Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. After Pluto was discovered in 1930, it was declared to be the ninth planet from the Sun. Beginning in the 1990s, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt and the scattered disc, including the dwarf planet Eris. This led the International Astronomical Union in 2006 to formally define the term planet—excluding Pluto and reclassifying it as a dwarf planet. Pluto is the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris. Like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—one-sixth the mass of the Moon and one-third its volume.

Read more in the app

Scientists Identify a Possible Source for Red Cap on Pluto’s Largest Moon Charon

Pluto's Moon Has a Mysterious Red North Pole, And We May Finally Know Why

Curious Kids: Why does it matter if Pluto is a planet or a dwarf planet?

Pluto’s Mountains, Frozen Plains and Foggy Hazes - from NASA’s New Horizons Space Probe

What's it like to be on Venus or Pluto? We studied their sand dunes and found some clues.

Compare Sand Dunes Across the Solar System, From Venus to Pluto

When will Pluto complete its first orbit since its discovery?

50 years ago, scientists had hints of a planet beyond Pluto

Swirling gas around a young star is giving birth to a far-off planet that's about 9 times the mass of Jupiter and located twice as far from its star as Pluto is from the Sun. The oddly massive but distant world is forcing astronomers to rethink how planets form in the first place.

How Pluto walks a tightrope between a stable and chaotic orbit

Researchers Think They've Cracked The Secret Behind Pluto's Weirdly Unstable Orbit

Pluto’s Orbit is Surprisingly Unstable

Conversation with New Horizons Deputy Project Scientist about the weird cryovolcanoes on Pluto (WeMartians Podcast)

Giant Ice Volcanos on Pluto May Have Formed From Multiple Cryovolcanic Eruption Events

Towering ice volcanoes identified on surprisingly vibrant Pluto

Pluto’s Surface was Shaped by Ice Volcanoes

Pluto’s Hidden Ice Volcanoes Hint at the Possibility of Life. The discovery suggests the dwarf planet may be harboring a subsurface liquid ocean.

Ice volcanoes on Pluto may still be erupting

Enormous Cryovolcanoes Spotted on Pluto

Pluto’s peaks are ice volcanoes, scientists conclude - Existence of volcanoes makes idea that dwarf plant is inert ball of ice look increasingly improbable