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Solar system
Dwarf planet, Pluto

About the same age as the Sun: 4.5 billion years


Solar system, Kuiper Belt region

Avg. distance from the Sun

5,914,000,000 km (3,674,000,000 miles)


2,370 km (1,473 miles)


1.27 x 1022 kg

Orbital period around the Sun

247.7 Earth years (90,410 Earth days)

Number of moons

Five: Charon, discovered in 1978, is Pluto's largest moon. Charon's diameter is about half that of Pluto's, leading many to consider Pluto/Charon to be a binary system. In 2006, two smaller moons, Nix and Hydra, were discovered by the Hubble Space Telescope. Hubble observations also uncovered the moons Kerberos in 2011 and Styx in 2012.

Distinguishing features

Pluto was the smallest planet until August 2006, when the International Astronomical Union reclassified it as a dwarf planet. It is the largest dwarf planet known.

Pluto is composed of a large rocky core wrapped in thick layers of ices. Its icy surface and extremely thin atmosphere are predominantly composed of nitrogen with small amounts of methane and carbon monoxide. The terrain shows remarkable variation including dark/bright regions and smooth/mountainous areas. The atmosphere is hazy and extended enough that it is continually being lost into space through interaction with the solar wind.

Pluto’s orbit is more elliptical and more inclined than the orbits of the eight solar system planets. The key reason it is no longer considered a planet is that it is one among thousands to millions of other objects orbiting within the Kuiper Belt region.  Also, the icy dwarf planet is not massive enough to clear debris from its orbit.

One of the images of Pluto obtained by the New Horizons spacecraft, in mid-2015.

Enlarge Image


"Fast Facts: Dwarf planet, Pluto" is a table that lists Pluto's age, location, average distance from the Sun, diameter, mass, orbital period around the Sun, number of moons, and distinguishing features. The text touches upon some of the issues surrounding whether Pluto should be considered a planet. An image of Pluto obtained by the New Horizons spacecraft is included.

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Adaptable, at teacher's discretion
How to use in the classroom

Use this resource as:

A source of information. Read the table to find out about this object.

A reading activity. Give each student a planet-themed Fast Facts table. Ask students to locate specific object characteristics, such as the number of moons or the diameters of their respective planets.

A large-number recognition and ordering activity. Have students review several planet Fast Fact tables, including this one. Have students read the tables to find each planet's distance from the Sun. Then ask them to arrange the planets according to their distance from the Sun, from closest to farthest. Students also can arrange the planets according to their mass and/or diameter, from smallest to largest.

A unit conversion activity. Have students change the distances in either kilometers or miles into astronomical units. One astronomical unit (AU) is the average distance from Earth to the Sun, which equals 149,600,000 km, or 92,960,000 miles.

A compare/contrast activity. Have students review several Fast Facts tables for planets. Students match the planets to statements that describe a unique feature of each planet, such as: This planet is closest to the sun, or this is the largest known dwarf planet. Either the teacher or the students can generate the statements using information from the Fast Facts. Students also can create graphic organizers comparing the features of planets and dwarf planets.

An inquiry tool. Have students write down questions they would like answered about the image and the information in the Fast Facts table.

An engagement tool. Involve students in a discussion.

A critical thinking activity. This Fast Facts can be used with question 15 in "Q&A: Our solar system" to decide whether Pluto should be classified as a dwarf planet or a major planet. After students have read question 15 and the Fast Facts: Dwarf planet, Pluto table, they can compose an essay explaining whether they think Pluto should remain a dwarf planet or be reclassified as a major planet. Students should support their choice with evidence.

Related materials

Amazing Space resources by topic: Solar system

HubbleSite: Press releases on Pluto