Nine Planets: The Complete Guide to Our Solar System

There are 8 official planets in our solar system as of 2006 — when the IAU redefined “planet” and reclassified Pluto as a dwarf planet. However, many people still search for “nine planets” because Pluto was the ninth planet for 76 years (1930–2006). This page covers both: the current 8 planets and Pluto’s story.

The 8 Planets in Order from the Sun

#	Planet	Type	Distance from Sun	One Year (Earth days)
1	Mercury	Terrestrial	57.9M km	88 days
2	Venus	Terrestrial	108.2M km	225 days
3	Earth	Terrestrial	149.6M km	365 days
4	Mars	Terrestrial	227.9M km	687 days
5	Jupiter	Gas Giant	778.5M km	4,333 days
6	Saturn	Gas Giant	1,432M km	10,759 days
7	Uranus	Ice Giant	2,867M km	30,687 days
8	Neptune	Ice Giant	4,515M km	60,190 days

Why People Say “Nine Planets” — The Pluto Story

Pluto was discovered in 1930 and classified as the ninth planet for 76 years. In 2006, the International Astronomical Union (IAU) formally defined what a planet is for the first time. Under the new definition, a planet must: (1) orbit the Sun, (2) have enough mass to be roughly spherical, and (3) clear the neighborhood around its orbit. Pluto fails the third test — its orbit overlaps with other Kuiper Belt objects. It was reclassified as a dwarf planet alongside Ceres, Eris, Makemake, and Haumea.

So the answer depends on when you went to school. If you learned before 2006: nine planets. After 2006: eight planets. Both answers have a valid reason behind them.

Quick Facts for Each Planet

1. Mercury — Smallest and Fastest

Mercury is the smallest planet and orbits the Sun in just 88 days — faster than any other planet. Despite being the closest to the Sun, it is not the hottest planet. It has almost no atmosphere, so heat escapes at night and temperatures swing from 430°C (day) to −180°C (night).

2. Venus — Hottest Planet

Venus is the hottest planet at 465°C — hotter than Mercury despite being farther from the Sun. Its thick CO₂ atmosphere creates a runaway greenhouse effect. Venus also spins backwards compared to most planets, and a day on Venus is longer than its year.

3. Earth — The Only Known Habitable Planet

Earth is the only planet known to support life. It has liquid water on its surface, a protective magnetic field, and an atmosphere with 21% oxygen. Earth is the densest planet in the solar system and has one natural satellite — the Moon.

4. Mars — The Red Planet

Mars gets its red color from iron oxide (rust) on its surface. It has the tallest volcano in the solar system — Olympus Mons, at 21.9 km — and the longest canyon — Valles Marineris, stretching 4,000 km. Mars has two small moons: Phobos and Deimos.

5. Jupiter — Largest Planet

Jupiter is the largest planet — so massive that all other planets combined would fit inside it twice over. Its Great Red Spot is a storm that has been raging for at least 350 years. Jupiter has 95 known moons, including Europa, which may have a liquid ocean beneath its icy surface.

6. Saturn — Ringed Giant

Saturn’s iconic rings are made of ice and rock, ranging in size from grains of sand to mountains the size of houses. Saturn is the least dense planet in the solar system — it would float on water. It has 146 known moons. Titan, its largest moon, is the only moon in the solar system with a thick atmosphere and liquid lakes on its surface — though those lakes are filled with liquid methane, not water. Saturn’s rings are thought to be geologically young, possibly forming just 100 million years ago — younger than the dinosaurs.

7. Uranus — Tilted Ice Giant

Uranus rotates on its side — its axial tilt is 98°, meaning it essentially rolls around the Sun like a ball. Each pole gets 42 years of continuous sunlight followed by 42 years of darkness. Uranus is the coldest planet in the solar system, reaching −224°C.

8. Neptune — Windiest Planet

Neptune has the strongest winds in the solar system, reaching speeds of 2,100 km/h. It takes 165 Earth years to orbit the Sun once — so Neptune has only completed one full orbit since its discovery in 1846. Its moon Triton orbits backwards and is slowly spiraling inward.

Pluto: The Former Ninth Planet

Even as a dwarf planet, Pluto is fascinating. It has five moons (Charon, Styx, Nix, Kerberos, Hydra), a heart-shaped glacier of nitrogen ice called Tombaugh Regio, and a thin atmosphere that freezes and collapses when Pluto moves far from the Sun. NASA’s New Horizons mission flew past Pluto in 2015, revealing an unexpectedly complex, geologically active world.