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Planets of the Solar System

This page provides a brief description of each of the planets (and links to dwarf planets) of our solar system. You can also find out about the difference between planets, dwarf planets and small solar system bodies (SSSBs) here.

Solar System Map

Solar System Map - showing size, mass and orbital period, and orbit scale of planets & dwarf planets
Available as a poster here.

Planets

Dwarf Planets

The Planets of the Solar System

Planet Formation

The planets and the solar system were formed from a huge cloud of gases and dust particles left over when a massive star exploded as a supernova.

The gas drifted in space and it's thought that another supernova explosion nearby may have caused a pressure wave to pass through the cloud that caused clumping to coccur. As the matter clumped together, gravity in that area got stronger which attracted more matter which in turn increased the gravitational pull. As more and more matter fell toward the high density area, due to conservation of momentum it began to spin - rather like water going down a plug hole. The result was that as the gravity intensified, the spin became faster resulting in a flat disk of gas and dust surrounding a central high density sphere of gas.

Gravity was also working within the disk of rotating gas and dust pulling matter together to form primitive planets within the gas disk.

Eventually the temperature and pressures in the central sphere became so high that the atoms began fusing together (nuclear fusion) and the Sun ignited producing heat and light and also the solar wind - an outstreaming of subatomic particles.

The heat of the Sun and the solar wind immediately began to have an effect on the huge cloud of gas and particles in the disk. Volatile substances such as water ice near the Sun would heat and sublimate into gas, and these and other gases such as hydrogen would be gently accelerated away from the Sun by the solar wind.

At the distance of Jupiter, the temperature the Sun was not high enough to cause water ice to evaporate and so this meant that large quantities of solid material were available to build larger planets. These planets could therefore attract and keep hold of more of gas from the gas disk. This is one theory as to why the gas giants became so large, and why there is a divide in planet size between the small inner rocky planets and the outer gas giants.

As time continued, the workings of gravity and the solar wind eventually resulted in the solar system becoming as we know it today. A mostly empty space with eight surviving planets, five dwarf planets, a band of possibly millions of asteroids. All of this is thought to be surrounded by a cloud of icy comets - preserved remains of that early dust from which the solar system formed.

Planets and Dwarf Planets in Order from the Sun

The planets and dwarf planets are listed here in the order they are from the Sun. Click for more information on each.

Planet Mercury

  • The closest planet to the Sun - But not the hottest!
  • Has the shortest year and longest day
  • The Sun moves backwards for a while every day!
  • The smallest planet

Planet Venus

  • The hottest planet of the solar system
  • Rotates in the wrong direction!
  • The slowest rotating planet - but doesn't have the longest day
  • Closest planet to earth - In distance and in size

Planet Earth

  • Largest of the Inner planets
  • Densest planet of the solar system
  • Has (proportionally) the biggest moon of any planet
  • Is the only planet known to support life

Planet Mars

  • Last and coldest of the inner planets
  • Half the diameter of Earth
  • Has two tiny moons
  • After Earth, the most explored planet in the solar system

Dwarf Planet Ceres

  • The first of the dwarf planets
  • Largest object in the asteroid belt
  • Was considered to be a planet for 50 years
  • First dwarf planet to be visited by a spacecraft

Planet Jupiter

  • The largest planet of the Solar System
  • Has the most moons (79)
  • Has largest moon (Ganymede) which is bigger then Mercury
  • Has the shortest day of any planet

Planet Saturn

  • The second largest planet
  • Most extensive ring system of any planet
  • Rings less than 1km thick, but thousands of km wide.
  • Has a "great white Storm" which reoccurs every Saturnian year

Planet Uranus

  • The first planet to be discovered (e.g. was not known to early man)
  • Spins on it's side.
  • Has at least 13 rings all of which are darker than Saturn's
  • Only ever visited once (1986)

Planet Neptune

  • The eighth and final planet of the Solar System
  • Has the longest year (=165 Earth years) of any planet
  • Coldest temperatures of -220 degrees C
  • Ring system has arcs rather than rings

Dwarf Planet Pluto

  • Largest dwarf planet
  • Orbit is synchronised with Neptune's
  • Sometimes comes closer to the Sun than Neptune
  • Could be called a binary planet with Charon

Dwarf Planet Haumea

  • Shaped like an American football (1,960km x 1,518km x 996km )
  • Has a 4 hour day
  • Has two moons
  • Unexpectedly has a surface as bright as snow

Dwarf Planet Makemake

  • Spherical (1,430km diameter)
  • Reddish in color
  • Orbits nearly 30 degrees from the plane of the ecliptic
  • No moons detected

Dwarf Planet Eris

  • The most distant dwarf planet
  • It has a single moon called "Dysnomia"
  • Has an orbit lasting 557 Earth years
  • Was originally nicknamed "Xena"

Planet Nine?

  • Hypothetical planet that has not been discovered
  • Possibly four times the diameter of Earth
  • Possibly has a 15,000 year long orbit
  • A tiny needle in a huge haystack
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