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



Solar system
The solar system is one of the billions of star systems of the Milky Way galaxy, which includes eight planets and a huge collection of comets and asteroids.

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.

Solar system

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.

Solar system

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


Solar system

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.

Solar system

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.


Solar system

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.


Solar system


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

Solar system

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

Solar system

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.


Solar system

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.


Solar system

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.


Solar system

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

Solar system

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.


Solar system

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

Solar system

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

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.

Solar system

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.

Solar system

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.


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.


Fermi’s paradox; Where are the extraterrestrials?




Fermi's paradox
Fermi’s paradox refers to the contradiction between the high probability of extraterrestrial intelligence in the universe and the fact that we have no conclusive evidence for the existence of such aliens.

Fermi’s paradox; Where are the extraterrestrials?

From NASA’s efforts to scientifically study UFOs or unidentified flying objects to the unveiling of alien bodies in Mexico , these days extraterrestrial intelligence has apparently become a more serious issue for politicians, researchers and the public. Although decades have passed since the first sighting of UFOs in the skies, there is still no evidence that definitively points to their extraterrestrial origin.

We’ve also been listening to space radio signals since about the middle of the last century, maybe for a message from aliens. On the other hand, for decades we have been trying to find extraterrestrial life in its very simple form in our own cosmic neighborhood by sending various spacecraft; But we still haven’t found any sure sign of extraterrestrial life. But how can we be really alone in such a big world?

Table of Contents
  • What is Fermi’s paradox?
  • The abundance of potentially habitable worlds
  • Drake’s equation
  • Large filter
  • Possible answers to Fermi’s paradox
  • Aliens are not advanced yet
  • Life is fragile
  • Intelligent life destroys itself
  • Other answers

What is Fermi’s paradox?

Given that our solar system is very young at approximately 4.5 billion years old compared to the 13.8 billion year old universe, and that interstellar travel may have been relatively easy to achieve over this long period of time, aliens would have to Today they were meeting the earth. But as far as we know, there has been no contact between us and extraterrestrials yet. As a result, the question arises, where are the aliens?

The contradiction between the high probability of the existence of alien intelligence and the lack of evidence for the existence of such aliens is called Fermi’s paradox. This paradox takes its name from Enrico Fermi, a renowned physicist who won the Nobel Prize. Fermi apparently made the above points in 1950 during a casual lunchtime conversation.

Enrico Fermi in his laboratory
Enrico Fermi in his laboratory.

The Search for Extraterrestrial Intelligence (SETI) Institute in California explains the paradox: “Farmey found that any civilization with a moderate level of rocket technology and colonialist motives could quickly colonize the entire galaxy. Over the course of a few tens of millions of years, any star system could be dominated by an empire. Tens of millions of years may seem like a long time, But it is very short compared to the age of the galaxy (which is almost a thousand times longer).”

Fermi died in 1954; As a result, other scientists were responsible for investigating and explaining his idea. One of these people was Michael Hart, an American astrophysicist who published an article in 1975 titled ” An Explanation for the Absence of Extraterrestrials on Earth ” in the Quarterly Journal of the Royal Astronomical Society (RAS). According to some, Hart’s article is the first research that examines Fermi’s paradox; However, it is difficult to prove this claim.

Any civilization with a moderate level of rocket technology and colonialist motives could quickly colonize the entire galaxy.

Hart writes in the abstract of his paper: “We see that no intelligent beings from space currently exist on Earth.” This fact can be explained by the hypothesis that there are no other advanced civilizations in our galaxy.” More research into biochemistry, planet formation, and atmospheres is needed to determine the exact answer, he noted.

Hart argued that if intelligent aliens began their interstellar journey more than two million years ago, they likely visited Earth at some point in our planet’s history. The apparent lack of such visitations, he believes, is most likely due to the lack of intelligent aliens. However, Hart offered four other potential explanations:

  • The aliens never got here because of a physical problem that might be related to astronomy, biology, or engineering that makes space travel impossible.
  • The aliens simply chose never to come to us.
  • Advanced extraterrestrial civilizations emerged too late to reach us.
  • Aliens have visited Earth in the past, But we have not seen them.

Frank Tipler, professor of physics at Tulane University, followed Hart’s argument in a 1980 paper titled ” There Is No Extraterrestrial Intelligence.” The bulk of his paper focuses on how to obtain resources for interstellar travel. According to Tipler, interstellar travel can be achieved by having a self-replicating artificial intelligence that creates multiple copies of itself as it moves from one-star system to another.

Because evidence of such advanced intelligence has never been found on Earth, Tipler argues that we are probably the only intelligent beings in the universe. He also wrote in an article in 1980 that those who believe in extraterrestrial intelligence are similar to UFO enthusiasts; Because they both believe that “we will be saved from ourselves by miraculous interstellar intervention.”

Nowadays, extraterrestrial intelligence is a popular topic, and every year numerous articles from different research groups are published about it. The idea that advanced civilizations may exist beyond Earth has been bolstered by the current revolution in the discovery and study of exoplanets.

The abundance of potentially habitable worlds

A view of an exoplanet facing its star

The universe is incredibly vast and ancient. Data collected by various telescopes show that the observable universe is approximately 92 billion light-years across (and growing faster and faster all the time). Also, separate measurements indicate that the universe is nearly 13.82 billion years old. As a result, alien civilizations have had a lot of time to emerge and expand; But before reaching us, they probably have to cross a big cosmic gulf.

When Fermi came up with his famous idea, the only worlds known to scientists were the planets in our solar system. But in 1992, astronomers saw worlds orbiting a superdense stellar body called a pulsar, and a few years later, the first exoplanet was confirmed around a Sun-like star.

Currently, there are more than five thousand confirmed exoplanets and more are being discovered every year. The large number of alien worlds suggests that life may abound throughout the universe.

Read More: 25 surprising facts about the solar system

The large number of alien worlds suggests that life may abound throughout the universe

Now, with advanced instruments like the James Webb Space Telescope, scientists have found it possible to examine the chemical composition of the atmospheres of some nearby exoplanets. However, “adjacent” is a relative term. The nearest known exoplanet, Proxima b, is located at a distance of 4.2 light years from us, which is approximately 40 trillion kilometers.

The ultimate goal is to find out how likely it is to form rocky planets in the “habitable belt” or “habitable zone” of stars. This region is traditionally defined as the range of orbital distances where water can exist on the surface of the world. However, habitability is not just about water, other factors such as the activity of the host star and the composition of the planet’s atmosphere must also be considered. Also, due to some reasons, the habitable area is considered too simple based on the aforementioned definition. For example, icy moons in our own solar system, such as Jupiter’s Europa and Saturn’s Enceladus, lie far beyond the Sun’s habitable zone; But they may still host life in the seas below their surface.

However, it seems that there are many settlements in the world. For example, a November 2013 study using data from NASA’s Kepler space telescope found that one in five Sun-like stars has a roughly Earth-sized planet orbiting it in the habitable zone. A few months later, Kepler scientists announced the discovery of 715 new worlds. Many of these planets were confirmed using a new technique called “multiple proof” that works in part on the logic of probability. For example, objects that pass in front of their star through the telescope or exert gravitational forces on it, are more likely to be planets instead of companion stars; Because with two stars so close to each other, the whole system is likely to become unstable over time.

Artistic rendering of NASA's Kepler Space Telescope

An artist’s rendering of NASA’s Kepler Space Telescope, an exoplanet finder.

However, Sun-like stars are a minority population in our galaxy. Almost three-quarters of the stars in the Milky Way are small, dim flares known as red dwarfs. Astronomers have found several rocky worlds orbiting in the habitable zone of red dwarfs; Like Proxima B and three planets located in Trappist 1; A system that is about 39 light-years away from Earth and contains a total of seven rocky worlds.

However, it is not known how habitable the planets around red dwarfs are; Because these stars are extremely unstable especially when they are young. As a result, their stellar eruptions may quickly destroy the nascent atmospheres of their neighboring planets, making it very difficult for life to flourish. Scientists say more studies are needed to better understand these stars and the ability of life to survive around them.

Researchers are acquiring more tools to study the stars. For example, NASA’s Passing Exoplanet Mapper satellite was successfully launched in April 2018, tasked with discovering extrasolar worlds as a successor to the Kepler telescope. Also, the James Webb Space Telescope, launched in December 2021, will study biological traces in the atmospheres of alien planets, among other tasks. The European Space Agency’s PLATO (Planetary Transit and Stellar Oscillation) spacecraft is also expected to launch in 2026.

Sun-like stars are a minority population in our galaxy

Three massive ground-based observatories, including the Extremely Large Telescope, the Giant Magellan Telescope, and the 30-meter telescope, which is powerful enough to probe the atmospheres of exoplanets, are slated to begin operating by the end of this decade. On the other hand, one of the more ambitious projects known as “Bractro Starshot” wants to study Proxima b and other nearby worlds with an array of tiny laser-guided nanoprobes. If the technology development process goes well, the first such interstellar spacecraft could be launched by around 2050.

These spacecraft and probes will help scientists improve their relatively rudimentary understanding of astrobiology. For example, we still don’t know if there are life-hosting worlds in our cosmic neighborhood. Studies conducted on Earth indicate that microbes can survive in unfavorable environments; A finding that suggests microbial life may exist on Mars, Europa, Enceladus, or Saturn’s giant moon Titan. But we haven’t explored either of those worlds enough to know for sure.

Drake’s equation

Despite the explanations given, Fermi’s paradox paints a much larger picture of microbes. To resolve this paradox, we need to know not only how common life is on alien planets, but also to what extent those extraterrestrials acquire the ability or desire to communicate with other intelligent life forms or to venture among the stars.

The number of intelligent and detectable alien civilizations is estimated by the Drake equation. According to the Seti Institute, the equation is written as “N = R* • fp • ne • fl • fi • fc • L” and has the following variables:

  • N: number of Milky Way civilizations whose electromagnetic emissions can be detected.
  • R*: the rate of formation of stars suitable for the development of intelligent life (number per year).
  • fp: fraction of those stars with planetary systems.
  • ne: the number of planets in each solar system with habitable environments.
  • fl: fraction of suitable planets where life appears.
  • fi: Fraction of life-bearing planets in which intelligent life arises.
  • fc: fraction of civilizations with technologies capable of producing recognizable signs of their existence.
  • L: average length of time such civilizations produce such signs (years).

None of the values ​​of Drake’s equation are currently known with certainty; This means that it is difficult to predict the number of civilizations willing to communicate. As a result, the Fermi paradox is fertile ground for speculation, and scientists and laypeople alike have come up with hundreds of possible explanations over the years.

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Large filter

Asteroid hitting the earth

The large filter is a general idea that attempts to explain Fermi’s paradox. According to this hypothesis, intelligent interstellar life must take many critical steps to evolve, and at least one of these steps must be highly impossible. In fact, the large filter assumes that there is at least one very large barrier that virtually no species can pass to the next stage. But in order to become a truly advanced and space-faring civilization, what important obstacles must be overcome? Here are a few things:

  • A planet capable of harboring life must form in the habitable zone of a star.
  • Life must grow on that planet.
  • Life forms must be able to reproduce using molecules such as DNA or RNA.
  • Simple cells (prokaryotes) must evolve into more complex cells (eukaryotes).
  • Multicellular organisms must grow.
  • Sexual reproduction, which greatly increases genetic diversity, must occur.
  • Complex organisms capable of using tools must evolve.
  • Those beings must develop the advanced technology needed to colonize space. (This stage is roughly where humans are today.)
  • The spacefaring species must continue to colonize other worlds and star systems while avoiding their own destruction.

The assumption of the large filter is that there is at least one very large barrier that virtually no species can pass.

But which stage is the big filter? Unfortunately, no one knows. Maybe the rarity of life is actually a big filter. Maybe life is common, But most organisms do not evolve beyond unicellularity. It may be the great filter of annihilation technology that wipes out its advanced creators. It is possible that an external factor such as the impact of a stray asteroid is the cause of the destruction of life.

If we have passed the great filter, we can hope for our future. Maybe a wise man is the kind that can colonize the world. But if the big filter is still ahead, we’re probably doomed. In the next section, we mention some hypothetical explanations for Fermi’s paradox.

Possible answers to Fermi’s paradox

A very wide range of answers can be considered for Fermi’s paradox. Probably the most obvious and likely answer is that we haven’t looked hard enough for alien life, and interstellar travel is difficult. As mentioned, the first planets beyond the solar system were discovered just 30 years ago; As a result, in the field of exploring alien worlds, we are still in the most elementary stage.

We have yet to find many planets that look exactly like Earth and orbit a Sun-like star. However, even if we were to achieve such success, the distance between the star systems is too great, and travel to them would be extremely difficult. For example, the closest star system to us, Alpha Centauri, is four light years away from Earth. For comparison, the distance from Earth to Neptune is only 0.0005 light years; As a result, it takes tens of years to reach the nearest neighboring star with current technology.

Aliens are not advanced yet

In 2015, scientists analyzing data from the Hubble Space Telescope and the Kepler Space Telescope concluded that Earth was one of the first worlds in the universe to harbor life. According to the researchers, only 8 percent of all potentially habitable worlds that will emerge in the entire lifetime of the universe existed when Earth formed about 4.5 billion years ago. Consequently, this is one possible explanation for the paradox: aliens will come; But not now.

Life is fragile

Perhaps life is too fragile to last long. A 2016 study in the journal Astrobiology showed that the early part of a rocky planet’s history could be very favorable for life; This means that life may usually emerge 500 million years or more after the planet cooled and liquid water became available. Our own Earth history seems to support this conclusion. There is (controversial) evidence that life appeared on Earth about 4.1 billion years ago, and was definitely established by 3.8 billion years ago. But those good days may not last long as a result of the greenhouse effect (as happened on Venus long ago) or other climate changes.

Perhaps life is too fragile to last long

“Between initial heat pulses, freezing, unstable content changes, and out-of-control positive feedbacks, maintaining life on a rocky, wet young planet in the habitable zone is like trying to ride a wild bull,” said Aditya Chopra and Charlie Lineweaver, researchers of the 2016 study. Life often falls.” The authors add that life may be rare in the universe; not because it is difficult to start, but because it is difficult to maintain habitable environments during the first billion years.

Intelligent life destroys itself

Conditions leading to the collapse of life may occur much later. Some thinkers believe that civilizations may self-destruct shortly after they become technologically capable. Again, Earth supports this hypothesis: humanity came alarmingly close to nuclear war during the 1962 Cuban Missile Crisis. Also, we are probably destroying ourselves and many other types of terrestrial life right now through climate change caused by our own activities or the development of dangerous technologies such as artificial intelligence.

Other Answers

There are many other factors to consider. For example, Alan Stern, a planetary scientist and director of NASA’s New Horizons mission, believes that buried oceans, such as the seas of Enceladus and Europa, are likely the most common environments for life in the Milky Way. As a result, it seems unlikely that the evolved beings in such regions would achieve the necessary technology to build spacecraft. In fact, many of them may not even know that there are other worlds to explore.

Alien psychology can also be effective. For example, maybe there are many advanced alien civilizations in the world; But most of them don’t want to communicate with us or visit Earth. Perhaps Earth and its inhabitants are simply not interesting enough for aliens to waste their time on, and until humanity shows enough intelligence and competence to be accepted into the “galactic club”, it will not attract the attention of extraterrestrials.

Most intelligent aliens may tend to be silent as a general rule; Because they are worried that contact with their cosmic neighbors will lead them to slavery or death. Some researchers, including the late Stephen Hawking, have cited such possibilities with the argument that humans should not actively show their presence.

Most intelligent aliens may tend to be silent as a general rule

In addition to all the aforementioned assumptions, finding intelligent aliens in a very, very vast and ancient universe is associated with complex logistical problems. Mankind only appeared on Earth 200,000 years ago and only started listening to possible radio signals from extraterrestrials in 1960. As a result, the probability that it overlaps with a recognizable alien civilization in terms of time and place does not seem very high.

Most researchers say that there is probably no single solution to Fermi’s paradox. A combination of factors, including perhaps some of the ones discussed above, is probably responsible for the great silence that currently reigns in the world. The nature of those factors will probably be more clearly noticed relatively soon.

For example, suppose scientists find evidence of ancient or current microbial life on Mars, Europa, or any other body in our own solar system. The discovery of such creatures near the Earth, which are completely different from terrestrial life, speaks of the “Second Genesis” and definitely shows the commonness of life throughout the universe. At that point, researchers can cross off a possible explanation on the long list of explanations for Fermi’s paradox. 

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How did photographing “nothing” change astronomy?




How did photographing "nothing" change astronomy?
In deep-field photography, the empty and dark part of the sky is chosen to photograph faint galaxies in the distance. The Deep Webb Space Telescope and other telescope images from these regions are more fruitful than we imagine. So how did photographing “nothing” change astronomy?

How did photographing “nothing” change astronomy?

On July 11, the world was stunned by the release of the deepest astronomical image ever recorded by the James Webb Space Telescope ( JWST ). In the background of the galaxy cluster called SMACS 0723, whose image is from 4.6 billion years ago, thousands of galaxies of different shapes and sizes shine like brilliant diamonds in the dark universe. Some of these distant beacons were shining when the universe was only a few hundred million years old. Understanding the path of this achievement, including reaching distant cosmic islands and collecting photons that began their journey near the Big Bang, will help better understand observations of the deep field.

The origin of the first James Webb Deep Space Telescope wallpaper dates back to the early 1990s and the launch of the Hubble Space Telescope. At that time, the deep field observation project was still in its infancy. Hubble was originally designed for targeted observations, and astronomers were supposed to use this telescope to observe a specific part of the sky based on the brightness of the light source; But Hubble also had the ability to photograph the deep field, which was exactly in front of the goal of astronomers: for this type of observation, astronomers place the telescope towards a region of the sky that does not have any visible light source, and from a very long exposure time to reach the depths of the universe and They use observation of dim light sources. At that time, Hubble was the best instrument for deep-field imaging.

Read More: 25 surprising facts about the solar system

However, not everyone agreed with the observation of the deep field. In a 1990 paper in the journal Science, John Bahcal and his colleagues from the Institute for Advanced Study point out that Hubble’s deep background image does not show many more galaxies than ground-based telescopes. Bahcal is best known for his solution to the solar neutrino problem and his calculations of the distribution of stars around a supermassive black hole. He was instrumental in the development of the Hubble telescope from its original design in the 1970s to its launch. Bahkal believed that Hubble’s deep field would not reveal new populations of galaxies, but such images could provide confirmation of the morphology and size of faint galaxies and the statistics of quasars.

Hubble and James Webb Deep Wallpaper Comparison

Comparison of the first Hubble Space Telescope “deep field” image captured in 1995 (left) and the first similar image from the James Webb Space Telescope (right). Both images cover roughly the same area of ​​the sky but contain different populations of galaxies. The Webb Telescope, for example, covers more cosmic time and reveals galaxies older than the early universe.

Such expectations suppressed the need for deep-field imaging with Hubble. For this reason, the first attempt to photograph the deep field was made around the winter holidays of 1995 after the optical repair of the telescope. The telescope took 10 days of exposure time for a small part of the sky in the constellation Ursa Major. After weeks, astronomers got their Christmas present by seeing the final image known as the Deep North Field.

The number of stars in the Milky Way galaxy was very small in the target area, so the Hubble telescope looked into the depths of the universe, just like a viewer looking into a pinhole. This telescope observed nearly 3,000 faint galaxies of various shapes and sizes, some of which were 12 billion light-years away from Earth. Hubble’s mission was not only to explore space but also to study time and collect light from stars that existed billions of years ago in the early cosmic ages. The Hubble Deep wallpaper quickly became an iconic image.

But a fundamental question was raised: was the galaxy-filled region in the deep field north image normal? Or were the astronomers lucky enough to point the telescope at a point full of galaxies? In 1998, the Hubble telescope captured the southern image of the deep field. The exposure of this photo was similar to the previous one, with the difference that this time the telescope was facing the southern hemisphere of the sky, which is at the farthest possible distance from the first point. The new image proves that the universe is more galaxy-filled than previously thought, especially in the far reaches. In addition to scientific value, Hubble’s deep fields revealed a technical challenge; These images covered more than 10,000 galaxies, which was the first big data challenge for astronomers.

Hubble and James Webb telescopes

The Hubble Space Telescope as seen from the space shuttle in low Earth orbit (top) James Webb Space Telescope imaging (bottom) at a distance of more than 1.5 million kilometers from Earth.

Deep-field imaging is not limited to the visible spectrum. By the beginning of the third millennium, the universe was preparing for the first deep, energetic image from the Chandra X-ray telescope. NASA’s revolutionary telescope was launched in July 1999 and has continued to operate until today. Chandra’s deep-field south image was captured with an exposure time of approximately one-millionth of a second over a portion of the sky in the Lockman Hole, a window of hydrogen clouds and dust in the Milky Way. An image south of Chandra’s deep background revealed a strange universe: hundreds of black holes that some placed far away. Although this image was not as eye-catching as the Hubble images, it contained a lot of scientific information. This field was re-imaged by Chandra with a total exposure of seven million seconds, yielding the deepest field in the X-ray spectrum. In 2003, the Chandra Deep North Image was released, which included more than 500 X-ray sources.

With the addition of instruments such as the Advanced Mapping Camera to Hubble, the Hubble Deep Space Wallpaper was released in 2006. This historic image included thousands of galaxies, and some of them were less than a billion years old. The ultra-deep field provided unprecedented details of the formation history of galaxies; Distant galaxies appeared smaller and more irregular than closer galaxies, and this observation became a support for theories of galactic evolution.

The ultra-deep field is the deepest image that can be captured at visible wavelengths. If a galaxy is too far away, its visible light is transferred out of the visible spectrum and into the infrared spectrum; This phenomenon is the result of the cosmic redshift effect, according to which the expansion of the universe causes the length of light wavelengths to be stretched, which travel huge intergalactic distances.

With this account, the infrared camera was necessary to observe longer distances in space and time. With the addition of the near-infrared camera to the Hubble telescope, the field of far-infrared was released in 2009; This image revealed galaxies that were glowing just 600 million years after the Big Bang. A decade later in 2019, another deep field was released by NASA’s Spitz Infrared Space Telescope. Both images had fruitful results for the discovery of galaxies on a cosmic scale.

Finally, Hubble’s Frontier Fields campaign provided a new deep-field imaging capability that became the precursor to James Webb’s first deep-field image. During the observing campaign, which ended in 2017, Hubble aimed at six major galaxy clusters. According to Einstein’s theory of general relativity, mass density can bend along the path of light and thus amplify the light received from the background source with an effect called gravitational lensing; Therefore, these galaxy clusters were used as microscopes for distant observations.

In addition to galaxy-filled images, Frontier Fields images contain strange arcs of light that show enhanced or stretched images of background galaxies much farther from the cluster. These galaxies are so faint that it is not possible to directly observe them with Hubble. These images show some of the most distant galaxies and the first supernova transformed into a gravitational lens.

Almost 200 years have passed since the advent of photography. At that time, for the first time, humans were able to trap photons to record images. Today, highly sophisticated cameras on space telescopes millions of kilometers beyond the Earth push the boundaries of our knowledge of the universe and open new windows to space and time. There is a relatively short period of time between these two inventions, but both were designed with the same goal: to gain an understanding of nature by looking at what is not visible to the human eye.

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25 surprising facts about the solar system




25 surprising facts about the solar system

From the vastness of the solar system and its strange moons to the ubiquitous presence of water and organic molecules, our solar neighborhood is full of surprising facts.

25 surprising facts about the solar system

Our solar system includes the sun and everything that revolves around it; Among the eight planets that we have all been familiar with since elementary school. But the main planets, despite their diversity and charm, are only part of the wonders of our cosmic neighborhood. Planet Earth’s neighbors in space include comets, asteroids, dwarf planets, mysterious moons, and a series of phenomena so strange and alien that they are not easily explained.

Table of Contents

  • 1. The solar system is very, very large
  • 2. Even our neighborhood is very big
  • 3. Uranus orbits the Sun sideways
  • 4. Jupiter’s moon Io is full of volcanic eruptions
  • 5. Mars has a volcano that is bigger than the entire state of Hawaii
  • 6. The biggest canyon on Mars could take Earth’s Grand Canyon in one bite
  • 7. Venus is swept by super-powerful winds
  • 8. Water is everywhere
  • 9. Human spacecraft have visited all planets
  • 10. Pollutants may be transported to habitable areas
  • 11. Mercury is shrinking
  • 12. Pluto has mountains
  • 13. Pluto has a strange atmosphere
  • 14. Rings are more common than you might think
  • 15. Jupiter’s Great Red Spot is shrinking
  • 16. Most comets are detected with solar telescopes
  • 17. The ninth planet
  • 18. Neptune is very hot
  • 19. Earth’s Van Allen Belt is much stranger than expected
  • 20. What happened to Miranda?
  • 21. Saturn’s yin-yang moon
  • 22. Titan has a liquid cycle, But there is no water involved
  • 23. Organic molecules are everywhere
  • 24. Saturn has a hexagonal storm
  • 25. The atmosphere of the Sun is much hotter than the surface of the Sun

From fascinating glaciers on the dwarf planet Pluto and a deep valley the size of the United States on the Red Planet to the possibility of a giant, undiscovered world known as the ninth planet beyond Neptune, the space around Earth is full of wonders. Stay tuned to Zoomit for some of the weirdest facts about the solar system.

25 surprising facts about the solar system

1. The solar system is extremely largeOort cloud and Kuiper belt

By including the Oort cloud, our star’s realm becomes much, much larger.

NASA’s Voyager 1 spacecraft began its mission in 1977, and more than three decades later in 2012, it became the first man-made object to enter interstellar space by passing through the heliopause or heliosphere boundary. The heliopause is the region where the magnetic fields and most of the particles emitted from the sun disappear.

However, according to NASA, “If we define our solar system as the Sun and primarily everything that orbits it, Voyager 1 will continue to remain within [dominance of] the Sun until, in the next 14,000 to 28,000 years, Get out of the Everett cloud. 

2. Even our neighborhood is very big

Visualization of the placement of all the planets of the solar system between the Earth and the Moon

Did you know that all the planets in the solar system can fit between the Earth and the Moon?

Depending on how accurately you do the math and how you arrange it, all the planets in the solar system can fit between the Earth and the Moon. The distance between the Earth and the Moon varies as does the diameter of each of them. Our planet and its moon are wider at their equator; As a result, Saturn or Jupiter or both must be slightly tilted to the sides to fit between them. However, if you lined up the planets from pole to pole, they would barely fit between us and our only space companion, blocking the sky with their rings and huge gas masses.

The moon is the farthest object humans have ever traveled to, and depending on how you think about it, it’s both amazingly far and incredibly close. Eight giant planets of the solar system can fit in the space between us and the moon, and yet, the distance from the Earth to the sun is more than 390 times the distance from the Earth to the moon.

Scientists use the approximate distance from the Earth to the Sun, known as an astronomical unit, or AU, to compare distances within the solar system. Jupiter is approximately 5.2 AU from the Sun and Neptune is 30.07 AU or approximately 30 times the distance from Earth to the Sun from our star.

 3. Uranus orbits the sun sideways

Composite image of the planet Uranus and its rings

This composite image of the two hemispheres of Uranus was obtained with the adaptive optics of the Keck telescope. The north pole of the planet is at 4 o’clock.

In solar system models, Uranus usually appears as a blue ball with no special features; But this gas giant, located in the outer limits of the solar system, is very strange from a global perspective. First of all, the seventh planet of the solar system has a very extreme axial deviation of 97.77 degrees; This means that it rotates sideways and completes its orbit around the sun like a rolling ball. The most likely explanation for the planet’s unusual orientation is a catastrophic collision with another body in the distant past.

The tilt of Uranus has caused NASA to witness the most unusual seasons in the solar system on this planet. In about a quarter of each Uranian year (equivalent to 21 Earth years), the Sun shines directly on the north or south pole of the planet; This situation means that half of Uranus does not see the Sun at all for more than two Earth decades.

Scientists have been monitoring these temperate seasons on Uranus and predicting that they will witness unusual weather on this planet at the moment of the 2007 equinox. But it was seven years later that unexpected violent storms occurred in the atmosphere of Uranus, and the planet became a bigger mystery than ever. 

4. Jupitor’s moon Io is full of volcanic eruptions

The eruption of the volcano in Io from the view of the Galileo spacecraft

Io has hundreds of active volcanoes. In this image, the moment of the spectacular eruption was captured by NASA’s Galileo spacecraft as it flew over the moon.

Jupiter’s moon Io may seem like a world of surprise compared to Earth’s silent moon. This Galilean moon, which is slightly smaller than the Earth’s moon, has hundreds of volcanoes and is considered the most active moon in the solar system. Io sends masses of sulfur smoke up to 300 km into its atmosphere. According to NASA, Io’s volcanoes emit a ton of gas and particles every second into space near Jupiter.

The eruptive nature of Io is due to the enormous forces that this moon is exposed to. Trapped in Jupiter’s gravitational well and magnetic field, Io experiences constant tension and relaxation as it moves away from the planet and approaches it, gaining enough energy for volcanic activity.

Scientists are still trying to figure out how heat is distributed inside Io. However, it is difficult to predict the location of volcanoes using only scientific models. 

5. Mars has a volcano that is bigger than the entire state of Hawaii

Mount Olympus on Mars

Mount Olympus is the largest volcano discovered in the solar system.

Although Mars seems peaceful now, giant volcanoes once ruled the planet’s surface. One of these volcanoes is Mount Olympus, the largest volcano discovered in the solar system. With a width of 602 km, Olympus can be compared to the state of Arizona in America. The height of this volcano is 25 km or three times higher than Everest, the highest mountain on earth. According to NASA, Olympus is 100 times larger in volume than Mauna Loa, the largest volcano on Earth in Hawaii.

Scientists suspect that volcanoes can grow to such enormous sizes on Mars because of Mars’ weak gravity compared to Earth’s. Moreover, while the earth’s crust is constantly moving, the crust of Mars is probably stationary based on the belief of some researchers. If the surface of Mars does not move, a volcano can form in one spot for a longer period of time. 

25 surprising facts about the solar system

6. The biggest canyon on Mars could take Earth’s Grand Canyon in one bite

Mariner Valley on Mars

Mariner Canyon on Mars is more than 10 times longer than the Grand Canyon on Earth.

The huge system of Martian canyons, known as the Mariner Canyon, is 4,000 kilometers long, more than 10 times larger than the Grand Canyon on Earth. Mariner Canyon was overlooked by early Martian spacecraft that flew over other parts of the planet and was finally discovered by the Mariner 9 probe in 1971. If the Mariner Valley was located on Earth, it could stretch from the East Coast to the West Coast of America.

The lack of active plate tectonics on Mars makes it difficult to discern how Mariner Valley formed. Some scientists think that a chain of volcanoes on the other side of the planet, known as the Tharsis Plateau, which includes Mount Olympus, somehow bent the crust away from Mars. That destructive force created fissures in the crust, exposed vast amounts of groundwater to excavate the rocks, and formed glaciers that opened new routes into the canyon system. 

7. Venus is swept by super-powerful winds

Computer image of the rocky surface of the planet Venus

This artistic image shows the rocky surface of Venus and sulfuric acid clouds.

Venus is a hellish planet with a high temperature and pressure environment on its surface. The second planet in the solar system is extremely dry and hot enough to melt lead and has probably never had an environment conducive to supporting life. When the heavily protected Venus spacecraft from the Soviet Union landed on Venus in the 1970s, each lasted only a few minutes, or hours at most, before melting or shattering.

However, Earth’s infernal twin has a far stranger environment beyond its surface. Scientists have found that the winds in the upper atmosphere of Venus blow 50 times faster than the rotation of the planet. The European Venus Express spacecraft, which orbited Venus between 2006 and 2014, tracked the winds over long periods and detected periodic changes. The probe also showed that powerful winds appear to be getting stronger with time.

A study in 2020 pointed to the presence of phosphine, which is a possible sign of the decay of biological materials, in the clouds of Venus. This study initially excited some astrobiologists, But the supplementary research firmly rejected the possibility of the existence of life in the dry and windy atmosphere of Venus. 

8. Water is everywhere

Computer image of Mars with water lakes

This artistic rendering shows what Mars would look like with water lakes.

At one time, water was considered as a rare substance in space; But the truth is that water ice exists throughout the solar system and is a common constituent of comets and asteroids.

Water can be found as ice in the permanently shadowed craters of Mercury and the Moon. However, we don’t know if there is enough water to support possible human settlements in those places. Also, Mars has ice on its poles. Even smaller solar system objects, such as Enceladus, Saturn’s moon, and the dwarf planet Ceres, have ice.

NASA scientists believe that Jupiter’s moon Europa is the most likely candidate known to support extraterrestrial life; Because contrary to all expectations, liquid water is probably flowing under its cracked and frozen surface. Europa, which is much smaller than Earth, probably has a deep ocean that researchers believe contains twice as much water as all the oceans on Earth combined.

However, we know that not all ice is the same. For example, a close examination of comet 67P/Churyumov-Grasimenko by the European Space Agency’s Rosetta spacecraft revealed a different type of water ice than that found on Earth. 

9. Human spacecraft have visited all planets

Montage of Voyager 2 images of the outer planets of the solar system

The outer planets of the solar system as seen by the Voyager 2 spacecraft.

We’ve been exploring space for over 60 years and have been lucky enough to get close-up images of dozens of celestial bodies. Most importantly, we have sent spacecraft to all the planets in the solar system, including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, as well as the two dwarf planets, Pluto and Ceres.

Most of the close flybys of the planets were made by NASA’s Voyager twins, which left Earth more than four decades ago and are still transmitting data from interstellar space to this day. Voyagers met all of them during their long journey, thanks to a rare alignment of the outer planets. 

10. Pollutants may be transported to habitable areas

Hydrothermal vents on the ocean floor

Hydrothermal vents in the ocean.

Scientists have not yet found evidence of life in other parts of the solar system; But as they learn more about the hardy microbes that inhabit Earth’s harsh environments, such as ocean-floor hydrothermal vents or frozen environments, they have more opportunities to find alien life on other planets.

Currently, the presence of microbial life on Mars is considered so probable that scientists take special precautions to clean spacecraft bound for this planet. NASA decided to crash the Galileo spacecraft into Jupiter to avoid the risk of contaminating Europa’s potentially habitable oceans. 

Read More: Will Earth one day become a wandering planet?

25 surprising facts about the solar system

11. Mercury is shrinking


Mercury, the smallest planet in our solar system, has short years, long days, and extreme temperatures.

With the exception of the dwarf planet Pluto, Mercury is currently the smallest planet in the solar system and the most dense planet after Earth. However, the innermost planet in our solar neighborhood is shrinking and becoming denser.

For many years, scientists believed that Earth was the only tectonically active planet in the solar system. But after NASA’s MESSENGER spacecraft, performing its first orbital mission on Mercury, mapped the entire planet in high resolution and took a look at its surface features, this belief changed.

In 2016, MESSENGER data revealed chasm-like features known as fault chasms. Because these fault chasms are relatively small, scientists are confident that they did not form long ago and that Mercury is still contracting, 4.5 billion years after the formation of the solar system. 

12. Pluto has mountains

Pluto's mountains as seen by the New Horizons spacecraft

In July 2015, NASA’s New Horizons spacecraft sent back impressive images of Pluto and its moons.

Pluto is a small world at the edge of the solar system; As a result, scientists thought that this dwarf planet would have a completely uniform environment full of craters. But this belief changed in 2015. That year, NASA’s New Horizons spacecraft flew past Pluto and sent back unprecedented images, forever changing the way we look at this distant object.

Among the amazing discoveries of New Horizons, there were icebergs with a height of 3,300 meters; A finding that suggests Pluto must have been geologically active at least 100 million years ago. But geological activity requires energy, and the source of this energy inside Pluto is a mystery. The Sun is too far away to generate enough heat for geological activity, and there are no large planets close enough to Pluto to cause such a gravitational disturbance. 

13. Pluto has a strange atmosphere

Pluto's atmosphere as seen by the New Horizons spacecraft

NASA’s New Horizons spacecraft took this image of Pluto from a distance of 200,000 km. Pluto’s atmosphere can be seen as a blue haze.

Pluto’s observed atmosphere disproved all predictions. The scientists observed that the dwarf planet’s unexpectedly hazy atmosphere extends up to 1,600 km and extends beyond the Earth’s atmosphere, away from the surface. When data from NASA’s New Horizons mission came in, scientists began analyzing the nebula and discovered some surprises there as well.

Scientists have found nearly 20 layers in Pluto’s atmosphere that are both colder and denser than expected. This feature affects calculations related to the rate of loss of Pluto’s nitrogen-rich atmosphere in space. The New Horizons team found that thousands of kilograms of nitrogen gas escape from the dwarf planet every hour; But Pluto somehow manages to continuously replenish the lost nitrogen. The recovery of this gas is probably done mostly through geological activities. 

14. Rings are more common than you might think


Saturn is not the only ringed object in the solar system.

Since the invention of telescopes in the 17th century, we have known about the existence of rings around Saturn; But to reveal more rings, we needed the powerful spacecraft and telescopes built in the last 50 years. We now know that all the outer planets of the solar system, including Jupiter, Saturn, Uranus, and Neptune, have ring systems.

However, the rings vary from planet to planet: Saturn’s spectacular ring, which is partly made of glowing, reflective water ice, is unmatched anywhere else. In contrast, the rings of other giants are probably made of rocky particles and dust.

Rings are also not limited to planets. For example, in 2014 astronomers discovered rings around the asteroid Chariklo. 

15. Jupiter’s Great Red Spot is shrinking

The Great Red Spot of Jupiter

Jupiter’s Great Red Spot is the largest storm in the solar system.

Besides being the largest planet in the solar system, Jupiter also hosts the largest storm in the solar neighborhood. This red storm, known as the Great Red Spot, has been observed in telescopes since the 17th century and studied with modern instruments such as NASA’s Juno probe. The spacecraft has recently provided evidence that Jupiter’s giant storm is hundreds of kilometers high and is likely fed by winds thousands of kilometers below. This storm has been a complex mystery for centuries; But in recent decades, another secret has been revealed: the Great Red Spot is shrinking.

In 2014, Jupiter’s Great Storm was only 16,500 km wide, roughly half its historical size. This diminution is monitored by professional telescopes as well as amateur astronomers. Amateurs can often take more consistent measurements of the client; Because the observation time in larger and professional telescopes is limited and is often divided between different objects. 

25 surprising facts about the solar system

16. Most comets are detected with solar telescopes

Comet Ison

Comet Ison appears from the lower right of the image and moves to the upper right. This impressive image was captured by the Horspeary Solar Observatory, and the image of the Sun in the center was obtained from NASA’s Solar Dynamics Observatory.

Comets used to be the domain of amateur astronomers who probed the sky night after night with their telescopes. Although some professional observatories also made discoveries while observing comets, the status of explorations in this field started to change with the launch of the Solar and Horseshoe Observatory (SOHO) in 1995.

Since then, SOHO has found more than 2,400 comets. This volume of comet discovery has been a very fruitful side mission for a probe that only observes the Sun. The nickname of these comets is “Sunriser” or “Solstice”. Many amateur astronomers continue to help find these objects by identifying comets in raw SOHO images. One of SOHO’s most famous observations was when it observed the collapse of the bright comet Ison in 2013. 

17. The ninth planet

Hypothetical ninth planet

A ninth planet is a hypothetical world that could explain the motion of some Kuiper belt objects.

In January 2015, California Institute of Technology (Caltech) astronomers Konstantin Batygin and Mike Brown, relying on calculations and mathematical simulations, announced that a giant planet might be hidden far beyond Neptune. Now several teams are searching for this hypothetical “ninth planet” and research shows that it is possible to discover it within the next decade.

A ninth planet, if present, could help explain the motions of some objects in the Kuiper Belt (an icy collection of objects beyond Neptune’s orbit). Brown has already discovered several large bodies in that region, in some cases rivaling Pluto in size. In fact, his discoveries were the catalyst for Pluto’s status change from a planet to a dwarf planet in 2006.

But some scientists follow another theory; That “Planet Nine” might actually be a black hole the size of Grapefruit that bends space just like a giant planet. However, another team suggests that the strange movements of the Kuiper belt’s distant inhabitants are likely the collective effect of several small objects; No undiscovered planets or black holes. 

18. Neptune is very hot

The planet Neptune from the perspective of Voyager 2

The distance of Neptune from the Sun is approximately 30 AU.

Neptune, the outermost planet in the Solar System, is 30 times farther from the Sun than Earth and receives less light and heat. However, Neptune emits much more heat than it receives and has a much more active atmosphere than its neighbor Uranus. Uranus is closer to the Sun, yet emits nearly as much heat as Neptune. Scientists still do not know the cause of this problem.

The wind on Neptune can blow up to 2400 km/h. Does this amount of energy come from the sun, the planet’s core, or gravitational contraction? Researchers are trying to find the answer to this mystery. 

19. Earth’s Van Allen Belt is much stranger than expected

Van Allen belts around the earth

Discovered in 1958, the Van Allen belts are large bands of radiation that surround the Earth and expand and contract based on the activity of the Sun.

The Earth has several magnetically trapped bands of highly energetic charged particles around it, called the Van Allen Belts in honor of their discoverer. Although we’ve known about these belts since the dawn of the space age, the Van Allen probes, launched in 2012, provided the best possible picture of them and revealed many surprises along the way.

We now know that the belts expand and contract based on the activity of the sun. Sometimes the belts are very distinct from each other, and at other times, they swell as one large unit. An additional radiation belt, beyond the two known, was discovered in 2013. Understanding these belts helps scientists make better predictions about space weather or solar storms. 

20. What happened to Miranda?

Miranda, the moon of Uranus

Uranus’ moon Miranda has one of the most diverse landscapes of any extraterrestrial object.

One of the strangest outer moons of the solar system is Miranda. This mysterious moon of Uranus was observed only once in 1986; Voyager 2 caught a glimpse of it during its tour of the solar system. Miranda hosts sharp ridges, craters, and other large discontinuities on its surface that are usually the result of volcanic activity. Tectonic activity can cause the formation of such a surface, But Miranda is too small to generate that kind of heat on her own.

Researchers believe that the gravitational pull of Uranus could have caused the necessary pressure to heat, overturn, and deform Miranda’s surface. But to be sure, we need to send another spacecraft to investigate the unseen northern hemisphere of the moon. 

25 surprising facts about the solar system

21. Saturn’s yin-yang moon

Iaptus, a moon of SaturnIaptus, a moon of Saturn

Saturn’s moon Iapetus shows drastic differences in surface brightness depending on which side it faces the Sun.

Saturn’s moon Iaptus has a very dark hemisphere that always faces the planet and a very bright hemisphere that always faces Saturn. The brightness of most asteroids, moons, and planets is relatively uniform across their surfaces; But Iaptus sometimes shines so brightly that it was observed by the Giovanni Cassini telescope in the 17th century, and then dims considerably as it spins the other way.

Current research shows that Iaptus, also known as Saturn 8, is made mostly of water ice. According to scientists’ hypothesis, when the dark side of the moon faces the sun, water ice sublimates from that area and leaves behind darker rocks. Since dark matter heats up more than bright, reflective ice, this process may have created a positive feedback loop; In this way, when the darker and warmer part of the moon loses its ice, it heats up more easily when facing the sun and accelerates the loss of ice. 

22. Titan has a liquid cycle, But there is definitely no water involved

Artistic rendering of Titan's lakes

Titan’s lakes are full of methane and ethane and possibly a layer of water.

Another strange moon of the solar system is Titan, a moon of Saturn. Titan hosts a “fluid cycle” that moves material between the atmosphere and the surface. This circulation of materials is apparently very similar to the water cycle on Earth; But Titan’s huge lakes are filled with methane and ethane, probably on top of a layer of water.

Using data from the international Cassini mission, researchers hope to uncover some of the moon’s secrets before designing a submarine that could one day explore Titan’s mysterious depths. 

23. Organic molecules are everywhere

The rough surface of comet 67P/Churyumov-Grasimenko

Organic molecules have been found in many places in the solar system, including comet 67P/Churyomov-Grasimenko. In this image, the rugged landscape of the comet’s core was captured by the Rosetta spacecraft.

Organics are complex carbon-based molecules found in living organisms, But abiotic processes can also be their creators. Although common on Earth, organic molecules can be found unexpectedly in many other places in the solar system. For example, scientists have discovered organic matter on the surface of comet 67pi. The hypothesis that organic molecules were probably brought to the surface of our planet from space to start life on Earth was strengthened by the discovery of these molecules in comet P67.

Organic matter has also been found on the surface of Mercury, Titan, Saturn’s moon (which gives it its orange color), and Mars. 

24. Saturn has a hexagonal storm

Saturn's strange hexagonal storm

Saturn’s northern hemisphere is home to a strange hexagonal storm that has been raging for decades.

Saturn’s northern hemisphere has an intense six-sided storm known as the “hexagon”. This hexagon, a towering multi-layered storm, has existed for decades, perhaps even hundreds of years.

Saturn’s strange storm was discovered in the 1980s; But until the Cassini spacecraft flew between 2004 and 2017, it was difficult to observe it. Cassini images and data showed that the hexagonal storm is 300 km high and 32 thousand km wide and consists of air moving at a speed of 320 km/h. 

25. The atmosphere of the Sun is much hotter than the surface of the Sun


The temperature of the sun is different in each layer of its atmosphere.

While the temperature of the visible surface of the sun or photosphere is 5500 degrees Celsius, the temperature of the upper atmosphere or corona (solar corona) reaches millions of degrees. This extreme temperature difference is one of the great mysteries of the star of our system.

However, NASA has several solar-observing spacecraft in its fleet of probes, and they have some hypotheses for how heat is generated in the sun. One such idea is the “heat bombs” that occur when magnetic fields align in the corona. Another hypothesis is related to the time when plasma waves move from the surface of the Sun to the corona.

With new data from the Parker probe, which has become the closest man-made object to the Sun,we are closer than ever to unlocking the secrets of the heart of the Solar System.

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