Mercury, Venus, Earth and Mars, the four planets nearest the Sun, are together called the:

Mercury, Venus, Earth and Mars are called terrestrial (or inner) planets because they are Earth-like: small, dense and made mostly of rock and metal.

Meaning of the word:

• "Terrestrial" comes from the Latin word "terra", meaning earth or land.
• These planets have solid, rocky surfaces on which a spacecraft could, in principle, land.

Common features of the terrestrial planets:

• They are made mainly of silicate rocks with a metallic core, mostly of iron and nickel.
• They have high densities compared with the outer planets.
• They are relatively small in size and mass.
• They have few or no moons.
• They do not have ring systems.

They have thin or moderate atmospheres. Mercury has almost no atmosphere, Venus has a very thick carbon dioxide atmosphere, Earth has a nitrogen-oxygen atmosphere and Mars has a thin carbon dioxide atmosphere.

Why the inner planets are rocky:

• When the solar system formed, billions of years ago, the region near the young Sun was very hot.
• Light gases and ices could not condense there, so only rocky and metallic materials formed the inner planets.
• Farther from the Sun, it was cold enough for ices to form, and the outer planets grew large enough to hold huge amounts of hydrogen and helium.

The outer planets:

• Jupiter, Saturn, Uranus and Neptune are called the Jovian or outer planets.
• They are much larger, have low density, thick gaseous atmospheres, many moons and ring systems.
• Jupiter and Saturn are called gas giants, while Uranus and Neptune are sometimes called ice giants.

Earth among the terrestrial planets:

• Earth is the largest of the terrestrial planets.
• It is the only known planet with liquid water on its surface and life.

Why not the other options?

• ✗Jovian planets, outer planets and gas giants are names for the four large planets beyond Mars.