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Pluto is the ninth and usually the farthest planet from the sun in our solar system. It also the
smallest planet in our solar system and the last to be discovered. It is smaller than a lot of the
other planets' moons, including our moon. Pluto is the only planet in our solar system that
has not been visited by our spacecraft yet. We only have blurry pictures of its surface; even
the Hubble space telescope orbiting the Earth can only get grainy photos because Pluto is so
far from us.
SIZE
Pluto is about 1,429 miles (2300 km) in diameter. This is about 1/5 the diameter of the
Earth.
Pluto is the smallest planet in our Solar System.
MASS AND GRAVITY
Pluto's mass is about 1.29 x 1022 kg. This is about 1/500th of the mass of the Earth. The
gravity on Pluto is 8% of the gravity on Earth.
Pluto is the least massive planet in our Solar System
A 100 pound person on Pluto would weigh only 8 pounds.
LENGTH OF A DAY AND YEAR ON PLUTO
Each day on Pluto takes 6.39 Earth days. Each year on Pluto takes 247.7 Earth years (that
is, it takes 247.7 Earth years for Pluto to orbit the sun once).
PLUTO'S ORBIT
Pluto is 39 times farther from than the sun than the Earth is. Pluto ranges from 2.8 to 4.6
billion miles (4.447 billion to 7.38 billion km) from the Sun. From Pluto, the sun would
look like a tiny dot in the sky.
Occasionally, Neptune's orbit is actually outside that of Pluto; this is because of Pluto's
highly eccentric (non-circular) orbit. During this time (20 years out of every 248 Earth
years), Neptune is actually the farthest planet from the Sun not Pluto. From January 21,
1979 until February 11, 1999, Pluto was inside the orbit of Neptune. Now and until
September 2226, Pluto is outside the orbit of Neptune.
Orbital Eccentricity
Pluto has a very eccentric orbit; that means that its distance from the sun varies a lot during
its orbit around the sun. Sometimes it is even closer to the sun than the planet Neptune (it
was that way from January 1979 to February 11, 1999)! Pluto also rotates about its axis in
the opposite direction from most of the other planets.
Orbital Inclination
Pluto's orbit is tilted from the plane of the ecliptic. This angle, its orbital inclination, is
17.15°. This is the largest inclination of any of the planets.
TEMPERATURE ON PLUTO
Pluto is VERY, VERY cold. Its temperature may range from between -396°F to -378°F
(-238°C to -228°C, or 35 K to 45 K). The average temperature is -393°F (-236°C = 37 K).
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