Nasa’s New Horizon’s spacecraft has sent back the first close images of Pluto ever (Picture: EPA/NASA)

Pluto was handed its marching papers nine years ago today, when astronomers voted to demote the former ninth planet of the solar system to a dwarf planet.

On that day everything children thought they knew about the solar system was dashed, scissors were taken to thousands of classroom maps of the stars and well-learned mnemonics were rewritten.

Many astronomers said at the time that it was a triumph of science over sentiment.

But if Pluto is more than just a dwarf in your sky, here are 13 amazing facts about the little guy that will blow your mind:


1. When Pluto was discovered in 1930 at the Lowell Observatory, astronomers received suggestions from around the world about what to name it.



The moniker Pluto was put forward by Venetia Burney, an 11-year-old girl from Oxford, who thought the god of the underworld in Greek mythology would be a fitting name for the shadowy and distant planet.

Members of the Lowell Observatory could vote on a shortlist of three names.

These were Venetia’s suggestion, Minerva (which was already the name for an asteroid) and Cronus, which had been put forward by an astronomer no one liked very much.

Venetia earned £5 for her winning entry, around £300 in today’s money.

2. Like Prince, Pluto also has a symbol.

The PL monogram is not only the first two letters in the dwarf planet’s name, it is also the initials of Percival Lowell, the American astronomer who first predicted that Pluto existed.

The Lowell Observatory was also named after him following his theory that a planet would be found in the outer reaches of the solar system because of an unseen gravitational influence on Neptune and Uranus.

3. However, officially, after Pluto’s demotion the former planet is now simply called asteroid number 134340.

New Horizons passes Pluto and its largest moon, Charon (Picture: EPA/NASA/APL/SWRI)

4. Although Pluto was thought to be a planet for 76 years, it is actually only the second most massive of the dwarf planets in the solar system.

Nearby Eris is 27 per cent more massive, although Pluto has greater volume.

It was the discovery of Eris in 2005 that led astronomers to redefine what a planet was, causing Pluto to lose its status the following year.

5. Pluto has five moons, of which Charon is the largest.

Charon’s diameter is over half that of Pluto’s and they are sometimes considered a binary system because their orbits interact with each other.

The other moons are smaller and are called Styx, Nix, Kerberos and Hydra.

6. The dwarf planet is the only one known to have an atmosphere, consisting of nitrogen, methane and carbon monoxide.

It would be toxic for humans to breathe and changes depending on how far Pluto is from the sun.

When its elliptical orbit brings it closer to the sun (perihelion), the atmosphere is gas, but when it travels to the furthest point (aphelion), the gas in the atmosphere freezes and falls like snow.

7. This orbit is so eccentric that at times Pluto is closer to the sun than Neptune.

It was last ‘inside’ Neptune’s orbit in 1999.



8. Pluto has a subsurface ocean of frozen water which is between 100 and 180 kilometres deep.

This means that there is three times more water on the dwarf planet than in all of Earth’s ocean’s combined.

Its remaining two-thirds are made up of a dense core of rock, with a surface of frozen nitrogen.

New Horizons managed to send back detailed images of Pluto’s mountains on the surface (Picture: NASA/AP)

9. Like Venus and Uranus, Pluto has a retrograde rotation, which means it spins in a different direction to Earth.

This rotation means the sun rises in the west and sets in the east.

It does one full rotation every week.

10. It takes about five and a half hours for sunlight to reach Pluto, on average.

This compares to the eight minutes it takes rays to reach us on Earth.

11. This is because Pluto is on average 5.9 billion kilometers (3.6 billion miles) from the sun, compared to our 149.6 million km.

Looking at Pluto from Earth is like trying to see a walnut from 30 miles away.

12. The year that Pluto was demoted, the American Dialect Society voted ‘plutoed’ as its word of the year.

They defined it as ‘to demote or devalue someone or something’.

13. The man who discovered Pluto is about to be the first person whose remains will be sent outside the solar system, on board Nasa’s New Horizons space craft.

Clyde Tombaugh’s ashes were placed in a casket on the probe which flew past the dwarf planet six weeks ago, and sent back incredible pictures to Earth.

It is now carrying on its journey through the Kuiper Belt and out into interstellar space in hope of making contact with life outside the Solar System.


The container holding the eminent astronomer’s ashes bears the inscription: ‘Interred herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system’s ‘third zone’. Adelle and Muron’s boy, Patricia’s husband, Annette and Alden’s father, astronomer, teacher, punster, and friend: Clyde W. Tombaugh (1906-1997)’.

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