Pluto was discovered in 1930 by a lucky accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway.

• Of all the planets in the Solar System Pluto is the smallest planet.

• It is smaller than Earth’s Moon, and half the width of Jupiter’s moon, Ganymede.

• Pluto moves around the Sun on a diverse plain than the other 8 planets, going over them and below them.

• Pluto’s orbit is oval, which means that it can come closer to the Sun than Neptune, but then go almost two billion kilometers further away from Neptune’s orbit.

• Pluto has one moon, Charon. This moon is not much smaller than Pluto itself. No other moon is as close to the size of its planet as Charon is to Pluto.

• Pluto’s journey around the Sun takes 248 Earth years. This means that, since its discovery in 1930, it still has 177 years to go until it has made a complete orbit around the Sun.

• Pluto is the only planet in the Solar System which has not been explored by any space probe.

• Pluto is the planet with the lowest pull of gravity in the Solar System. This explains why its moon, Charon, moves around the planet so closely.

• A day on Pluto lasts for 6 days and 9 hours, which mean that it has the second slowest speed of rotation in the Solar System.

• No one knows what Pluto’s atmosphere contains, or even if it has an atmosphere. Any atmosphere is most likely to contain nitrogen.