About Moons
Moons are natural satellites that orbit planets, dwarf planets, and even some asteroids. They range from tiny irregular rocks to worlds larger than the planet Mercury. Some are geologically active, and several may hide oceans beneath icy crusts.
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Earth's Moon
Our Moon is the only world beyond Earth where humans have walked.
Learn MoreEuropa
Europa may hide a global ocean beneath its icy surface.
Learn MoreGanymede
Ganymede is the largest moon in the Solar System.
Learn MoreIo
Io is the most volcanically active world known.
Learn MoreTitan
Titan has a thick atmosphere and lakes on its surface.
Learn MoreEnceladus
Enceladus sprays water-rich plumes from cracks near its south pole.
Learn MorePhobos
Phobos is a small, irregular moon that orbits very close to Mars.
Learn MoreMoon Systems
The giant planets have large families of moons.
Learn MoreEarth's Moon
The Moon formed very early in Solar System history and has a heavily cratered surface. Dark plains called maria were created by ancient lava flows. Its gravity causes most of Earth's ocean tides, and its presence helps stabilize Earth's rotation over long periods.
Europa
Europa's surface is young, bright, and crossed by dark fractures. Measurements from spacecraft suggest a salty liquid-water ocean may exist below the ice. That makes Europa a major target in the search for environments that could potentially support life.
Ganymede
Ganymede is larger than Mercury and is the only moon known to generate its own internal magnetic field. Its surface contains both dark, heavily cratered terrain and lighter grooved regions.
Io
Jupiter's powerful gravity stretches Io as it orbits, creating intense internal heating. Volcanoes can send material hundreds of kilometers above the surface. Sulfur compounds help create Io's yellow, orange, red, black, and white colors.
Titan
Saturn's largest moon has an atmosphere mostly made of nitrogen. Liquid methane and ethane form lakes, rivers, clouds, and rain, creating a weather cycle that is chemically very different from Earth's water cycle.
Enceladus
Cassini flew through material erupting from Enceladus and detected water, salts, organic molecules, and other compounds. Evidence points to a liquid ocean under the ice and hydrothermal activity on the ocean floor.
Phobos
Phobos is only about 22 kilometers across at its widest scale and is dominated by the large Stickney crater. It slowly spirals closer to Mars and, far in the future, may break apart or collide with the planet.
Moon Systems
Jupiter, Saturn, Uranus, and Neptune each have complex satellite systems. Some moons likely formed around their planets, while others may be captured objects. New small moons continue to be discovered as telescopes and surveys improve.