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Planets in Order From the Sun

Our solar system is located in the Orion spiral arm of the Milky Way Galaxy and contains eight official planets that orbit counterclockwise around the Sun. The order of the eight official planets from the Sun, starting closest and moving outward:

  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune

Order of planets

Order of planets from the Sun. Universe Today

In addition to the planets, our solar system also includes dwarf planets, moons, asteroids, comets, and meteoroids. 

What is the Definition of a Planet?

There is an ongoing debate about the number of planets in our solar system. The most recent definition of a planet was released in 2006 by the International Astronomical Union (IAU), an organization responsible for classifying astronomical objects.

Their definition requires a planet to:

  • Orbit around the Sun,
  • Have enough gravity to force it into a spherical shape,
  • Have cleared away any other objects of similar size near its orbit around the Sun.

The Definition Debate 

Astronomers and planetary scientists did not unanimously agree with the new IAU definition and was contested by planetary scientists who prefer the geophysical definition of a planet.

When compared to the IAU planet definition, planetary scientist Alan Stern’s 2018 definition excludes the first point (that a planet be in orbit around the sun) and third point (that a planet has cleared the neighborhood around its orbit). Stern’s definition thus counts dwarf planets and planetary-mass moons as planets. 

Many professionals in the field also criticize the IAU definition of trying to limit the number of planets with the most recent change to the definition, as it was ultimately responsible for Pluto being removed as the ninth planet and re-labeled a dwarf planet. 

The IAU currently recognizes five dwarf planets:

  • Ceres
  • Eris
  • Haumea
  • Makemake
  • Pluto

Based on the geophysical definition of a planet, there are several satellite and dwarf planets in the solar system and likely more that haven’t been discovered.

Terrestrial, Giant and Dwarf planets

Geophysical classification of planets. Johns Hopkins APL/Mike Yakovlev

Planet Order from the Sun

All planets and dwarf planets recognized by the IAU will be included and separated by three categories of planets; Terrestrial, Giant and Dwarf planets.

Terrestrial and Giant Planets in order from the Sun 

Terrestrial Planets

Terrestrial planets include the four closest planets to the Sun located between the Sun and the asteroid belt; Mercury, Venus, Earth and Mars. Astronomers who use the geophysical definition of a planet would also include the Moon as a terrestrial planet. 

Terrestrial planets are planets with a solid surface, often made up of rock or metals. These types of planets also have few moons, a molten core and can have surface features like valleys, mountains and volcanoes. 

Terrestrial Planets

The terrestrial planets: Mercury, Venus, Earth and Mars, sized to scale.

Mercury image: NASA/JHUAPL Venus image: NASA/JPL-Caltech Earth image: NASA/Apollo 17 crew Mars image: ESA/MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

 

Mercury

Mercury is the closest planet to the Sun and is the smallest of the eight planets being only slightly larger than our moon. Mercury’s surface temperatures vary in extremes reaching day temperatures as high as 800°F (430°C) and dipping as low as -290°F (-180°C), lacking the atmosphere to hold the heat at night. 

One day lasts a long time on Mercury since the planet spins slowly – it takes 59 Earth days to make one full rotation. However, a year on Mercury goes fairly fast due to the proximity to the Sun. It takes only 88 Earth days, making it the fastest planet to orbit the Sun. 

Two spacecraft have visited Mercury, including Mariner (1974/75) and Messenger (launched in 2004). Messenger orbited Mercury over 4,000 times in four years then crashed into the planet’s surface after running out of fuel. In 2016, scientists released the first digital-elevation model of Mercury, which combined more than 10,000 images acquired by Messenger.

  • Diameter: 3,031 miles or 4,878 km
  • Distance from Sun: 0.4 Astronomical Units (AU)
  • Day: 59 Earth days
  • Orbit: 88 Earth days
  • Natural Satellites: None

Mercury

Mariner 10 image of Mercury. NASA

 

Above: I show my wife Ashley the planet, Mercury, for the first time using binoculars.

Venus 

Venus is the second planet from the Sun and is the second-brightest natural object in Earth’s night sky after the Moon. It is similar to Earth in size and mass and is known as Earth’s sister or twin planet. Venus’ rotation period of 243 Earth days is slower than any other planet and is one of two planets to rotate in the opposite direction (east to west).

Venus’ atmospheric conditions are an extreme example of the greenhouse effect. It’s thick, toxic atmosphere traps its heat resulting in temperatures upwards of 880 degrees Fahrenheit (471 degrees Celsius), making Venus the hottest planet in the solar system. 

Due to these atmospheric conditions, detailed explorations of Venus is difficult. It was the first planet visited by a spacecraft (Mariner 2) and the first to be successfully landed on (Venera 7) but the first detailed maps were not possible until the arrival of Magellan in 1991. 

  • Diameter: 7,521 miles or 12,104 km
  • Distance from Sun: 0.7 AU 
  • Day: 241 Earth days
  • Orbit: 225 Earth days
  • Natural Satellites: None 

Venus

Image of Venus using data from NASA’s Magellan spacecraft and Pioneer Venus Orbiter. NASA

 

Earth

Earth is the third planet from the Sun and it is the fifth-largest planet. Earth’s orbit around the Sun is 365.25 days, rotating on a tilted axis which is responsible for the four seasons. Earth’s gravity interacts with the Moon, it’s only natural satellite, helping to stabilize Earth’s axis orientation and slows its rotation causing tides. 

Approximately 29% of the Earth’s surface is land (i.e. continents and islands) with the remaining 71% covered with water (i.e. oceans, lakes, rivers and freshwater). Earth’s outer layer consists of several tectonic plates with a solid inner core and liquid outer core.  Earth’s atmosphere is rich in nitrogen and oxygen and several other gases in smaller amounts. 

Earth’s distance from the Sun, physical properties, and geological history have allowed life to evolve and exist on Earth. There are several million species of life on our planet with scientists believing there are more species that have yet to be discovered. 

  • Diameter: 7,926 miles (12,760 km)
  • Distance from Sun: 1 AU
  • Day: 23 hours, 56 minutes
  • Orbit: 365.25 Earth days 
  • Natural Satellites: the Moon

Earth

Image of Earth. NASA

Mars

Mars is the fourth planet from the Sun, known as the Red Planet from iron oxide (rust) in the soil. Mars is home to the highest known mountain and largest canyon and polar ice caps in both hemispheres that remain frozen year-round.

Due to its low atmospheric pressure, liquid water cannot exist on its surface, except at the lowest elevations for short periods of time. Surface features and data from space missions have led scientists to believe that water might have flowed along the surface of Mars and may still be inside underground rock. Scientific evidence also suggests Mars was once a much warmer planet.

Mars is one of the most explored planets in the solar system including missions to assess the habitability and possibility of life on Mars. The first spacecraft to visit Mars (Mariner 4), captured the first images of another planet from space.

Viking 1 was the first spacecraft to successfully land on the surface of Mars, and Sojourner, part of the Mars Pathfinder spacecraft, was the first robotic rover to operate on Mars. Additional astrobiology missions are planned with the Perseverance and Rosalind Franklin rovers.

  • Diameter: 4,217 miles (6,787 km)
  • Distance from Sun: 1.5 AU
  • Day: 24 hours, 37 minutes
  • Orbit: 687 Earth days
  • Natural Satellites: Deimos and Phobos

Mars

Mosaic of the Valles Marineris hemisphere of Mars. NASA

 

Above: I photograph the planet Mars as it approached opposition in 2020. 

Giant Planets 

Giant planets, also known as Jovian planets, are massive planets with a thick hydrogen and helium atmosphere, usually made of low-boiling-point materials (i.e. gases or ices). This includes Jupiter, Saturn, Uranus and Neptune. 

Jupiter and Saturn (the gas giants) are made up of mostly hydrogen and helium, whereas Uranus and Neptune are mostly composed of water, ammonia, and methane and are often referred to as ‘ice giants’.

Uranus and Neptune also have hazy atmospheric layers with small amounts of methane, giving them aquamarine colors.

Giant Planets

The four giant planets: Jupiter, Saturn, Uranus, and Neptune. Universe Today.

Jupiter 

Jupiter is the fifth planet from the Sun, the largest planet in our solar system and one of the brightest objects visible to the naked eye. It is composed mostly of hydrogen and helium with other trace gases. The outer atmosphere and internal heat have created cloud bands and the Great Red Spot – a giant storm that has lasted more than 300 years. Jupiter also has three faint rings that surround the planet. 

Jupiter also spins faster than any other planet, taking a little under 10 hours to complete a turn on its axis, compared with 24 hours for Earth. Jupiter’s four largest moons, known as the Galilean satellites (Ganymede, Callisto, Io, and Europa), show similarities to the terrestrial planets. 

There have been several fly-by missions of Jupiter, including Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Cassini and New Horizons.

These missions provided data on the Great Red Spot, revealed volcanoes on lo, helped create the first detailed maps of the Galilean satellites, discovered Jupiter’s rings and provided close up photos of the planet and largest moons. Future exploration will include the ice-covered liquid ocean of the moon Europa.

  • Diameter: 86,881 miles (139,822 km)
  • Distance from Sun: 5.2 AU
  • Day: 9.8 Earth hours
  • Orbit: 11.9 Earth years
  • Natural Satellites: 79 

Jupiter

Images of Jupiter, taken by NASA’s Hubble Space Telescope. NASA, ESA, and A. Simon

 Saturn 

Saturn, also known as the ringed planet, is the sixth planet from the sun and the second-largest planet. Saturn is pale yellow in color due to ammonia crystals in its upper atmosphere and features a prominent ring system made of ice and rock particles that range in size and orbit speeds. The rings are roughly 20 meters (66ft.) thick and extend from 6,630 to 120,700 km (4,120 to 75,000 mi) from the equator. 

Saturn has the second shortest day in the solar system taking only 10.7 hours to complete a full rotation. Similar to Earth, Saturn has a tilted orbital axis meaning Saturn also experiences seasons. Of Saturn’s approximately 60 moons, two of them (Titan and Enceladus) show signs of geological activity. 

The Cassini spacecraft was the largest interplanetary spacecraft ever built and spent more than ten years orbiting Saturn, including flybys of Venus, Earth and Jupiter. The mission ended in 2017 when it was low on fuel and was intentionally burned up in Saturn’s atmosphere to avoid the risk of contaminating Saturn’s moon.

During the end of its mission, Cassini traveled between the planet and the inner rings bringing it closer to Saturn than any other spacecraft.

  • Diameter: 74,900 miles (120,500 km)
  • Distance from Sun: 9.5 AU
  • Day: 10.5 Earth hours
  • Orbit: 29.5 Earth years
  • Natural Satellites: 62 

Saturn

Image of Saturn from the Hubble Space Telescope. NASA, ESA, A. Simon, M.H. Wong and the OPAL Team.

 

Above: I photograph the planet Saturn using an 11″ telescope in my backyard.

Uranus

Uranus is the seventh planet from the Sun and like Venus, rotates in the opposite direction as the other planets. Uranus is also the only planet to rotate on a sideways axis, meaning it rotates on its side with both poles facing east and west.

Like the other giant planets, Uranus also has 13 faint rings, although the outer rings are more brightly colored and easier to see. 

Uranus rings

Uranus’ tilted axis. Space.com (Image credit: NASA and Erich Karkoschka, U. of Arizona)

Uranus’ atmosphere contains gases similar to Jupiter and Saturn in addition to water, ammonia, and methane. The unique sideways tilt means that for nearly 84 Earth years the Sun shines directly over each pole and the opposite half of the planet experiences long, dark winters. It is the coldest atmosphere in the solar system with a minimum temperature of 49 K (−224 °C; −371 °F).

Voyager 2 remains the only investigation of Uranus, studying the structure and composition of the atmosphere, moons, and rings while also making additional discoveries. Voyager made its closest approach to the top of the clouds in 1986, before continuing to Neptune.

In 2009, an extension of the Cassini spacecraft mission to Uranus was evaluated but was rejected to move forward with destroying it in Saturn’s atmosphere. The extension would have taken Cassini 20 years to get to Uranus from Saturn. 

  • Diameter: 31,763 miles (51,120 km)
  • Distance from Sun: 19.2 AU
  • Day: 18 Earth hours
  • Orbit: 84 Earth years
  • Natural Satellites: 27

Uranus

Image of Uranus taken by the spacecraft Voyager 2. NASA/JPL-Caltech.

Neptune

Neptune is the eighth and farthest planet in our solar system. It is the fourth-largest planet and is similar to Uranus consisting of gases, ices, and has a series of moons and faint rings. Neptune was also the only planet whose presence was predicted using mathematics before it was observed visually through a telescope. This prediction was based largely on the changes in the orbit of Uranus.

Neptune has active and visible weather patterns driven by the strongest and fastest winds of any other planet in the solar system, reaching up to 1,500 mph (2,400 km/h). Neptune’s outer atmosphere is one of the coldest places in the solar system.

Voyager 2 is the only spacecraft to have visited Neptune, with a flyby in 1989. The mission confirmed the faint ring system that was discovered a few years earlier. Since the Voyager mission, additional observations continue to be made from ground-based telescopes. 

  • Diameter: 30,775 miles (49,530 km)
  • Distance from Sun: 30.1 AU
  • Day: 19 Earth hours
  • Orbit: 165 Earth years
  • Natural Satellites: 14

Neptune

Image of Neptune was taken by Voyager 2. NASA/JPL-Caltech.

Dwarf Planets in Order from the Sun

Beyond Neptune is the ‘trans-Neptunian region’, which is where Pluto and several other dwarf planets are found. To date, this region is largely unexplored.

As mentioned above, a dwarf planet is in direct orbit of the Sun and has enough gravity to pull its mass into a round shape.

However, dwarf planets do not have sufficient gravity to attract or push away smaller bodies in order to clear their orbit and therefore, do not fit the definition of a planet (according to the IAU).

The term dwarf planet, coined by Stern, was adopted by the IAU in 2006 as a category of sub-planetary objects. 

Related Video: What is a Dwarf Planet?

Ceres

Ceres is the smallest of the five dwarf planets but is the largest object found in the asteroid belt between Mars and Jupiter. It is also the closest dwarf planet to the sun and is the only dwarf planet inside the orbit of Neptune and not in the Kuiper belt. 

It was orbited by the Dawn spacecraft in 2015 but scientists are interested in exploring Ceres for possible signs of life due to the presence of water. 

Diameter: 940 km (584 mi)
Distance from Sun: 2.8 AU
Day: 9 Earth hours
Orbit: 4.6 Earth years
Natural Satellites: None

Pluto

Pluto is the ninth largest object orbiting the Sun and was known as the ninth planet until 2006 when the definition of a planet was changed, and it was reclassified as a dwarf planet.

Pluto is located in the Kuiper belt and has a different orbit when compared to the other planets in that it is both elliptical and tilted. The dwarf planet is made of ice and rock and is the largest trans-Neptunian object by volume and rotates similar to Venus and Neptune (spinning east to west). New Horizons remains the first and only spacecraft to fly by Pluto (2015). This historic voyage took nearly ten years and revealed some interesting and unexpected findings.

Diameter: 2376.6 km (1,476 mi)
Distance from Sun: 39 AU (can range from 30-49 AU)
Day: 153 Earth hours 
Orbit: 248 Earth years 
Natural Satellites: 5 (Charon, Styx, Nix, Kerberos, and Hydra)

Pluto

Enhanced image of Pluto, taken by New Horizons spacecraft. NASA/JHUAPL/SwRI.

Haumea

Haumea is around the same size as Pluto and is located in the Kuiper belt. It is one of the fastest rotating large objects in the solar system which causes its elongated shape. 

Haumea resides in the Kuiper belt and is roughly the same size as Pluto. It is one of the fastest rotating large objects in our solar system. Its fast spin distorts Haumea’s shape, making this dwarf planet look like a football. It is also the only Trans-Neptunian object to have a ring system

Diameter: 1,632 km (1,014 mi)
Distance from Sun: 43 AU 
Day: 4 Earth hours
Orbit: 285 Earth years
Natural Satellites: 2 (Hiʻiaka and Namaka.)

Makemake

The discovery of Makemake (and Eris) was part of the decision to change the definition of a planet. There are many aspects of this dwarf planet that remain unknown (structure, surface and atmosphere), but the surface does appear to be similar in colour to Pluto.

Like the other dwarf planets, Makemake is located in the Kuiper belt.

Diameter: 1,430 km (888 mil)
Distance from Sun: 45.8 AU
Day: 22.5 hours
Orbit: 305 Earth years
Natural Satellites: 1 provisional moon

Eris

Eris is the ninth-largest known object orbiting the Sun, the furthest from the Sun, and the largest object to have not been visited by a spacecraft.

Eris, which is larger than Pluto, was thought to be the tenth planet after its discovery until the IAU revisited their definition of a planet removing Pluto as a planet and classifying both Pluto and Eris as dwarf planets.

Diameter: 2,326 km (1,445 mi)
Distance from Sun: 96.3 AU
Day: 25.9 hours
Orbit: 557 Earth years
Natural Satellites: 1 (Dysnomia)

Our Galaxy Facts

  • Our solar system is located in the Orion Arm of the Milky Way galaxy’s spiral arm
  • The Milky Way galaxy is approximately 100,000 light-years in diameter
  • It takes our solar system approximately 230 million years to complete one orbit around the rotational center of the Milky Way
  • There are hundreds of billions of stars in the Milky Way galaxy, and most of those stars have their own planets, known as exoplanets

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