Solar System Planet Facts

The Solar System is made up of the Sun, eight planets, five dwarf planets, over one hundred sixty moons, half a million asteroids, more than three thousand comets, dust, and gas.

The accepted theory for the formation of the Solar System states that a cloud of gas and dust–known as a solar nebula–was disturbed by some outside force, causing the cloud to rotate and condense. As the cloud compressed, particles in the outer disk began to stick together forming increasingly larger objects until ultimately the planets were formed. While the planets were forming in the out disk region, the particles in the center of the disk continued to compress, eventually causing temperatures and pressure to reach such extremes that nuclear fusion began to take place, and thus the Sun was born.

The Solar System is over 4.5 billion years old.

Our solar system is only one in an estimated several billion in the Milky Way Galaxy.

Regions of the Solar System

  • The inner Solar System consists of the rocky terrestrial planets Mercury, Venus, Earth, and Mars.
  • The Asteroid Belt between the orbits of Mars and Jupiter.
  • The outgas giant planets consisting of Jupiter, Saturn, Uranus, and Neptune.
  • The Kuiper Belt, a region (ring) of asteroids and comets lying beyond the orbit of Neptune.
  • The Oort Cloud, a spherical shell that is made up of dormant comets.

By some definitions, the size of the Solar System is almost two light-years!

Earth Facts

  • The word “Earth” comes from the Old English word “ertha,” meaning ground or land.
  • Despite what is commonly believed, the Earth has been known to be (roughly) spherical since antiquity.
  • Earth is the only known body in the universe to possess life.
    Until the 16th century, the Earth was believed to be the center of the universe, with all objects orbiting around it.
  • Earth’s atmosphere is composed of 78% nitrogen, 21% oxygen, and trace amounts of other gases including argon and carbon dioxide.
  • The substantial amount of oxygen found on Earth is the result of plantlife’s consumption of carbon dioxide during the process of photosynthesis.
  • An important component of Earth’s atmosphere is the Ozone Layer— “shell” of a special type of oxygen that protects the Earth from harmful solar radiation.
  • Oceans cover over 70% of Earth’s surface.
  • The first life on Earth developed in the oceans.
  • Earth’s water was initially trapped within the planet; however, over time this water was brought to the surface as a result of the planet’s volcanic activity.
  • Only 30% of Earth’s surface is dry land.
  • Compared with other solid bodies in the Solar System, the Earth’s surface has relatively few visible impact craters. The lack of craters is due to Earth’s geological processes reshaping its surface.
  • Earth’s highest point is Mount Everest. Its height is 8.8 km.
  • Earth’s lowest point is Challenger Deep, found 10.9 km beneath sea level.
  • Earth is the fifth largest planet in the Solar System and largest of the terrestrial planets.
  • The orbit of Earth is one of the most circulars of all the planets.
  • One year on Earth last a little over 365 days. This “little over” part is almost 1/4 of a day, and hence the reason we have a leap year every 4 years.
  • The axis around which Earth rotates is tilted 23°. The effect of this tilt is the different seasons we experience.

Jupiter Facts

  • Jupiter has been known to humanity since antiquity due to it being visible to the naked eye. However, it was believed to be a star by ancient peoples and only within the last several hundred years was it realized to be a planet.
  • The name Jupiter comes from the ancient Romans. In their mythology, Jupiter was the king of the gods.
  • In old Norse mythology, Jupiter was connected with the God Thor. We get the word “Thursday” from Thor, as in “Thor’s day”.
  • The discovery of four of Jupiter’s moons by Galileo in 1610 was the first proof that there are celestial bodies orbiting something other than the Earth. This was strong evidence in support of Copernicus’ Sun-centered model of the Solar System.

  • It takes Jupiter 11.86 (Earth) years to orbit the sun.
  • Jupiter has at least 67 moons.
  • Ganymede, Jupiter’s larger moon, has a diameter larger than Mercury.
  • Jupiter rotates very quickly, taking slightly less than 10 hours to complete one rotation of its axis. This is the quickest of all the planets in the Solar System.
  • As a result of its quick rotation, Jupiter has an oblate shape, meaning that it bulges around the equator as if it has been squashed.
  • Jupiter has very faint rings around it, mostly comprised of dust. Scientists believe that the main ring was formed out of material from two of Jupiter’s moons.
  • The magnetic field of Jupiter is 14 times the strength of Earth’s, which is the largest of any planet in the Solar System.
  • Jupiter is the only planet that has a center of mass with the sun that lies outside the sun itself.
  • The axis of Jupiter is only tilted by 3.13 degrees, meaning Jupiter does not experience seasons like Earth.
  • The adjective form of the word Jupiter is “Jovian” (for example, the largest Jovian moon is Ganymede). It used to be “jovial” but that now means happy, which was the mood associated with Jupiter in the past.
  • Jupiter’s Great Red Spot is an enormous storm that has been raging for over 300 years. This storm is so wide that two Earth’s would fit inside of it.
  • If Jupiter had been 80 times more massive nuclear fusion would have occurred in its core. Thus Jupiter would have become a star rather than a planet.

Uranus Facts

  • William Herschel discovered Uranus in 1781, making Uranus the first planet discovered in modern history.
  • It takes Uranus roughly 84 (Earth) years to orbit the sun.
  • The axis of Uranus is 98 degrees, so it almost lies sideways as it orbits the sun. In other words, the north and south poles on Uranus lie near where the equator is on Earth.
  • Scientists don’t know why Uranus is tilted so much, while the other planets are not. One theory is that an Earth-sized planet crashed into it and forced its axis to shift.

  • As Uranus is tilted so much, its poles receive more energy from the sun than its equator. However, its equator is actually hotter. The reason for this is not currently known.
  • The wind on Uranus can reach speeds of 900 kilometers per hour (560 miles per hour).
  • Uranus has a mass of about 14 and a half times the mass of Earth. This makes it the lightest of the four gas giants.
  • Uranus is the second least dense planet in the Solar System, after Saturn.
  • Scientists believe that Uranus has a rocky core in the center, an icy mantle in the middle and an outer gas layer.
  • Uranus was the second planet in the Solar System to be observed to have rings.
  • The chemical element uranium, discovered in 1789, was named after the newly discovered planet Uranus.
  • The gravity on Uranus is only 91% of the gravity on Earth.
  • In 1977, Uranus was discovered to have a ring system. This ring system is extremely faint compared to the ring system of Saturn.

Mercury Facts

  • Mercury has been known to humanity since ancient times (approximately 3,000 B.C.)
  • Early civilizations believed Mercury was actually two different stars–one that appeared in the morning and one that appeared in the evening.
  • Mercury is named after the messenger of the Roman gods.
  • It wasn’t until Copernicus put forth his Sun-centered model of the Solar System in the 1500s that is was realized Mercury is a planet.
  • Mercury has no moons or rings.

  • It was once believed that a planet called Vulcan existed between the orbit of Mercury and the Sun.
  • It takes Mercury just under 88 (Earth) days to orbit the sun.
  • Mercury orbits the sun in an ellipse, not a circle. In fact, it’s orbit is the least like a circle of all the planets and scientists say it has the most “eccentric orbit” in the Solar System.
  • The temperature on Mercury ranges from -170C (-280F) during the night to 430C (800F) during the day. This is the most extreme temperature change of all the planets.
  • Mercury’s axis has the smallest tilt of any of the planets in the Solar System, meaning that there are no seasons on its surface.
  • Mercury rotates three times during two orbits of the sun. It is the only planet that doesn’t rotate exactly once every year.
  • The orbit of Mercury was important in proving Albert Einstein’s theory of General Relativity.
  • Mercury is the second densest planet in the Solar System. Only Earth has a higher density.
  • Mercury has a large iron core in its center whose radius is 1800 to 1900 kilometers (1100 to 1180 miles).
  • Scientists believe the core of Mercury is probably molten.
  • The outer shell of Mercury is only 500 to 600 kilometers (310 to 375 miles) thick. Earth’s outer shell (the mantle and crust) is 2930 kilometers (1819 miles) thick.
  • Mercury has a very thin atmosphere, which is made up of atoms from the surface of the planet that have been blown away by solar winds. As Mercury is so hot, these atoms quickly escape into space and so its atmosphere is constantly being replenished.
  • Mercury has a weak magnetic field whose strength is about 1% of the magnetic field on Earth.

Venus Facts

  • Venus is the brightest object in the sky after the Sun and the Earth’s moon.
  • Ancient humans believed Venus to be two distinct stars, a morning star and an evening star.
  • Venus is named after the Roman goddess of love.
  • Earth and Venus are often called twin planets because of their similar size and position in the Solar System.

  • Venus has no moons nor rings.
  • Scientists believe that Venus once possessed large amounts of water. However, due to the high temperatures produce from the extreme greenhouse effect, this water boiled off long ago.
  • It takes Venus just under 225 (Earth) days to orbit the sun.
  • Venus has a very, very slow rotation about its axis. One “day” on Venus the time Venus to complete one rotation takes 243 (Earth) days. This means that a year on Venus lasts only about 2 days!
  • It rotates counter-clockwise, unlike the other planets in the Solar System.
  • The temperature on the surface of Venus is 462C (863F), making it the hottest of all the planets in the Solar System.
  • The temperature on Venus doesn’t vary much between the night and day because of the slow movement of the winds across its surface.
  • The surface of Venus is estimated to be between 300 and 400 million years old. Earth’s surface is about 100 million years old.
  • Venus has a very weak magnetic field. This surprised scientists, who expected Venus to have a magnetic field similar in strength to Earth’s.
  • Venus is the only planet in the Solar System to be named after a female figure.
  • Very little is known about the interior of Venus, but it is thought to have a similar structure to Earth with a core, mantle, and crust due to its similar size.
  • Venus orbits the sun in an ellipse, but its orbit is the closest to being a circle out of all the planets in the Solar System.
  • When Venus is in line with Earth and the sun, it is the closest planet to us, at an average distance of 41 million kilometers (25.5 million miles) away.

Mars Facts

  • Mars is the 4th planet from the Sun and last of the terrestrial planets.
  • Mars is named after the Roman god of war.
  • A common nickname for Mars is “The Red Planet.”
  • Many people once believed Mars to possess intelligent life. This belief resulted from the discovery of lines that appeared to be too straight to occur naturally. It was later discovered, however, that the lines weren’t as straight as previously believed, and thus it was realized that there was no proof for intelligent life on Mars.
  • Of all the planets other than Earth, Mars is the most hospitable to life.

  • Martians, or extraterrestrials from Mars, are a common character in science fiction books and movies.
  • It takes Mars 687 (Earth) days to orbit the sun.
  • Mars is the only planet, other than the Earth, that has polar ice caps. They are called Planum Boreum (northern cap) and Planum Australe (southern cap).
  • Mars is tilted on its axis by about 25.19 degrees, which is similar to the axial tilt of the Earth (22.5 degrees). This means that Mars has seasons like the Earth, although they last nearly twice as long.
  • Mars has the second most eccentric orbit out of all the planets in the Solar System, which means that its orbit is the second least like a circle.
  • In the book ‘Gulliver’s Travels’, the author Jonathon Swift wrote about two moons of Mars, about 150 years before they were discovered.
  • Mars has no magnetic field, although some scientists believe that Mars did have a magnetic field about 4 billion years ago.
  • Water ice has been found under the surface of Mars, mostly below the polar caps.

Saturn Facts

  • Saturn is the sixth planet from the Sun and last of the planets known to ancient civilizations.
  • In Roman mythology, Saturn was the father of Jupiter, king of the gods. This relationship makes sense given that the planets Saturn and Jupiter are similar in so many respects, including size and composition.
  • The most common nickname for Saturn is “The Ringed Planet,” a nickname arising from the large and beautiful ring system that encircles the planet.

  • An unusual quality of Saturn is that it gives off more energy than it receives from the Sun. This heat is believed to be generated from the planet’s gravitational compression as well as the friction created by the large amounts of helium found in the atmosphere.
  • It takes Saturn 29.5 (Earth) years to orbit the sun.
  • The winds on Saturn are by far the fastest of any planet in the Solar System. They have been measured at 1,800 kilometers per hour (1,100 miles per hour).
  • Saturn is the least dense planet in the Solar System. It has a density less than water, so it would float!
  • Titan is the second-largest moon in the Solar System, behind Jupiter’s moon.
  • It takes Saturn an average of 10 and a half hours to complete one rotation about its own axis.
  • Saturn appears a pale yellow color because its upper atmosphere contains ammonia crystals.
  • The magnetic field on Saturn is slighter weaker than Earth’s magnetic field.
  • Even though Saturn is called a gas giant, scientists believe it has a solid core.
  • Saturn and Jupiter together contain 92% of all the mass from the planets in the Solar System.
  • The interior of Saturn is very hot, reaching temperatures of up to 11,700C (21,000F).
  • The outer atmosphere of Saturn contains 96% hydrogen and 3% helium. The rest is made up of small amounts of other elements, although scientists do not know their exact quantities.
  • The average distance from the sun to Saturn is more than 1.4 billion kilometers (0.9 billion miles).

Neptune Facts

  • It takes Neptune roughly 165 (Earth) years to orbit the sun.
  • On 11 July 2011, Neptune made one complete orbit of the sun from the day it was discovered, i.e. it was the first complete Neptune year since it was discovered.
  • Jean Joseph Leverrier discovered Neptune, and as a result, Neptune was initially called Leverrier. This name, however, quickly was abandoned and the name Neptune was chosen instead.
  • Neptune is the Roman God of the Sea. In Greek, Neptune is called Poseidon.

  • The gravity on Neptune is the second largest of any planet in the Solar System, behind only Jupiter.
  • Neptune orbits the sun at approximately 30 times the distance from the Earth to the sun.
  • The discovery of Neptune’s largest moon Triton occurred just 17 days after the discovery of Neptune itself.
  • Neptune possesses a storm similar to the Great Red Spot found on Jupiter. This storm is commonly referred to as the Great Dark Spot. Its size is roughly that of Earth.
  • The is a second storm on Neptune known as the Small Dark Spot. It is the size of Earth’s moon.
  • During the Voyager 2 mission to Neptune, it took 246 minutes (4 hours and 6 minutes) for signals from the spacecraft to reach Earth.
  • Like the other outer planets, Neptune possesses a ring system, though its rings are very faint.
  • The average temperature on Neptune is -214C (-353F).

Space Links

  • A Planet Pursuit – Pictures, facts and general information on the nine planets.
  • Astromaterials Curation – Features Moon rocks, Mars meteorites, and space exposed materials at NASA’s curation office.
  • Astronomy 161: The Solar System – Overview with historical background and basic astronomy concepts, details about planets, satellites, asteroids, comets, and meteors.
  • Astronomy Today – Solar System – Fairly detailed information about our sun and its planets.
  • BBC Space: Solar System – 3D tour including videos with audio and text information on the Sun and the bodies orbiting around it.
  • Bob the Alien’s Tour of the Solar System – Informative tour of the planets, dwarf planets, moons, asteroids and comets in the Solar System and the stars and galaxies beyond. Also provides information about space exploration and astronomy.
  • Computing Planetary Positions – A detailed online tutorial on how to compute planetary locations using math formulas.
  • Exploring the Planets – Sponsored by the National Air and Space Museum contains many interesting facts about the planets, pictures, comparisons and a section dedicated to spacecraft.
  • Free Software for Planetary Science – Image processing browsers for Mariner 6, 7, 9, 10, Venera 15/16, and Viking Orbiter.
  • Gazetteer of Planetary Nomenclature – Protocols for naming planetary features, by the Working Group for Planetary System Nomenclature of the International Astronomical Union.
  • Gravity Calculator – Allows the user to perform various gravity calculations for the sun and planets based on Isaac Newton’s law of universal gravitation.
  • The Nine Planets – Overview, sections dedicated to each planet and the smaller bodies – with data, information and some pictures – glossary and appendices.
  • Northeast Regional Planetary Data Center – Includes a list of available image collections and how to obtain the data at the facility (no images are online).
  • Nova Celestia – Provides an overview and original illustrations of elements.
  • Orrery: Solar System Simulator – A Java applet that simulates gravitating masses. Features a working model with motions and sizes of 70 planets and moons to scale.
  • Orrery: The Solar System in Action – A concise tour containing numerous educational resources, and support for Spacetech’s Orrery application.
  • Our Existenz – Provides photographs and information on the planets of our solar system.
  • Planetary Alignment and Magnetic Field Interaction – Article by David W. Allan on the magnetic field interactions in planet alignments and the correlation of sunspot activity to periodic field polarity reversals.
  • Planetary Cartography and Graphics by Ralph Aeschliman – Planetary maps and graphics of Mars, the Moon, and Venus.
  • Planetary Fact Sheet – Table of essential measurements and facts regarding the nine planets with links to highly detailed summaries.
  • Planetary Interactions – Cycles, resonances, synchronizations and interactions in the solar system.
  • Planetary Science Institute – Research and educational institute with projects to study planets, asteroids, and comets.
  • Shaker Effects in Celestial Mechanics – Article by Franz Heeke about the rotation of the sun and planets, the sun’s motion around the center of mass of the solar system, planetary rings, solar activity, and climate, and the origin of the solar system.
  • SkyScopes – Information about planetary astronomy and space exploration and habitat. Online chat, message boards, and related links. Sells replicas and toys.
  • Smiley’s Planet – Explore the solar system’s planets. Includes pictures, descriptions, statistical information and a special section on the latest voyage to Mars.
  • Solar System Dynamics – Provides detailed information related to known bodies in orbit around the Sun. Ephemerides, physical parameters, Earth close-approaches, observer tools.
  • Solar System Dynamics – Web-based resources accompanying the book of this name, by Carl D. Murray and Stanley F. Dermott.
  • Solar System Exploration Home Page – The Solar System Exploration Home Page is part of NASA’s Office of Space Science and describes NASA’s program to explore the solar system.
  • Solar System Simulator – Online software that generates views of the bodies of our planetary system at any date from any artificial or natural point of observation.
  • Solar System Simulator – Shows the position of the planets as they rotate around the sun for many years to come.
  • Stardate Online: Guide to the Solar System – Contains an outline of the formation and evolution of planets, comets, asteroids, and of their features and exploration.
  • The Solar Space Station – Facts, descriptions, and pictures, with sections about the Sun, the planets and meteors and asteroids.
  • The Solar System – History of and basic facts about major solar system bodies.
  • USGS Astrogeology Research Program – Features planetary imagery, research, GIS, mapping, and image processing software. The site provides information about the group and about the Solar System.
  • Views of the Solar System – Multimedia tour with statistical data, detailed information, pictures, and videos. Also includes educational resources.
  • Welcome to the Planets – Select images from NASA’s planetary exploration program.
  • Windows to the Universe – Aimed at portraying Earth and Space Sciences in a fun way. Includes information about space weather, global space physics and a real-time movie of current solar activity.