Planets in Our Solar System: 8 Official Worlds in Order

There’s a peculiar thing about knowing something since childhood — you don’t question it until someone else does. Ask most adults how many planets orbit the Sun, and a brief hesitation usually follows. That pause matters because the answer changed in 2006. The International Astronomical Union redefined what makes a planet, and suddenly the solar system had one fewer world. Here’s everything you actually need to know about the eight planets, in order, and why it still matters.

Number of planets: 8 · Largest planet: Jupiter · Planet with rings: Saturn (most prominent) · Former planet: Pluto (now dwarf) · Closest to Sun: Mercury

Eight worlds orbit the Sun in a well-ordered sequence, each distinct in character and history.

What are the 8 planets and describe each in order?

When astronomers list planets in order from the Sun, they begin with Mercury and end with Neptune — eight worlds sorted by their orbital distance. This ordering isn’t arbitrary; it reflects the solar system’s formation history and each planet’s distinct environment.

Mercury

• Closest planet to the Sun
• Smallest of the eight planets
• No substantial atmosphere, extreme temperature swings

Venus

• Second planet from the Sun
• Hottest surface of any planet due to greenhouse effect
• Similar size to Earth, fundamentally different conditions

Earth

• Third planet from the Sun
• Only known world with liquid surface water and life
• Single large natural satellite: the Moon

Mars

• Fourth planet from the Sun
• Called the Red Planet for iron oxide on its surface
• Has two small moons: Phobos and Deimos

Jupiter

• Fifth planet from the Sun
• Largest planet in the solar system
• Gas giant with at least 95 known moons

Saturn

• Sixth planet from the Sun
• Most prominent ring system of any planet
• Second-largest planet with at least 146 known moons

Uranus

• Seventh planet from the Sun
• Tilted axis by roughly 98 degrees, orbiting on its side
• Coldest atmosphere among the gas giants

Neptune

• Eighth and farthest known planet from the Sun
• Strongest sustained winds in the solar system
• Orbital period of approximately 165 Earth years

Why is Pluto no longer a planet?

The question of Pluto’s status cuts deeper than most people expect — it involves a definition fight that split the scientific community and raised fundamental questions about what makes a planet a planet.

In August 2006, the International Astronomical Union established three criteria for full planet status: an object must orbit the Sun, have sufficient mass for gravity to create a nearly round shape, and have cleared the neighborhood around its orbit of other debris.

— International Astronomical Union

IAU definition of planet

Pluto met the first two conditions but failed the third — its orbital zone overlaps with the Kuiper Belt, a region of icy objects beyond Neptune (NASA Science).

Pluto as dwarf planet

The IAU created a new category called “dwarf planets” for objects that meet the first two criteria but have not cleared their orbital neighborhoods. This placed Pluto, along with Eris, Haumea, Makemake, and Ceres, into a separate class. Pluto is smaller than Earth’s Moon and orbits in a region where Neptune’s gravity influences its path (Space.com).

Discovery and naming

Clyde Tombaugh discovered Pluto in 1930 at the Lowell Observatory in Arizona. An 11-year-old girl named Venetia Burney in England suggested the name to her grandfather, who passed it to Lowell Observatory. The name honored the Roman god of the underworld and fit the tradition of naming planets after mythological deities (Space.com).

When Clyde Tombaugh discovered a ninth planet in 1930, the Lowell Observatory received naming suggestions from the public. Venetia Burney, an 11-year-old schoolgirl in England, suggested the name Pluto after the Roman god of the underworld.

— Venetia Burney’s family account

Why isn’t our Moon considered a planet?

This question trips up many people because the Moon shares key features with planets — it’s large relative to Earth, spherical from its own gravity, and made of rocky material. Yet astronomical classification depends on orbital behavior, not physical characteristics alone.

Planet criteria

A true planet must orbit the Sun directly, not another planet. The Moon fails this criterion because it orbits Earth, which itself orbits the Sun. The Moon is gravitationally bound to Earth and travels with it through space, but follows a path that curves around Earth’s center rather than the Sun’s (Royal Observatory Greenwich).

Moon’s orbit around Earth

The Moon completes one orbit around Earth in approximately 27.3 days, which defines our lunar month. During this orbit, it follows a path controlled primarily by Earth’s gravity. Even though the Moon travels around the Sun as part of the Earth-Moon system, its motion relative to the Sun never creates a direct heliocentric orbit — it never “falls” directly toward the Sun in the way planets do.

What are the dwarf planets in our solar system?

Dwarf planets occupy a middle ground — large enough for gravity to shape them into spheres, but not dominant enough in their orbits to clear away neighboring objects. The IAU officially recognizes five, though the door remains open for more.

Pluto

Pluto remains the most famous dwarf planet, discovered in 1930 and reclassified in 2006. It has five known moons, a nitrogen-methane atmosphere, and a heart-shaped nitrogen ice plain called Sputnik Planitia. Its orbital period spans 248 Earth years, and it crosses Neptune’s orbital path during part of each circuit (Space.com).

Ceres

Ceres sits in the asteroid belt between Mars and Jupiter, making it the only dwarf planet in the inner solar system. NASA’s Dawn mission visited Ceres in 2015, becoming the first spacecraft to orbit a dwarf planet. Ceres is the smallest recognized dwarf planet and was the first asteroid discovered, initially classified as a planet before more asteroids were found nearby.

Eris

Eris orbits in the scattered disc region beyond the Kuiper Belt and was discovered in 2005. It is nearly the same size as Pluto and was actually the trigger for the IAU’s definition debate — its discovery suggested there might be many more large objects waiting to be found, forcing astronomers to decide what “planet” really means.

Others

Haumea and Makemake round out the five recognized dwarf planets. Both orbit in the Kuiper Belt region. Haumea has an elongated shape and at least two moons, while Makemake has one known moon. Astronomers expect more than a hundred candidate objects could eventually qualify as dwarf planets as surveys improve (NASA Science).

Which planet has 42 years?

Uranus completes one orbit around the Sun in roughly 84 Earth years, so one Uranian year spans more than eight decades of human life. The “42 years” reference typically relates to specific orbital positions or observational windows rather than a single orbital period.

Uranus rotation and orbit facts

Uranus rotates on its axis in approximately 17 hours, yet the planet’s extreme axial tilt — roughly 98 degrees from vertical — means that each pole experiences 42 years of continuous sunlight followed by 42 years of darkness. This occurs because Uranus effectively rolls around the Sun on its side. Its atmosphere reaches temperatures of -224 degrees Celsius, making it the coldest planetary atmosphere in the solar system (Space.com).

Related reading: planets order from the Sun · dwarf planets like Ceres

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