Moons of Pluto
Pluto and Charon: a double world
The dwarf planet Pluto has five moons. The biggest, Charon, is so large compared with Pluto that the two orbit a point in space between them, like a double planet.
NASA/Johns Hopkins APL/Southwest Research Institute, New Horizons (PIA19968), 14 Jul 2015. Public domain.
Meet the moons
Charon
- Diameter
- 1,212 km, half of Pluto
- Discovered
- 1978, James Christy
- One orbit
- 6.4 days
Pluto and Charon are tidally locked to each other: each always shows the same face to the other. From one side of Pluto, Charon hangs motionless in the sky; from the other it is never seen.
When New Horizons flew past on 14 July 2015 it revealed a canyon belt longer than the Grand Canyon and a dark red north pole, nicknamed Mordor Macula. The red comes from methane gas that escapes Pluto, freezes onto Charon's cold pole and is changed by sunlight into reddish compounds.
The little ones
Nix, Hydra, Kerberos and Styx are small, irregular moons a few tens of kilometres across. They tumble chaotically as they orbit the Pluto-Charon pair.
All five probably formed from debris after a collision between Pluto and another Kuiper Belt object, a smaller echo of how our own Moon formed.
Could life be here?
Our rough guide, from 0 (no chance) to 5 (among the best places to look). No life has been found beyond Earth.
Could life be here? Pluto and Charon
- Pluto probably has an ocean beneath its icy heart
- Charon may once have had an ocean that froze
- Charon's ocean is likely frozen solid
- Far from the Sun, with little energy
Verdict: Pluto's hidden ocean is an intriguing maybe; Charon is very unlikely.
Quick answers
Is Charon a moon or a planet?
It is a moon of the dwarf planet Pluto, but it is so large that the pair orbit a point between them, which is why they are often called a double world.
Why is Charon's pole red?
Methane escaping from Pluto freezes onto Charon's cold pole and is changed by sunlight into reddish compounds.
How many moons does Pluto have?
Five: Charon, Nix, Hydra, Kerberos and Styx.
Sources and credits
- NASA Science, Pluto moons.
- NASA/Johns Hopkins APL/SwRI, New Horizons.
- Grundy, W. M. et al. (2016), The formation of Charon's red poles from seasonally cold-trapped volatiles, Nature 539, 65–68.
Photos credited to NASA, NOAA and other public-domain sources are used with thanks; BotBuhdy adds a small botbuhdy.com mark. Pictures labelled AI-generated illustration are artist-style illustrations made for this page, not photographs.