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inner planetsclick to hear

Rocky planets closest to the Sun; located inside the asteroid belt.
inner planets asteroid belt Mercury Venus Mars Earth 1 astronomical unit

asteroid belt click to hear

Circular region between Mars and Jupiter containing the greatest number of asteroids; marks the boundary between the inner and outer planets.

Mercury click to hear

The planet closest to the Sun; devoid of atmosphere, heavily cratered and marked by extreme variations in temperature (-300°F to 800°F).

Venus click to hear

Second planet from the Sun; its density and chemical composition are similar to those of Earth.

Mars click to hear

Fourth planet from the Sun; its crust contains iron oxide, giving Mars its reddish color.

Earth click to hear

Third planet from the Sun, inhabited by humankind; up to now, the only planet with evidence of life.

1 astronomical unit click to hear

Unit of distance equal to the mean distance between Earth and the Sun, equivalent to about 93 million mi.