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Is Pluto a purple planet?

Pluto was discovered in 1930 and originally classified as the ninth planet in our solar system. However, in 2006, the International Astronomical Union (IAU) reclassified Pluto as a dwarf planet. This has sparked an ongoing debate about whether Pluto should be considered a full-fledged planet or not. In this article, we’ll examine the evidence surrounding Pluto’s status and coloring to try to determine if it can rightly be called a purple planet.

Pluto’s Planet Status

For 76 years after its discovery, Pluto was considered the ninth planet from the Sun. But in 2006, the IAU created a new classification system that demoted Pluto to a “dwarf planet.” Their reasoning was based on several factors:

  • Pluto is small: At just 1,400 miles wide, it is considerably smaller than the other planets.
  • Pluto has an unusual orbit: It is very elliptical and inclined compared to the planets.
  • Pluto is just one of many small icy objects beyond Neptune in a region known as the Kuiper Belt.

Under the new IAU definition, for an object to be classified as a full planet, it must meet three criteria:

  1. It orbits the Sun.
  2. It has sufficient mass and gravity to assume a nearly round shape.
  3. It has “cleared its neighborhood” or orbit of other objects.

While Pluto meets the first two conditions, it does not meet the third since it shares its orbital space with all the other Kuiper Belt objects. Based on this, the IAU decided Pluto did not qualify as a full-fledged planet. This remains a controversial decision, however, and many astronomers still argue in favor of Pluto’s planethood today.

Evidence Supporting Pluto as a Planet

Here are some of the major reasons why Pluto should be considered a planet, according to its supporters:

  • History and cultural significance – Pluto has been considered a planet for over 75 years. It holds an important place in popular culture and the public imagination.
  • Geophysical complexity – Pluto has an atmosphere, weather, seasons, and other complex geophysical processes like the 8 major planets.
  • Orbital dynamics – Unlike most Kuiper Belt objects, Pluto’s orbit is relatively circular and orbits the Sun on the same plane as the other planets.
  • Size and mass – While small, Pluto is significantly larger and more massive than most asteroids, comets, and other minor bodies in the solar system.

Many astronomers argue these qualities make Pluto deserving of planetary status despite its small size. Public opinion polls also tend to favor Pluto’s reinstatement as a planet.

Evidence Against Pluto as a Planet

However, there are still good scientific reasons for classifying Pluto as a dwarf planet rather than a full-scale one:

  • Small size – Pluto is only about 18% the mass of Earth’s Moon and less than 1/5 the mass of Mercury, the smallest official planet.
  • Icy composition – Pluto is composed mostly of ice, unlike the rocky terrestrial planets and gas giants.
  • Non-dominance of its orbit – Pluto shares its orbital neighborhood with thousands of other Kuiper Belt objects of similar size.
  • Irregular orbital parameters – Its orbit is the most inclined and eccentric of any planet.

Based on these characteristics, many astronomers argue that Pluto fits the definition of a dwarf planet better than that of a full-sized one.

What Color is Pluto?

So that covers the debate around Pluto’s status as a planet. But what about its color? Could Pluto actually be a purple planet as the title of this article asks?

Pluto’s surface composition provides clues about its coloring:

  • Nitrogen ice – Nitrogen ice on the surface appears white or transparent.
  • Methane ice – Frozen methane has a reddish hue.
  • Carbon monoxide ice – Carbon monoxide ice is grayish-black.

When these ices are mixed together, especially the methane and nitrogen ice, they take on a color resembling reddish-brown. So from a distance, Pluto does appear to be somewhat reddish or brown in color. But it is not actually purple.

Ice Type Color
Nitrogen ice White/transparent
Methane ice Reddish
Carbon monoxide ice Grayish-black

However, some regions on Pluto do appear more purple or pinkish in enhanced color images captured by the New Horizons spacecraft during its 2015 flyby. These purple-colored areas are believed to contain exposed water ice or complex organic compounds called tholins which tend to be reddish-purple in color.

So in summary, while Pluto may have some small regions that are purple-ish, the overall dominant color of its surface is a reddish-brown. Pluto also lacks a true atmosphere that could create a purple atmospheric haze. So most astronomers would agree it does not qualify as a truly purple planet.


Based on the evidence, Pluto is likely not a purple planet as it is often depicted as reddish-brown due to its surface tholins and ices. While it has some purplish regions and a complex geology, Pluto is still best classified as a dwarf planet rather than a full-sized planet. Its small size, icy composition, non-dominance in its orbit, and irregular orbital parameters compared to the major planets all support its dwarf planet status.

The debate over Pluto’s planethood and colors continues among astronomers. But the flyby of the New Horizons spacecraft helped shed some light by giving us our first close-up, detailed images of Pluto’s surface. This revealed a geologically active world with an intriguing coloring that doesn’t quite live up to the “purple planet” moniker but is unique in our solar system nonetheless.