Download The Inner Planets

27.1
KEY IDEA
The four planets closest to the
sun all have a rocky crust, dense
mantle layer, and very dense core.
KEY VOCABULARY
• inner planets
• outer planets
CLASSZONE.COM
Examine the vast distances between
planets in the solar system.
Keycode: ES2701
The Inner Planets
The sun is at the center of the solar system. Around it orbit nine planets,
each with unique characteristics. Although astronomers have known about
the existence of other planets for centuries, it’s only within the last few
decades that technology has given scientists an up-close look at our
nearest neighbors in space.
Two Planetary Neighborhoods
The planets in our solar system are divided into two groups. The four
nearest the sun—Mercury, Venus, Earth, and Mars—are called the inner
planets. All of the inner planets have rocky crusts, dense mantle layers,
and very dense cores. Because of their earthlike characteristics, these
planets are sometimes called the terrestrial (earthlike) planets.
Just beyond the orbit of Mars is a belt of small bodies called asteroids.
This asteroid belt separates the inner planets from the outer planets,
Jupiter, Saturn, Uranus, Neptune, and Pluto. The first four of these planets,
called the Jovian, or Jupiter-like, planets, are considerably larger than
Earth. They are gaseous, with an outer layer that is mostly hydrogen gas.
Closer to the planet’s center, the hydrogen is compressed to a hot liquid.
The Jovian planets are much less dense than Earth, and all have ring
systems.
Pluto is the oddity of the solar system. It is not dense enough to be
considered a terrestrial planet, and it is too small to be a Jovian planet. You
will read more about the outer planets in the next section.
THE SOLAR SYSTEM This illustration shows the relative sizes of the planets but
does not represent the distance between them.
The Inner Planets
The
Asteroid
Belt
Mercury
588
Venus
Earth
Mars