Planet Classification

Classification of the Planets and Their Physical Properties

(This Page is being reworked now that Pluto has been demoted)

The planets of the modern solar system are grouped into several different and sometimes overlapping classifications, as illustrated here:

The planets inside the orbit of the earth are called the Inferior Planets: Mercury and Venus.
The planets outside the orbit of the earth are called the Superior Planets: Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
The planets inside the asteroid belt are termed the Inner Planets (or the Terrestrial Planets): Mercury, Venus, Earth, and Mars.
The planets outside the asteroid belt are termed the Outer Planets: Jupiter, Saturn, Uranus, Neptune, and Pluto.
The planets sharing the gaseous structure of Jupiter are termed the Gas Giant (or Jovian) Planets: Jupiter, Saturn, Uranus, and Neptune.

The Nine (8) Planets is an overview of the history, mythology, and current scientific knowledge of each of the planets and moons in our solar system. Each page has text and images, some have sounds and movies, most provide references to additional related information.

Physical Properties of the Planets

MERCURY

Distance from the Sun:

Mean: 57.9 million km (0.387 astronomical units)

Max: 69.7 million km (0.467 a.u.)

Min: 45.9 million km (0.306 a.u.)

Sidereal period: 87.969 days

Synodic period: 115.88 days

Rotation period: 58.6461 days

Mean orbital velocity: 47.87 km/s

Axial inclination:

Diameter: 4878 km

Surface area: 7.475 x 10⁷

Density, water = 1:5.44

Mass: 3.3 x 10²⁶ g

Mass, Earth = 1:0.055

Volume, Earth = 1:0.056

Escape velocity: 4.25 km/s

Surface gravity, Earth = 1:0.38

Mean surface temperature:

Day +350°C

Night -170°C

Extremes of surface temperature:

Day +427°C

Night -183°C

VENUS

Distance from the Sun:

Mean: 108.2 million km (0.723 a.u.)

Max: 109 million km (0.728 a.u.)

Min: 107.4 million km (0.718 a.u.)

Sidereal period: 224.701 days

Synodic period: 583.9 days

Rotation period: 243.16 days

Mean orbital velocity: 35.02 km/s

Axial inclination: 178 deg

Diameter: 12104 km

Density, water = 1:5.25

Mass: 4.870 x 10²⁷ g

Mass, Earth = 1:0.815

Volume, Earth = 1: 0.86

Escape velocity: 10.36 km/s

Surface gravity, Earth = 1:0.903

Mean surface temperature:

Cloud tops -33°C

Surface +480°C

MARS

Distance from the Sun:

Mean: 227.94 million km (1.524 a.u.)

Max: 249.1 million km (1.666 a.u.)

Min: 206.7 million km (1.381 a.u.)

Sidereal period: 686.980 days

Synodic period: 779.9 days

Rotation period: 24 h 37 m 22.6 s

Mean orbital velocity: 24.1 km/s

Axial inclination: 23 deg 59 min

Diameter: 6794 km

Density, water = 1:3.94

Mass: 6.421 x 10²⁶ g

Mass, Earth = 1:0.107

Volume, Earth = 1:0.150

Escape velocity: 5.03 km/s

Surface gravity, Earth = 1:0.380

Mean surface temperature: -23°C

JUPITER

Distance from the Sun:

Mean: 778.34 million km (5.203 a.u.)

Max: 815.7 million km (5.455 a.u.)

Min: 740.9 million km (4.951 a.u.)

Sidereal period: 11.68 years

Synodic period: 398.9 days

Rotation period: 9 h 50 m 30 s

Mean orbital velocity: 13.06 km/s

Axial inclination: 3 deg 04 min

Diameter: 143884 km

Density, water = 1:1.33

Mass, Earth = 1:317.89

Volume, Earth = 1:1318.7

Escape velocity: 60.22 km/s

Surface gravity, Earth = 1:2.64

Mean surface temperature: -150°C

SATURN

Distance from the Sun:

Mean: 1427 million km (9.539 a.u.)

Max: 1507 million km (10.069 a.u.)

Min: 1347 million km (9.008 a.u.)

Sidereal period: 29.46 years

Mean synodic period: 378.1 days

Rotation period: 10 h 13 m 59 s

Mean orbital velocity: 9.6 km/s

Axial inclination: 26 deg 44 min

Diameter: 120536 km

Density, water = 1:0.71

Mass, Earth = 1:95.17

Volume, Earth = 1:744

Escape velocity: 32.26 km/s

Surface gravity, Earth = 1:1.16

Mean surface temperature: -180°C

URANUS

Distance from the Sun:

Mean: 2869.6 million km (19.181 a.u.)

Max: 3004 million km (20.088 a.u.)

Min: 2735 million km (18.275 a.u.)

Sidereal period: 84.01 years

Synodic period: 369.7 days

Rotation period: 17.24 hours

Mean orbital velocity: 6.90 km/s

Axial inclination: 98 deg

Diameter: 51118 km

Density, water = 1:1.27

Mass, Earth = 1:14.6

Volume, Earth = 1:67

Escape velocity: 22.5 km/s

Surface gravity, Earth = 1:1.17

Mean surface temperature: -214°C

NEPTUNE

Distance from the Sun:

Mean: 4496.7 million km (30.058 a.u.)

Max: 4537 million km (30.316 a.u.)

Min: 4456 million km (29.800 a.u.)

Sidereal period: 164.8 years

Synodic period: 367.5 days

Rotation period: 16.1 hours

Mean orbital velocity: 5.42 km/s

Axial inclination: 28 deg 48 min

Diameter: 50538 km

Density, water = 1:2.0643

Mass, Earth = 1:17.2

Volume, Earth = 1:57

Escape velocity: 23.9 km/s

Surface gravity, Earth = 1:1.2

Mean surface temperature: -220°C

Pluton:

PLUTO

Distance from the Sun:

Mean: 5900 million km (39.5 a.u.)

Max: 7375 million km (49.28 a.u.)

Min: 4425 million km (29.65 a.u.)

Sidereal period: 247.7 years

Synodic period: 366.7 days

Rotation period: 6 d 9 h 17 s

Mean orbital velocity: 4.7 km/s

Axial inclination: 122 deg .46

Diameter: 2324 km

Density, water = 1:2.0

Mass, Earth = 1:0.0022

Escape velocity: 1.18 km/s

Surface gravity, Earth = 1:0.06

Mean surface temperature: -230°C

Moons: Charon, Nix, Hydra

Introduction to the Night Sky - Part III
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Classification of the Planets and Their Physical Properties

Physical Properties of the Planets

Introduction to the Night Sky - Part III