Michael Paycer - The Planets
Astronomy · The Solar System · Michael Paycer

The Planets

Eight worlds circle the Sun, and no two are alike — from a sun-blasted ball of rock to a storm-wrapped giant that could swallow a thousand Earths. They fall into three families: the small rocky planets, the gas giants, and the ice giants. Here's how they compare, and a page for each.

Montage of the giant planets Jupiter, Saturn, Uranus and Neptune imaged by the Voyager missions

Image credit: NASA/JPL. The outer giants — Jupiter, Saturn, Uranus, and Neptune — as seen by the Voyager missions, whose Grand Tour of the 1980s gave us our first close look at all four.

Three Families

Rocky worlds, gas giants, ice giants

The terrestrial planets — Mercury, Venus, Earth, and Mars — are small, dense, and rocky, with solid surfaces you could stand on. Beyond the asteroid belt lie the gas giants, Jupiter and Saturn: vast balls of hydrogen and helium with no surface to speak of. Farther still are the ice giants, Uranus and Neptune — smaller, colder, and richer in the heavier "ices" of water, ammonia, and methane that tint them blue.

PlanetTypeAvg. distanceDayYearMoons
MercuryRocky0.39 AU59 days88 days0
VenusRocky0.72 AU243 days225 days0
EarthRocky1.00 AU24 hours365 days1
MarsRocky1.52 AU24.6 hours687 days2
JupiterGas giant5.2 AU9.9 hours11.9 years90+
SaturnGas giant9.5 AU10.7 hours29.5 years140+
UranusIce giant19.2 AU17.2 hours84 years28+
NeptuneIce giant30.1 AU16.1 hours165 years16+
The Eight Worlds

A page for each planet

Mercury

The smallest, fastest planet — a cratered ball of rock with wild temperature swings and ice hiding in its polar shadows. Not the hottest, despite being closest to the Sun.

Venus

Earth's scorching twin — the hottest planet of all, wrapped in crushing clouds of acid, spinning slowly and backwards. The brilliant "morning" and "evening star."

Earth

Our home and the only known living world — the "Blue Marble," the one planet not named for a god, seen whole for the first time only in our own lifetimes.

Mars

The rusty Red Planet — home to the tallest volcano and deepest canyon in the Solar System, a watery past, and the "canals" that never were.

Jupiter

The king of planets — a giant of storms and stripes with a centuries-old Great Red Spot, dozens of moons, and the mass of everything else combined.

Saturn

The jewel of the Solar System — its dazzling rings, its low density (it would float), and the strange hexagon at its north pole.

Uranus

The tipped-over ice giant that orbits on its side — the coldest planet, and the only one named for a Greek god rather than a Roman one.

Neptune

The windiest, most distant planet — a deep-blue world found by mathematics before it was ever seen, with supersonic storms and a captured moon, Triton.

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