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Pluto – Dwarf planet · Kuiper Belt
Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Inst · Public domain
🪨 Dwarf planets · The Little Worlds

Pluto

Dwarf planet · Kuiper Belt

Pluto is a small icy world in the Kuiper Belt, a zone of frozen objects beyond Neptune. It has mountains of water ice, glaciers of frozen nitrogen, a thin blue atmosphere, and a giant heart-shaped plain.

  • 2,377 kmYou could line up 5 of them across Earth.
  • 248 yearsYear
  • 5 (biggest: Charon)Moons
🔭 Find it in the sky

Take a closer look

A dancing pair

Pluto is smaller than our own Moon – only about two-thirds as wide. Its moon Charon is half Pluto’s width, so instead of Charon simply circling Pluto, the two swing around a point in the space between them, like dancers holding hands. They always keep the same faces turned towards each other.

Noon like twilight

Pluto is so far away that sunlight takes about five and a half hours to get there. At midday, the Sun is only as bright as Earth’s sky shortly after sunset. The ground is around −230 °C, cold enough to freeze the air we breathe solid.

The long trip

New Horizons was launched in 2006 at record speed, passing the Moon’s orbit in just nine hours. Even so, it took nine and a half years to reach Pluto. Because it was so far away, its radio messages were faint and slow, and sending all its pictures home took more than a year.

Size it up

EarthPluto

You could line up 5 of them across Earth. Both are drawn to the same scale.

How we found out

  1. 1930

    Clyde Tombaugh, 24, discovers Pluto at Lowell Observatory by comparing photographs taken nights apart.

  2. 1930

    Venetia Burney, an 11-year-old in Oxford, suggests the name “Pluto”, the Roman god of the underworld.

  3. 1978

    James Christy discovers Pluto’s large moon Charon.

  4. 2006

    The International Astronomical Union reclassifies Pluto as a dwarf planet.

  5. 2015

    New Horizons flies past on 14 July and reveals the famous “heart”. Some of Tombaugh’s ashes are on board.

🤔 Something to wonder about

Should Pluto be a planet?

See it yourself

Very faint – you need a large telescope and a star chart.

Got it?

Mark Pluto as explored to earn 10 XP.