The Planets

Definition of a Planet IAU definition: 1) orbiting a star or stellar remnant 2) enough mass to be rounded by gravity 3) no fusion reaction at core 4) cleared its own orbit of planetessimals

Eight Planets The solar system has eight planets

Terrestrial Planets

Mercury

Mercury Orbital radius: 0.38 AU Orbital period: 0.24 a Composition: large iron core, rocky mantle Atmospheric composition: thin and unstable (low gravity) Mean surface temperature: 340 K

Mercury Mass: 0.06 Earths Satellites: None Unique features: Fastest orbital period, strong magnetic field

Venus

Venus Orbital radius: 0.72 AU Orbital period: 0.62 a Composition: unknown, but similar to Earth Atmospheric composition: thick, CO2 and N (93 times thicker than ours) Mean surface temperature: 735 K

Venus Mass: 0.815 Earths Satellites: None Unique features: heavy volcanism, low magnetic field

Earth

Earth Orbital radius: 1 AU Orbital period: 1 a Composition: core, mantle, crust Atmospheric composition: just right Mean surface temperature:

Earth Mass: 1 Earth Satellites: Luna Unique features: I live there

Mars

Mars Orbital radius: 1.5 AU Orbital period: 1.9 a Composition: Iron core, silicate mantle, crust Atmospheric composition: Thin, CO2 and other gasses Mean surface temperature: 227 K

Mars Satellites: Deimos and Phobos Unique features: Once had a magnetosphere, red colour caused by iron core, hematite and geological structures suggest there was once liquid water

Jupiter

Jovian Planets

Jupiter Orbital radius: 5.2 AU Orbital period: 11.9 a Composition: small rocky core surrounded by liquid metallic H Atmospheric composition: hydrogen and helium Mean temperature at 1 bar: 165 K

Jupiter Mass: 318 Earths Satellites: 63 Unique features: Largest planet, great red spot, has a ring structure

Jovian Satellites 63 moons, including the Galilean moons: Io  most volcanically active body Ganymede  largest moon; magnetic field Europa  covered with ice; possible water Callisto  heavily cratered; small atmosphere

Io

Europa

Ganymede

Callisto

Saturn

Saturn Orbital radius: 9.5 AU Orbital period: 30 a Composition: Small rocky core surrounded by liquid H Atmospheric composition: Hydrogen and helium Mean temperature at 1 bar: 134 K

Saturn Mass: 95 Earths Satellites: 60 Unique features: Pronounced ring system, less dense than water

Hexagonal polar cloud (Voyager)

Saturn’s Satellites 60 satellites including: Titan  dense atmosphere, evidence of liquid water

Titan

Uranus

Uranus Orbital radius: 19 AU Orbital period: 84 a Composition: icy core Atmospheric composition: hydrogen and helium Mean temperature at 1 bar: 53 K

Uranus Satellites: 27 Unique features: Largest axial tilt (almost on the side … continuous day or night),

Uranian Satellites 27 including: Miranda  water ice surface

Miranda

Neptune

Neptune Orbital radius: 30 AU Orbital period: 165 a Composition: Icy core Atmospheric composition: hydrogen and helium; trace methane Mean surface temperature: 72 K

Neptune Mass: 17 Earths Satellites: 13 Unique features: last planet, blue colour from methane

Neptunian Satellites 13 including: Triton  retrograde synchronous orbit

Pluto

Pluto

HD 209458B