The Solar System

Mercury

Venus

Earth

Mars

Asteroids

Earth’s moon

MercuryMercury

Jupiter

Saturn

Uranus

Neptune

NASANASA © UC Regents/Lick Observatory

Planetary orbits to scale. The Terrestrial

planets lie quite close to the sun, whereas

the Jovian planets are spread far from the

sun.

The planets and the

sun to scale. Saturn’s

rings would just

reach from Earth

to the moon.

Venus

Earth Moon

Mars

Jupiter

Saturn

Uranus

Neptune

Sun

Craters are common on all of the surfaces in

the solar system that are strong enough to

retain them. Earth has about 150 impact craters,

but many more have been erased by erosion.

Besides the planets, the asteroids and nearly all of

the moons in the solar system are scarred by

craters. Ranging from microscopic to hundreds of

kilometers in diameter, these craters have been

produced over the ages by meteorite impacts. When

astronomers see a rocky or icy surface that contains

few craters, they know that the surface is young.

Mercury is only 40 percent larger than Earth’s

moon, and its weak gravity cannot retain

a permanent atmosphere. Like the

moon, it is covered with

craters from meteorite

impacts.

Mercury

The distinction between the Terrestrial planets and

the Jovian planets is dramatic. The inner four planets,

Mercury, Venus, Earth, and Mars, are Terrestrial planets,

meaning they are small, dense, rocky worlds with little or no

atmosphere. The outer four planets, Jupiter, Saturn, Uranus,

and Neptune, are Jovian planets, meaning they are large,

low-density worlds with thick atmospheres and liquid or ice

interiors.

Of the Terrestrial planets, Earth is most massive, but

the Jovian planets are much more massive. Jupiter is

over 300 Earth masses, and Saturn is nearly 100 Earth

masses. Uranus and Neptune are 15 and 17 Earth masses.

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