Daniel Gray

The Giant Impact Hypothesis: Formation of the Moon and Recent Advances in Modeling How did our Moon form? The answer involves a cataclysmic collision between a young Earth and a Mars-sized protoplanet...

Ariel: The Youngest of Uranus's Major Moons Ariel is the fourth-largest of Uranus's five major moons and has the youngest, most geologically active surface of the group. The moon is crisscrossed by ex...

Callisto: The Ancient, Distant Moon of Jupiter Callisto is the outermost of Jupiter's four large Galilean moons and the most heavily cratered object in the solar system. Its ancient, unchanged surface...

Cassini-Huygens: Exploring Saturn and Its Moons The Cassini-Huygens mission was one of the most ambitious and successful planetary exploration missions ever undertaken. Launched in 1997, the Cassini s...

Deimos: Mars's Distant, Peaceful Moon Deimos is the smaller and more distant of Mars's two moons, orbiting at 23,460 km from the planet's surface. Unlike its companion Phobos, which is doomed to destr...

Dione: The Wispy Moon of Saturn Dione is one of Saturn's mid-sized moons, notable for its "wispy terrain"—bright, linear features that crisscross parts of its surface. These features, discovered by Vo...

Earth: The Pale Blue Dot and Our Home in the Cosmos Earth is the only known planet to harbor life, a distinction that makes it unique among the billions of worlds in our galaxy. This uniqueness arises...

Enceladus: The Geyser Moon and Ocean World Enceladus is one of Saturn's most fascinating moons—a small, icy world with geysers erupting from its south pole, revealing a global subsurface ocean beneath...

Europa: An Ocean World in the Outer Solar System Beneath Europa's icy surface lies a global ocean—possibly twice the volume of Earth's oceans—making this Jovian moon one of the most promising places t...

Ganymede: The Solar System's Largest Moon Ganymede is not just Jupiter's largest moon—it's the largest moon in the entire solar system, larger than Mercury and the only moon known to have its own magn...

Giovanni Domenico Cassini: Pioneer of Planetary Astronomy Giovanni Domenico Cassini (1625-1712) was an Italian-French astronomer who made fundamental discoveries about the solar system in the 17th cen...

Hyperion: The Sponge Moon of Saturn Hyperion is one of Saturn's most unusual moons—an irregular, potato-shaped object with a sponge-like appearance created by numerous deep, dark craters. The moon has...

Iapetus: The Two-Tone Moon with a Mysterious Ridge Iapetus is one of Saturn's most distinctive moons, famous for its two-tone coloration—one hemisphere is dark as coal while the other is bright as sno...

Io: The Volcanic Moon of Jupiter Io is the most volcanically active body in the solar system, with hundreds of active volcanoes constantly reshaping its surface. This extreme activity is driven by tid...

Jupiter: The King of Planets and Guardian of the Inner Solar System Jupiter is the largest planet in the solar system, a gas giant so massive that it contains more than twice the mass of all other pla...

Mars: The Red Planet and the Search for Life Mars has captured human imagination for centuries, and today it's the primary target in the search for life beyond Earth. While Mars is currently cold and ...

Mercury: The Extreme World at the Edge of the Sun Mercury is the smallest planet in the solar system and the closest to the Sun, orbiting at an average distance of just 0.39 astronomical units. Despit...

Mimas: The Death Star Moon Mimas is one of Saturn's inner moons, famous for its massive Herschel crater that makes it resemble the Death Star from Star Wars. The crater, which is 130 km across—nearly ...

Miranda: The Jigsaw Puzzle Moon Miranda is the smallest and innermost of Uranus's five major moons, but it has the most extreme and varied topography in the solar system. The moon's surface is a chaot...

The Moon: Earth's Companion and Gateway to the Cosmos The Moon is Earth's only natural satellite and the largest moon relative to its planet in the solar system. Its presence has shaped Earth in profo...

Neptune: The Windy Blue Giant at the Edge Neptune is the farthest planet from the Sun and the windiest world in the solar system, with winds reaching speeds of 2,100 km/h (580 m/s)—nearly supersonic. ...

Nereid: Neptune's Distant, Eccentric Moon Nereid is Neptune's third-largest moon and has the most eccentric orbit of any moon in the solar system, ranging from 1.4 to 9.7 million kilometers from Neptu...

Oberon: The Outermost Major Moon of Uranus Oberon is the second-largest and outermost of Uranus's five major moons, with a radius of 761 km. The moon has a heavily cratered, ancient surface that shows...

Phobos: Mars's Doomed Moon Phobos is the larger and closer of Mars's two small moons, orbiting just 6,000 km above the Martian surface—closer than any other moon to its planet. This proximity means Ph...

Rhea: Saturn's Second Largest Moon Rhea is Saturn's second-largest moon after Titan, with a radius of 764 km. The moon has a heavily cratered, ancient surface that shows no signs of recent geological ...

Saturn: The Ringed Jewel of the Solar System Saturn is instantly recognizable by its spectacular ring system—the most extensive and visible in the solar system. These rings, composed of countless ice ...

The Sun: Our Star and the Engine of the Solar System The Sun is the heart of our solar system—a massive, luminous sphere of plasma that has burned for 4.6 billion years and will continue for billions ...

Tethys: The Icy Moon with a Giant Crater Tethys is one of Saturn's mid-sized moons, notable for its massive Odysseus Crater and the giant canyon Ithaca Chasma that stretches three-quarters of the way ...

Titan: Saturn's Moon with Lakes and Seas !../../images/exposing-titan-surface-41e1f0.jpg Titan is unique in the solar system: the only moon with a thick atmosphere and the only world besides Earth wit...

Titania: The Largest Moon of Uranus Titania is the largest of Uranus's five major moons, with a radius of 788 km. The moon has a mix of ancient, heavily cratered terrain and younger regions with exten...

Triton: Neptune's Captured Moon with Geysers Triton is Neptune's largest moon and one of the most fascinating worlds in the outer solar system. The moon orbits retrograde (backward), indicating it was...

Umbriel: The Darkest of Uranus's Major Moons Umbriel is the third-largest of Uranus's five major moons and the darkest, with an albedo of only 0.19. The moon has a heavily cratered, ancient surface th...

Uranus: The Tilted Ice Giant Uranus is unique among the planets: it rotates on its side, with an axial tilt of 98 degrees that creates extreme seasonal variations unlike any other planet. This unusual...

Venus: The Hellish World Behind the Veil Venus is often called Earth's twin due to its similar size and mass, but the two planets could not be more different. While Earth is a haven for life, Venus is...

Solar System Exploration Explore our solar system in 3D. Click on planets and moons to view articles about them. Use the date selector to see planetary positions at different times, and adjust the tim...