The Basics

Just the Pluto/Charon Facts

Average Distance from Sun 39.482 AU
5.9 billion km
3.7 billion miles
Minimum Distance from Sun 29.658 AU
4.4 billion km
2.8 billion miles
Maximum Distance from Sun 49.305 AU
7.4 billion km
4.6 billion miles

Orbit period around Sun

248 years
Surface temperature

-396 to -360 Fahrenheit
-238 to -218 Celsius
35-55 Kelvin

  Pluto Charon
Radius 1,140-1200 km
680-720 miles
603.6 +- 1.4 km
375 +- 1 miles
Mass 1.3 x 1022 kg
0.153 x 1022 kg
Density 1.8 - 2.1 gm/cm3
about twice density of water
1.66 +- 0.01 gm/cm3
Surface composition Frozen water, nitrogen, methane, carbon monoxide Water ice
Atmospheric composition nitrogen, methane, carbon monoxide No detectable atmosphere
Spin period 6.39 days 6.39 days
Orbital period
around Pluto
  6.39 days

The Family of Planets

the planets at a glance

The planets of the solar system are shown in sequence and in relative size (but not to scale in terms of their true separation from one another). Pluto is about 5.5 times smaller than Earth, or about two-thirds the diameter of the Moon. Side by side, Pluto and Charon would barely span the United States.

pluto and charon

The next-largest objects in Pluto's Kuiper Belt neighborhood – at least among the objects we've discovered so far – are Eris and Makemake. Here's a look at relative sizes of known small planets in the Kuiper Belt and Asteroid Belt.

pluto, comet halley, quaoar, sedna, moon, and earth

Pluto's Gravity

A person on Pluto would weigh 1/15 of what they weigh on Earth — a nice way to lose weight, but a chilly way to do it! For comparison, the astronauts walking on the Moon weighed 1/6 of their Earth weight.

Gravity on Pluto
Since the mass of Pluto is 1/455 that of Earth, you might guess that the gravity would be 455 times less. But also take into account that Pluto is 5.5 times smaller than Earth, so someone on Pluto's surface would be 5.5 times closer to the planet's center of mass. Since the force of gravity decreases with the square of the distance from the center of mass, the gravity on Pluto will be changed by a total of (5.5 x 5.5) / 455, equals to 0.07 or 1/15.

Orientation of Pluto and Charon

Orientation of Pluto and Charon

Most planets have poles that point roughly up and out of their orbit planes — the exceptions are Uranus and Pluto, which effectively rotate on their sides. Like most satellites, Charon orbits around Pluto's equator.

Click here for a discussion of how this unusual orientation of Pluto and Charon produced mutual eclipses.

orbits down

Pluto's Orbit Around the Sun

Pluto's orbit is less circular - more elliptical or "egg-shaped" - than those of the other planets. Pluto's 248-year-long orbit has an eccentricity of 0.25, which means that Pluto's distance from the Sun is as little as 29.7 astronomical units (temporarily bringing it closer than Neptune) and as great as 49.3 astronomical units. For about 20 years in each orbit, Pluto is actually closer to the Sun than Neptune.

Most of the planets orbit the Sun close to the same plane (called the ecliptic). Pluto's orbit is tilted (by 17.14 degrees) with respect to this plane, the highest inclination of any planet in the solar system. Mercury's inclination is second highest at 7 degrees. The picture below is a "sideways" view, looking at the solar system from the side and a little above the ecliptic plane.


Spin-Phase Lock

Pluto and Charon both spin and orbit every 6.4 days. The animation illustrates the effect this has by putting people on Pluto and Charon and imagining what they would see in the sky. The "blue" people would see the other object up in the same place in the sky all the time. The "red" people would never see the other object – so if you are on Pluto you would not know Charon is there. And if you were on Charon, you would not see Pluto.

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