Pluto’s orbit is very different from that of the other planets. In fact, in 2006, Pluto was declared by scientists to not be a planet at all, but a dwarf planet, like other small bodies beyond Pluto that are within reach of the Sun’s gravitational pull. Pluto orbits in a highly oval path called an ellipse, which is angled to the other planets’ orbits by about 17.1 degrees. Pluto’s distance from the Sun varies because of this oval path, so that sometimes it is closer to the Sun than Neptune.
In 1976, James Christie discovered Pluto’s moon, Charon. Charon is about half as big as Pluto, which makes Pluto and Charon more like a double planet than a planet and moon.

The basics

Order (outwards from the Sun): 9 or 8
Average distance from the Sun: 5 915 800 000 km (39.55 astronomical units)
Period of revolution (length of year): 248.03 years
Period of rotation (length of day): 6 days 9 hours 17 minutes
Diameter: 2 300 km
Surface gravity: 0.05 times greater than Earth’s
Composition: Probably rock covered with methane ice
Atmosphere: A thin atmosphere of nitrogen, methane, and carbon monoxide that is produced only when Pluto is closest to the Sun
Satellites: 1 moon (Charon, diameter = 1 200 to 1 300 km)
Surface temperature: -215 degrees C

Appearance of surface

Scientists suppose that the rocky surface of Pluto is covered by ice frozen as hard as steel. There are also polar ice caps of frozen methane, which partially melt when Pluto is nearest the Sun, releasing the gas that forms Pluto’s atmosphere.

Appearance in Earth’s sky

Pluto is invisible without a moderate-sized telescope.

Telescopic appearance

Even with the largest telescopes on Earth, Pluto appears as a faint star-like point. No details can be seen at all. The Hubble Space Telescope has been able to resolve some rough details on Pluto’s surface, and also detect its moon, Charon.

Canadian Heritage Information Network
Australian Museums & Galleries Online, Australia; Centre of the Universe; Gemini Observatory, Hawaii; Glenbow Museum; The Manitoba Museum; National Research Council Canada; Planétarium de Montréal

© Canadian Heritage Information Network, 2003

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans