Although the universe contains billions of galaxies, and each galaxy contains billions of stars, our own solar system can still be very interesting. It includes one star, eight planets, at least five dwarf planets, over 100 moons, thousands of known comets, and countless asteroids. Although the solar system is usually shown with the planets very close together, they are actually extremely far apart.
The Sun
The Sun is the star at the center of our solar system. It is a medium-sized star, meaning that it will not end in a supernova. Right now, the Sun is about five billion years old; in another five billion years, it will expand to 100 times its size and become a red giant, before its outer layers float off and become a nebula, leaving the Sun's core as an Earth-sized star known as a white dwarf. The Sun currently has a diameter of 864,340 miles (1,391,000 km), and a mass of almost two sextillion megatons, or 333,000 times the mass of Earth. Its surface is about 10,000 degrees Fahrenheit (5,500 degrees Celsius). The Sun is one AU from Earth, 8.3 light-minutes, or 92.9 million miles (149,500,000 km). Although the warmth from the Sun allows there to be life on Earth, it can also be very dangerous. Heat can be trapped on Earth by greenhouse gases, increasing temperatures on Earth. The Sun also emits harmful ultraviolet rays. Most of these ultraviolet rays are blocked by the ozone layer, although they can still cause sunburns.
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Mercury
Mercury is the innermost planet in the solar system. It is also the smallest planet, with a diameter of about 3,032 miles (4,879 km). Mercury's surface gravity is only 3.7 m/s², meaning that a person who weighs 100 pounds on Earth would only weigh 38 pounds on Mercury. A year on Mercury lasts only 88 Earth days, but a day on Mercury lasts 59 Earth days because of Mercury's slow rotation. Due to Mercury's extremely thin atmosphere, and the fact that it orbits at a distance of only 0.38 AU (35.3 million miles or 56.8 million km), temperatures on Mercury's surface vary greatly. On the side of Mercury that is not exposed to the Sun, temperatures can be as low as -261 °F (-162 °C). However, on the side of Mercury that is exposed to the Sun, temperatures can reach 800 °F (426 °C). Because Mercury's atmosphere is almost nonexistent, it is covered in craters. The largest crater on Mercury, the Caloris Basin, has a diameter of 963 miles (1,550 km). MESSENGER, which was launched in 2004, has discovered evidence of volcanoes on Mercury's surface.
GREEK: Named after Hermes |
Venus
Venus is the second closest planet to the Sun. It orbits at a distance of about 0.72 AU, or 67.2 million miles (108,100,000 km). A day on Venus lasts 116 Earth days, and Venus rotates in the opposite direction of the other planets; this means that the Sun rises in the west and sets in the east. A year on Venus lasts 224 Earth days. Venus is the most similar in size to Earth, with a diameter of 7,521 miles (12,103 km). Venus is also the hottest of the planets, with a surface temperature of 864 °F (462 °C). Venus's atmosphere is composed almost completely out of carbon dioxide, with no breathable oxygen. Venus's atmosphere is also 90 times as dense as the atmosphere on Earth, meaning it would crush anyone who went there. The clouds that cover Venus are made of sulfuric acid instead of water vapor, which clouds on Earth are made of. At the top of Venus's clouds, there are also winds moving at 185 mph (298 kph). Venus used to be very similar to Earth, but was later turned into its current form by the greenhouse effect, due to the massive amounts of carbon dioxide in its atmosphere.
GREEK: Named after Aphrodite |
Earth
Earth is the third planet in the solar system, and the only planet known to support life. It orbits the Sun at a distance of 92,960,000 miles (149.6 million km), or exactly one AU. Earth has a diameter of 7,918 miles (12,742 km) and a mass of 5.97 quadrillion megatons (5,970 yottagrams). Earth has one moon that orbits it at a distance of 238,900 miles (384,400 km) and has a diameter of 2,159 miles (3,474 km). Earth's has many volcanoes and has seismic activity, including earthquakes. About 71% of Earth is covered in water, while the rest is land. These oceans can reach as deep 6.83 miles (10.99 km) at the bottom of the Mariana Trench. Earth's surface has an average temperature of 58.3 °F (14.61 °C), but temperatures as high as 136 °F (57.78 °C) and as low as -128 °F (-89.22 °C) have been recorded. Earth's atmosphere is 78% nitrogen, 21% oxygen, 1% argon, and small amounts of other gases such as carbon dioxide and water vapor. See the Environment pages for more information about our home planet!
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Mars
Mars is the fourth planet from the Sun. It has a diameter of 4,212.2 miles (6,779 km), which is about 53% of Earth's diameter. It orbits the Sun at a distance of 141,634,900 miles (227.9 million km), or about 1.52 AU. With an orbital eccentricity of about 0.09, Mars has the second most eccentric (or least round) orbit in the solar system, second only to Mercury. There are large amounts of frozen water on Mars, especially within Utopia, a crater with a diameter of about 2,051 miles (3,301 km). The amount of frozen water in this area was estimated to be the same amount of water as in Lake Superior on Earth. The tallest mountain in the solar system, Olympus Mons, which is 13.6 miles (22 km) tall, compared to only about 5.5 miles (8.85 km) from Mount Everest on Earth. Mars has two very small moons, Phobos and Deimos. Phobos has a diameter of almost exactly 7 miles (11.27 km) and orbits mars at a distance of only 5,825 miles (9,374 km). Phobos gets closer to Mars every year, and it is estimated that it will collide with Mars in the next 50 million years. Deimos orbits much farther away, at a distance of 14,691 miles (23,643 km), and is only 56% the size of Phobos. Gravity on Phobos is so weak that someone who weighs 100 pounds on Earth would weigh less than half an ounce on Phobos. Mars itself also has the largest canyon in the solar system: Valles Marineris, which is over 2,500 miles (4,000 km) long and over four miles (6.44 km) deep in some places.
GREEK: Named after Ares |
The Asteroid Belt
Between the orbits of Mars and Jupiter, at a distance of between 2.2 and 3.2 AU (204 million to 298 million miles or 329 million to 488 million km) from the Sun. Within the asteroid belt, there are over 1,700,000 asteroids with a diameter of over one kilometer (0.62 miles). The largest asteroid in the asteroid belt is Ceres, with a diameter of about 590 miles (950), which is so large that it is considered a dwarf planet. Most asteroids are very small, with some the size of specks of dust. The asteroids are actually so spread out that the odds of a probe traveling through the asteroid belt hitting an asteroid is less than one in one billion, or less than a 0.000000001% chance. However, all of the asteroids combined only make up 4% of our Moon's mass.
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Ceres
Ceres is the largest asteroid in the asteroid belt, and the closest dwarf planet to the Sun. Ceres is very large for an asteroid, being 590 miles (950 km) in diameter. It has a very low mass at only about 896 billion megatons (896 zetagrams). It orbits the Sun at a distance of roughly 2.76 AU (257 million miles or 413 million km) and takes 4.6 Earth years to orbit the Sun once. Ceres is thought to have an atmosphere made of water vapor, caused by ice on its surface sublimating (going straight from a solid to a gas) when hit by sunlight. There is a mountain on the surface of Ceres known as Ahuna Mons. Ahuna Mons is thought to be a cryovolcano that shoots out freezing water or ice when it erupts, which would be where Ceres's atmosphere comes from. Ceres has a somewhat eccentric orbit around the Sun, having a higher orbital eccentricity than any planets except Mars and Mercury.
GREEK: Named after Demeter |
Jupiter
Jupiter is the fifth planet from the Sun, orbiting at a distance of 5.2 AU or 483,400,000 miles (778.5 million km). It is also the largest planet in the solar system with a diameter of 86,822 miles (139,820), which is almost 11 times as much as Earth's diameter and a mass of 1.898 quintillion megatons (1,898,000 yottagrams), which is over 317 times as much as Earth's mass. Jupiter is the first gas planet in the solar system, meaning that its surface is made of gas (mainly hydrogen, helium, methane, and ammonia). However, this is only the atmosphere of the planet, roughly 31 miles (50 km) thick. Below this is are layers of liquid hydrogen and helium. Closer to the core, the planet is composed of metallic liquid hydrogen, and it is thought to have a solid core made of rock and ice. Temperatures on Jupiter are very low, with the temperatures of the clouds reaching -234 °F (-148 °C). The pressure and temperature increase deeper in Jupiter. At the beginning of the metallic liquid hydrogen layer, temperatures are at 17,500 °F (9,704 °C), or hotter than the surface of the Sun. Temperatures at the core are thought to be as high as 64,300 °F (35,704 °C). Jupiter has at least 79 moons, the largest of which are Ganymede, Europa, Io, and Callisto.
GREEK: Named after Zeus |
Saturn
Saturn is the seventh planet from the Sun. It orbits at a distance of 9.58 AU, or about 891 million miles (1.43 billion km). One orbit around the Sun takes Saturn roughly 29 years. However, a day on Saturn is actually shorter than a day on Earth, lasting only 10 hours and 42 minutes. Saturn has a diameter of 72,367 miles (116,460 km), which is almost 10 times Earth's diameter. Although all of the gas planets in our solar system have rings, Saturn's ring system made of particles of ice and dust, is by far the largest. Although Saturn's rings reach up to 75,000 miles (120,700 km) away from Saturn, they are only 66 feet (20 meters) thick on average. Saturn is the least dense planet in the solar system, with a density of only 0.678 g/cm³, which means that Saturn could float in water (if there somehow was a body of water large enough). Saturn has 62 moons, plus countless tiny moonlets orbiting within Saturn's rings. Like Jupiter, Saturn is divided into a gaseous atmosphere, a liquid layer, and a solid core. Saturn's cloud layer is made of hydrogen, with layers below this of liquid hydrogen, then a layer of liquid metallic hydrogen and helium, and a rocky core in the middle.
GREEK: Named after Cronus |
Uranus
Uranus is the seventh planet from the Sun. It orbits the Sun at a distance of about 19.2 AU, or 1.78 billion miles (2.871 billion km). Uranus takes roughly 84 Earth years to complete an orbit around the Sun, and orbits at a speed of about 15,211 mph (24,479 kph). Uranus has a diameter of 15,759 miles (25,361 km), and has a mass of roughly 96 quadrillion megatons (86,810 yottagrams), or about 14.5 times Earth's mass. However, despite being much more massive than Earth, Uranus's gravity is slightly weaker than Earth's, with a surface gravity of only 8.69 m/s². Uranus does have rings, but they are made of very dark particles and are not as large as Saturn's rings. Uranus is tilted 97.7 degrees, meaning that it spins on its side. Uranus has at least 27 moons, with the largest being Titania, which has a diameter of 980 miles (1,577 km). Uranus is very cold, with the temperature at its cloud tops reaching as low as -371 °F (-224 °C). Like the other gaseous planets, it is composed of a gas layer, a liquid layer, and a rocky layer. The outer layer is composed of hydrogen, helium, and methane. The liquid layer is made of water, ammonia, and methane ices, and it has a solid core made of iron and nickel. Because Uranus and Neptune are made of substances heavier than hydrogen and helium, they are often referred to as ice giants.
GREEK: Named after Uranus who was thought of by the Greeks as the sky. Married to Gaea and father of the first twelve titans as well as the elder cyclopses and the hundred handed ones. |
Neptune
Neptune is the eighth and farthest planet from the Sun. It orbits at a distance of 30.11 AU, or 2.79 billion miles (4.5 billion km). Neptune has the longest year out of any planet in the solar system, taking 164.8 Earth years to go around the Sun once. However, a day on Neptune only lasts about 16 hours, which is about 67% of an Earth day. Neptune is about 3.88 times as large as Earth, with a diameter of 30,599 miles (49,244 km). Neptune is also the coldest planet in the solar system, with a minimum temperature of -392 °F (-236 °C). Because Neptune cannot be seen with the naked eye, it was not discovered until 1846. Neptune, like Uranus, is an ice giant. Its atmosphere and cloud layers are made of hydrogen, helium, and methane. The mantle is made of water, ammonia, and methane ices. In the center, like Uranus, there is a core of nickel and iron. Neptune has 14 moons. Its largest moon is Triton, which was discovered only days after Neptune itself. Neptune, like the other gas planets, has a ring system. Neptune has three main rings, with its total ring system reaching from 26,000 to 39,000 miles (41,843 to 62,764 km) out from Neptune itself. Neptune's surface gravity is slightly stronger than Earth's at 11.15 m/s².
GREEK: Named after Poseidon |
The Kuiper Belt
The Kuiper belt is a disc of small, asteroid-like objects, known as KBOs (Kuiper belt objects), stretching between 30 and 50 AU from the Sun. Pluto, Makemake, and Haumea are all located in the Kuiper belt, as well as Eris at some points during its orbit. It is around 20 times as wide as the asteroid belt. Many KBOs are made of frozen materials such as methane, ammonia, or water, instead of rock like most asteroids. Small objects in this area are classified into categories based off of how far they are from the Sun: Centaurs orbit between 5–29 AU from the Sun, Neptune Trojans orbit from 29–31 AU from the Sun, Trans-Neptunian (TNOs) objects orbit from 30–150 AU from the Sun, Extreme Trans-Neptunian objects (ETNOs) orbit from 150–2,000 AU from the Sun, and Oort cloud objects (OCOs) orbit from 2,000 to 200,000 AU from the Sun.
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Pluto
Pluto is the second dwarf planet, and the closest plutoid, or icy dwarf planet, to the Sun. It was once classified as a planet, but its status was changed to a dwarf planet in 2006. Pluto orbits at a distance of roughly 39.48 AU, or 3.66 billion miles (5.9 billion km). Pluto has an orbital eccentricity of 0.248, which is higher than any of the planets in the solar system, only being slightly higher than Mercury's orbital eccentricity of 0.205. Pluto is very small, with a diameter of only 1,476 miles (2,376 km). Although this is significantly smaller than our moon's diameter, it is still enough to make Pluto the largest dwarf planet in the solar system. Pluto also has a very low mass at only about 14.43 trillion megatons (13.1 yottagrams). This is only about 17% of the Moon's mass. Despite only being a dwarf planet, Pluto has five moons: Charon, Nix, Hydra, Kerberos, and Styx. Charon is by far the largest, with a diameter of 753.1 miles (1,212 km); this is more than half the size of Pluto itself. Hydra, which is Pluto's second largest moon, has a diameter of only 32 miles (51.5 km) across its largest dimension. Pluto's surface gravity is very weak, at only 0.62 m/s². Pluto's surface is also extremely cold, with an average temperature of -380 °F (-229 °C).
GREEK: Named after Hades |
Quaoar
Quaoar is a TNO and possible dwarf planet in the Kuiper belt. It orbits the Sun at an average distance of 42.83 AU, or 3.98 billion miles (6.4 billion km). It takes roughly 289 years to complete one orbit around the Sun. Because Quaoar orbits so far from the Sun, its average temperature is thought to be about -384 °F (-231 °C). It has an average diameter of 690 miles (1,110 km). Quaoar also has a single moon, Weywot. Weywot orbits Quaoar at an average distance of 9,010 miles (14,500 km). Weywot is very small, with an average diameter of 50 miles (81 km). There are thought to be cryovolcanoes on Quaoar's surface. Crystalline ice, likely from the cryovolcanoes, has been found on its surface, as well as frozen methane.
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Haumea
Haumea is the third confirmed dwarf planet from the Sun. It orbits very far from the Sun, at about 43.22 AU or 4.02 billion miles (6.47 billion km). Because it orbits so far from the Sun, its surface temperature is about -402 °F (-241 °C). Haumea rotates very fast; one day on Haumea lasts only about 3.9 hours, causing Haumea to be elongated. Haumea has an average diameter of 991.7 miles (1,596 km). Despite rotating very quickly, Haumea's year is very long. It takes Haumea over 284 years to complete one orbit around the Sun. Haumea has a relatively high orbital eccentricity of 0.191, although this is not as high as Pluto. Haumea has two moons, Hi'iaka and Namaka. They orbit very close to Haumea, with Hi'iaka, the farther-orbiting moon, orbiting at a distance of only 30,993 miles (49,878 km). Haumea's surface gravity is very weak, at only 0.401 m/s². Despite only being a dwarf planet, Haumea does have a small ring system. The rings are located 2,734 miles (4,400 km) from Haumea and are about 43.5 miles (70 km) wide. Haumea is the first Trans-Neptunian object (TNO) to have a ring system. Haumea has a very low mass, at only about 4.4 trillion megatons (4 yottagrams).
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Makemake
Makemake is the fourth dwarf planet from the Sun. It orbits at a distance of roughly 45.56 AU, or 4.23 billion miles (6.82 billion km). Haumea takes 357 years and 193 days to complete one orbit around the Sun. However, Makemake's day is very similar to an Earth day, lasting about 22.5 hours. It has an average diameter of 889 miles and has a low mass of 4.85 trillion megatons (4.4 yottagrams). Makemake has only one moon: MK2. MK2 has a presumed diameter of about 108.7 miles (175 km). Makemake has an extremely low surface temperature of only -405.6 °F (-243.2 °C). Makemake is thought to have almost no atmosphere, with an atmospheric pressure of only 4–12 nanobar, compared to Earth, which has an atmospheric pressure of about 1.013 bar. Makemake has a surface gravity of about 0.57 m/s². Makemake is also highly reflective, reflecting as much as 80% of the light that hits it. Because Makemake's surface is so cold, its surface is made of nitrogen and methane ices. This is most likely also the reason why Makemake is so reflective.
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Eris
Eris is, on average, the farthest confirmed dwarf planet from the Sun. It orbits at an average distance of 67.781 AU, or 6.3 billion miles (10.166 billion km) from the Sun. However, Eris's high orbital eccentricity of 0.44 means that it can sometimes orbit as close to the Sun as 37.911 AU, or 3.53 billion miles (5.72 billion km). It has the highest orbital period out of all the dwarf planets, taking 558 Earth years to circle the Sun one time. Eris has a diameter of 1,445 miles (2,326 km), making it very slightly smaller than Pluto. Despite this, Eris is the most massive dwarf planet in the solar system, due to its higher density. Eris has a single moon known as Dysnomia. Dysnomia has an average diameter of 435 miles (700 km) and orbits Eris at an average distance of 23,208 miles (37,350 km). Eris has an estimated surface temperature of -383 °F (-231 °C). Eris is known to have methane on its surface, which are theorized to sublime when Eris gets close enough to the Sun.
GREEK: Eris is the Greek goddess of Discord. |
Sedna
Sedna is an ETNO and possible dwarf planet that orbits the Sun at an average distance of 506.8 AU. However, its extremely high orbital eccentricity (0.855) means that it can orbit as close as 76.1 AU and as far as 936 AU. Because Sedna can orbit so far from the Sun, its surface temperature is estimated to be about -438 °F (-261 °C). Sedna's diameter is estimated at about 618 miles (995 km). NASA may send a mission to Sedna when it reaches its perihelion (closest point to the Sun) in 2075. Sedna's surface appears almost as red as Mars, which may be from hydrocarbons created by long-term exposure to the sunlight. Its surface is thought to also be made of methane and nitrogen ices, and possibly also water ice. Some studies have also suggested that Sedna may have an underground ocean of liquid water.
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External Links
- 3D Animation of the Solar System (Planet sizes are not to scale but distances between them are)