What is a planet?

Orbit

The path an object takes as it revolves around the sun.

Spherical shape

A three-dimensional shape that is round and symmetrical, like a ball.

Dwarf planet

A celestial body that orbits the sun, has a rigid, almost spherical shape, can share its orbit with other bodies, and is not a satellite.

Moon

A natural satellite that orbits a planet.

Small solar system body (SSSB)

Any object in the solar system that is not classified as a dwarf planet or moon.

Terrestrial planets

Planets similar in size and density to Earth, including Mercury, Mars, Venus, and Earth.

Jovian planets

Planets with lower densities, primarily composed of light elements, gases, and ices, including Jupiter, Saturn, Uranus, and Neptune.

Gas giants

A term used to describe the Jovian planets due to their large size and gaseous composition.

Inferior planets

Planets that are closer to the sun than Earth, specifically Mercury and Venus.

Superior planets

Planets that are farther from the sun than Earth.

Retrograde motion

The apparent backward movement of a planet in the sky as observed from Earth.

Astronomical Unit (au)

A unit of length that represents the average distance between Earth and the Sun.

Mercury

The planet that is 0.39 au from the sun, covered with craters and maria, and is the smallest planet.

Venus

The planet that is 0.72 au from the sun, has an opaque atmosphere, is closest in size to Earth, and has an extremely hot surface.

Earth

The planet that is 1 au from the sun and supports life.

Mars

The planet that is 1.52 au from the sun, has a reddish color, a thin atmosphere, and two tiny moons.

Olympus Mons

The longest volcano in the solar system, located on Mars.

Gas giants

Planets that emit more energy than they receive from the sun, with Uranus emitting almost no excess energy.

Jupiter

The largest and most massive planet, located 5.20 au from the sun, with a noticeable equatorial bulge and many moons.

Saturn

The planet located 9.6 au from the sun, known for its ring system and the largest moon, Titan, which has its own atmosphere.

Uranus

The planet located 19.2 au from the sun, discovered in 1781, known for its unusual tilt and strange magnetic field.

Neptune

The planet located 30.1 au from the sun, discovered in 1846, resembling Uranus and having two large moons.