two large moons on either side. He didn’t know he was seeing a ringed planet. More than 40 years later, Christian Huygens proved the existence of Saturn’s rings.

Like Jupiter, Saturn is a gas giant and the least dense planet in the solar system. This planet also has a large number of moons, according to the latest statistics, their number reaches 145. With this number of moons, Saturn is considered the king of the solar system’s moons. Enceladus is one of Saturn’s moons covered with an icy ocean, which astronomers say could be a promising target for extraterrestrial life.

Saturn’s rings are composed mostly of ice and rock, and scientists are still unsure how they formed.

Uranus

Image of Uranus captured by NASA’s Chandra X-ray Observatory.

• Discovery: 1781 by William Herschel (before this date people thought Uranus was a star).
• Naming: the embodiment of heaven and the name of one of the gods in Greek mythology
• Diameter: 51,120 km
• Year: 84 Earth years
• Day: 18 hours on land
• Number of moons: 27

The planet Uranus, the seventh planet from the sun, has strange and unique features. The clouds of Uranus are composed of hydrogen sulfide, which is the same chemical that causes eggs to rot and smell bad. In the second degree, like Venus, Uranus rotates from east to west, but unlike Venus or any other planet, its equator is perpendicular to its orbit and it can be said to rotate sideways.

According to astronomers, a mass twice the size of Earth collided with Uranus about 4 billion years ago and caused Uranus’ extreme axial deviation. This deviation leads to marginal seasons with a duration of at least 20 years, so that sunlight shines on one pole of Uranus for 84 years.

It seems that the said collision transferred some of the rock and ice of Uranus into its orbit and these rocks and ice later formed the moons of Uranus. Methane in the atmosphere of Uranus is the main reason for its blue-green color. Uranus has 13 sets of rings.

The planet Uranus also holds the record for the coldest temperature recorded in the solar system, minus 224.2 degrees Celsius. The average temperature of Uranus reaches minus 195 degrees Celsius.

The planet Neptune

Neptune is the planet with the fastest winds in the solar system.

• Discovery: 1846
• Naming: Neptune, derived from the name of the god of water and sea in Roman mythology
• Diameter: 49,530 km
• Year: 165 Earth years
• Day: 19 hours on land
• Number of moons: 14

Neptune is the eighth and farthest planet from the Sun. The average temperature of Neptune in the upper part of the clouds reaches minus 210 degrees Celsius. This planet is about the same size as Uranus and is known for its strong supersonic winds.

Neptune was the first planet to be discovered using mathematics. German astronomer Johann Galle used mathematical calculations to find Neptune with a telescope.

Neptune is about 17 times heavier than Earth and has a rocky core. The main composition of Neptune is water, methane, and ammonia, which surround this rocky core. The speed of Neptune’s winds reaches 2000 km/h. This planet also has 14 moons.

asteroid belt

The asteroid belt is located between Mars and Jupiter. According to NASA estimates, there are between 1.1 and 1.9 million asteroids in the main asteroid belt that are larger than one kilometer in diameter. The dwarf planet Ceres with a diameter of approximately 950 km is located in this part of the solar system. Several asteroids have orbits that occasionally collide with Earth and other inner planets.

Kuiper belt

Astronomers have long suspected the existence of a band of icy material known as the Kuiper Belt, which lies beyond the orbit of Neptune at a distance of 30 to 55 times the distance from the Earth to the Sun. Since the 20th century, more than a thousand crimes have been discovered in this belt. According to scientists’ estimates, the Kuiper Belt probably hosts hundreds of thousands of icy bodies larger than 100 km, as well as almost a trillion comets.

Pluto, which today belongs to the group of dwarf planets, is located in the Kuiper belt. Of course, Pluto is not the only one, and Makimaki, Haumea, Eris, and Quavar are among the other known non-Neptunian objects from the group of dwarf planets. Aracut (Altima Tully) is also a binary asteroid located in the Kuiper Belt that was visited by the New Horizons probe in 2019.

Pluto

A panoramic view of the dwarf planet Pluto

• Discovered: 1930 by Clyde Tamba
• Naming: Pluto or Pluton derived from the name of the god of the underworld in Roman mythology
• Diameter: 2301 km
• Year: 248 Earth years
• Day: 6.4 Earth days
• Number of moons: 5

The dwarf planet Pluto was once considered the ninth planet, but since 2006 it has been classified as a dwarf planet. The reason for this problem was the non-compliance with the existing criteria in the definition of the planet. According to the definition of the International Astronomical Union, a planet is a celestial body that firstly orbits the Sun, secondly has enough gravity to become a spherical or almost spherical body, and thirdly clears the vicinity of its orbit. be Pluto did not fit the third criterion of logic and therefore was removed from the group of planets.

Pluto has a highly elliptical orbit so it sometimes even interferes with Neptune’s orbit. On the other hand, Pluto’s orbit is not in the same plane as other planets, but it revolves around the Sun at an angle of 17.1 degrees above or below them.

Because of this strange orbit, Pluto was considered the eighth planet from the Sun from 1979 to early 1999, but on February 11, 1999, when it crossed the path of Neptune, it again became the most distant planet in the Solar System, until it was officially removed from the Sun in 2006. The group of planets is out.

Smaller than Earth’s moon, Pluto is a cold, rocky world with a thin atmosphere. On July 14, 2015, the New Horizons probe performed several low-altitude flybys around Pluto, presenting a new view of the dwarf planet to the scientific world that defied many expectations.

Pluto is actually a very active ice world, covered in glaciers, ice mountains, icebergs, and possibly even glaciers that spew ice made of water, methane, or ammonia.

The ninth planet

According to estimates, the hypothetical ninth planet has approximately 10 times the mass of Earth.

In 2016, researchers raised the possibility of the ninth planet . This object, also known as Planet X, is estimated to have 10 times the mass of Earth and orbits the star of our system at a distance between 300 and 1,000 times the distance between Earth and the Sun. In fact, this planet’s year may last between 10,000 and 20,000 Earth years. Scientists have not been able to observe the ninth planet so far and have guessed its existence based on its gravitational effects on other objects in the Kuiper belt.

According to some hypotheses, the hypothetical ninth planet could be a primordial black hole that formed shortly after the Big Bang and was trapped by the solar system. Unlike black holes that result from the collapse of massive stars, primordial black holes were formed by gravitational perturbations less than a second after the Big Bang and may be very small (as little as five centimeters in diameter), making them difficult to detect.

Astronomers have not yet reached a clear conclusion regarding the ninth planet. Based on a 2022 survey by the ACT telescope in Chile, there are thousands of candidate sources for the planet, but none have yet been confirmed.

Edge of the solar system

The heliosphere surrounds the solar system like a bubble and its boundary is called the heliopass.

By passing through the Kuiper belt, we reach the edge of the solar system or the Heliopass. The heliosphere is a vast, tear-shaped region of space with a large amount of charged particles received from the sun. According to many astronomers, the boundary of the heliosphere, which is called the heliopass, is approximately 15 billion kilometers from the sun.

The Oort cloud is located after the Kuiper belt at a distance of 2,000 to 2,500 AU from the Sun, and the distance of its outer edge from the Sun is estimated to be between 10,000 and 100,000 AU. As mentioned in the previous sections, one astronomical unit is approximately equal to 150 million kilometers. The Everett Cloud is home to billions or perhaps trillions of particles.

The largest planets in the solar system

Jupiter compared to other planets

Jupiter is by far the largest planet in the solar system, so if you add the mass of all the planets in the solar system together, Jupiter will still be two and a half times more. Compared to Earth, Jupiter is 318 times the size of Earth. The radius of this planet reaches 69,911 km or one-tenth of the sun. Saturn is the second largest planet in the solar system. Saturn has 95 times the mass of Earth; however, it is the least dense planet in the solar system, so that it can float on water.

Discoveries and travels of the solar system

According to NASA, more than 254 probes have left Earth’s orbit so far. A large part of these spacecrafts and probes were dedicated to the exploration of the solar system.

Parker probe is the only spacecraft that managed to reach the closest distance to the Sun and will break this record in the coming years. The probe will release information about the solar radiation, surface, corona, and solar wind.

Famous probes such as NASA’s MESSENGER, Mariner 10, and Beppy Columbo have visited Mercury and revealed valuable information such as the discovery of water ice and the thin atmosphere of Mercury.

In general, 46 probes have visited Venus so far, the most successful of which are the Venus Express, Mariner 10, and Magellan missions. These probes released information about the atmosphere of Venus and its possible volcanic activity.

There are many satellites in the earth’s orbit whose task is to check weather and atmospheric conditions. Also, the International Space Station is the largest man-made structure in space, and astronauts are engaged in research work there.

In the last 60 years, six lunar landers have landed on the surface of the moon, the first of which was the Apollo 11 mission. Also, in recent years, orbiters were placed in the orbit of the moon, whose most important achievement was finding water ice around the poles of the moon. Space agencies aim to land on the surface of the Moon again in the coming years and use the Earth’s moon as a research base.

Apollo 11, the first human landing on another world.

Mars is the most explored planet in the solar system, which has been assigned more than 50 exploration missions. The most famous Mars missions include the Curiosity rover, Perseverance, and the MRO orbiter. Each of the Mars rovers and probes is investigating a certain area and so far they have published important and valuable data such as the discovery of water ice, polar ice cover, and methane on Mars. In the not-too-distant future, human explorations will be added to this collection.

Among the outer planets of the solar system, Jupiter and Saturn are two of the most explored examples. So far, eight spacecraft have been sent specifically to visit Jupiter, and two other probes have performed low-altitude flybys of the planet. The Juno probe is still in Jupiter’s orbit and has provided valuable information about Jupiter’s atmosphere and its important moons.

Voyager 2, is the first and so far the only probe to visit the planets Uranus and Neptune.

Cassini is the most famous probe that visited Saturn, and in addition to recording beautiful images of Saturn and sending information about its atmospheric conditions and rings, it investigated two important moons of Saturn, Titan and Enceladus. Two of Cassini’s most important discoveries in visiting these moons were the discovery of methane lakes on Titan and glaciers and ice oceans on Enceladus.

The two famous probes Voyager 1 and 2 successfully visited the outer planets of the outer solar system, including Jupiter, Saturn, Uranus, and Neptune. Voyager 2 is the only probe that visited Uranus and Neptune up close.

New Horizons is the only probe to visit the dwarf planet Pluto, sending back important information about surface conditions, moons, and other Kuiper Belt objects.

In addition to the probes that visited the planets of the solar system, a series of missions were dedicated to the study of objects in the asteroid belt. Also, the Hubble and James Webb telescopes have sent important images and data from the solar system.

Conclusion

The solar system is a collection of planets, moons, asteroids, and comets around the sun. The planets of the solar system are divided into two groups: rocky and gaseous planets. Earth is a rocky planet and the only planet known to host life in the entire universe. So far, many probes have been sent to different planets of the solar system. Meanwhile, Mars is considered the most explored and familiar planet of the solar system, which mankind has made the most efforts to investigate. Today, humans are carrying out missions and building new probes to investigate the potential of life on the planets and moons of the solar system, and in this way, they will get help from ground and space telescopes.