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Solar System Planets Guide: Size, Distance, and Moons

The eight planets of our solar system, from the scorched surface of Mercury to the icy winds of Neptune, at a glance.

Mercury and Venus β€” the two moonless inner planets

Mercury (diameter about 4,880 km) is the smallest planet and closest to the Sun at roughly 58 million km, with a day lasting 59 Earth days and a year of just 88 Earth days. Venus (diameter about 12,100 km) is Earth-sized but has a thick carbon dioxide atmosphere that traps heat, making it the hottest planet even though Mercury sits closer to the Sun; it rotates backward, and its day (243 Earth days) is actually longer than its year (225 Earth days). Neither planet has any moons.

Earth β€” the only known life-bearing planet

Diameter about 12,742 km, orbiting the Sun at roughly 150 million km (the distance defined as 1 astronomical unit). One rotation takes 24 hours and one orbit takes about 365.25 days. Has 1 moon, and is the only planet known to support life.

Mars β€” the Red Planet

Diameter about 6,780 km, colored by iron oxide (rust) on its surface. A day on Mars is close to Earth's at about 24.6 hours, but a year takes roughly 687 Earth days. Has 2 small moons, Phobos and Deimos, and hosts Olympus Mons, the largest known volcano in the solar system.

Jupiter β€” largest planet

A gas giant with a diameter of about 139,800 km, more than 11 times Earth's. Despite its size, it rotates fastest of any planet, completing a day in under 10 hours, while a year takes about 12 Earth years. Has at least 95 known moons, including the four large Galilean moons.

Saturn β€” the ringed planet

Best known for its spectacular ring system made of ice and rock particles. Diameter about 116,500 km, with a day of about 10.7 hours and a year of roughly 29 Earth years. Has at least 146 known moons, including Titan, the second-largest moon in the solar system.

Uranus and Neptune β€” the ice giants

Uranus (diameter about 50,700 km) is uniquely tilted on its side at roughly 98 degrees, so it essentially rolls along its orbit; a year there takes about 84 Earth years, and it has 28 known moons. Neptune (diameter about 49,200 km), the farthest planet at about 4.5 billion km from the Sun, takes roughly 165 Earth years to orbit and hosts the fastest sustained winds in the solar system, over 2,000 km/h, with 16 known moons including the backward-orbiting Triton.

Why "day length" and "year length" do not scale together

A planet's day is determined by how fast it spins on its axis, while its year is determined by how far it orbits from the Sun and how fast it travels β€” two largely independent factors. This is why Venus has a day longer than its year, and why Jupiter, despite taking 12 Earth years to orbit the Sun, spins so fast that its "day" is under 10 hours β€” rotation speed and orbital distance are not linked by any simple rule.

Terrestrial planets vs. gas giants

The inner four planets (Mercury, Venus, Earth, Mars) are relatively small, dense, and rocky, while the outer four (Jupiter, Saturn, Uranus, Neptune) are much larger and made primarily of gas and ice with no solid surface to stand on. This split is thought to result from how the early solar system formed: rocky material could only condense close to the Sun's heat, while gas and ice could accumulate into giant planets farther out.

Frequently Asked Questions

Why isn't Pluto included in this list?

Pluto was reclassified from a planet to a "dwarf planet" by the International Astronomical Union in 2006, based on a new formal definition of "planet" that requires an object to have cleared its orbital neighborhood of other debris, which Pluto has not done.

Which planet is closest to Earth on average?

Despite Mars often being described as our "neighbor," recent calculations based on average orbital positions over time show Mercury is actually the closest planet to Earth on average, since Venus and Mars are each closest only during specific alignments.