• The inner planets are the planets in the internal
part of the Solar System that orbit closest to the
sun. The 4 inner planets are Mercury, Venus,
Earth, and Mars. There are a number of
differences between the inner and outer planets
aside from location. The inner planets are
composed mostly of rock, while the outer
planets are gas giants. Generally, inner planets
are both smaller and denser than their
counterparts. They also have few or no moons
and no rings circling them, while the outer
planets often have dozens of satellites and rings
composed of particles of ice and rock.
• Mercury is the closest planet to the Sun.
This small planet looks very much like the
Earth’s Moon and is even a similar grayish
color. It has no moons of its own and,
comprised mostly of iron and nickel, is one
of the densest planets in the Solar System.
Mercury has a very thin atmosphere,
which means that it is burning during the
day, up to 430°C, and freezing at night – as
low as -187 °C – because the atmosphere
can neither keep heat in or out.
• Venus is the hottest planet in the
solar system. Its atmosphere is a
thick cloud composed of various
gases, including carbon dioxide,
which traps the heat and transforms
the planet into a raging storm of
heat. Venus is often called the
morning star because, with the
exception of Earth’s moon, it’s the
brightest object in the sky. The
planet has no moon of its own
• Earth is the third inner planet and
the one we know best. Earth’s
atmosphere protects the planet from
dangerous radiation and helps keep
valuable sunlight in, allowing life to
survive. Like Mercury, the Earth has
an internal magnetic field. The
planet, which only has one moon, is
comprised of a mixture of various
rocks and minerals.
• Mars is the final inner planet, also known as the
Red Planet due to the rust of iron-rich materials
that form the planet’s surface. Mars’ thin
atmosphere has led some astronomers to
believe that water that once existed on the
planet might have actually leaked into space.
The planet has two small moons called Phobos
and Deimos. One of Mars’ best-known features
is its network of canals and canyons that led
many to believe there was life on Mars. Beyond
Mars are the four outer planets: Jupiter, Saturn,
Uranus, and Neptune.