Space and Time
Size: Diameter 2300km
Mass: 1.32x10(exp22)kg
Composition: Unknown
Mean temperature: -220°c
Distance from Sun: 5915 million km
Atmosphere/weather: Very thin nitrogen
Moon/satellites: One
Orbital length: 90,589 days
Length of day: 16 hours 7 minutes
Distance from Earth: Max 7525 million km, min 4275 million km
Pluto is the farthest planet from the Sun (usually) and by far the smallest. Pluto is smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton).
Pluto may also be the largest of a group of objects that orbit in a disk-like zone beyond the orbit of Neptune called the Kuiper Belt. This distant region consists of thousands of miniature icy worlds with diameters of at least 1,000km. It is also believed to be the source of some comets.
Discovered by American astronomer Clyde Tombaugh in 1930, Pluto takes 248 years to orbit the Sun. Pluto's most recent close approach to the Sun was in 1989. Between 1979 and 1999, Pluto's highly elliptical orbit brought it closer to the Sun than Neptune, providing rare opportunities to study this small, cold, distant world and its companion moon, Charon. Most of what we know about Pluto we have learned since the late 1970s from Earth-based observations, the Infrared Astronomical Satellite (IRAS), and the Hubble Space Telescope. Many of the key questions about Pluto, Charon and the outer fringes of our solar system await close-up observations by a robotic space flight mission. Pluto and Charon orbit the Sun in a region where there may be a population of hundreds or thousands of similar bodies that were formed early in solar system history. These objects are referred to interchangeably as trans-Neptunian objects, Edgeworth-Kuiper Disk objects or ice dwarves. |
A view of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope. The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 4.4 billion km from Earth.
Pluto is about two-thirds the diameter of Earth's Moon and may have a rocky core surrounded by a mantle of water ice. Due to its lower density, its mass is about one-sixth that of the Moon. Pluto appears to have a bright layer of frozen methane, nitrogen and carbon monoxide on its surface. When it is close to the Sun, these ices thaw, rise and temporarily form a thin atmosphere, with a pressure one one-millionth that of Earth's atmosphere. Pluto's low gravity (about 6 percent of Earth's) causes the atmosphere to be much more extended in altitude than our planet's. Because Pluto's orbit is so elliptical, Pluto grows much colder during the part of each orbit when it is travelling away from the Sun. During this time, most of the planet's atmosphere freezes.
The Hubble Space Telescope mapped the surface of the planet and this rotating movie showing the surface of Pluto was produced from the data. Courtesy of the Hubble Space Telescope Science Institute and the Associated Universities for Research in Astronomy under contract to NASA. Original videos may be found at the Space Telescope Science Institute.
American astronomers James Christy and Robert Harrington discovered Charon in 1978. Charon is almost half the size of Pluto and shares the same orbit. Pluto and Charon are thus essentially a double planet. Charon's surface is covered with dirty water ice and doesn't reflect as much light as Pluto's surface.
In Roman mythology, Pluto (in Greek mythology called Hades) is the god of the underworld. The planet received this name perhaps because it's so far from the Sun that it is in perpetual darkness. Venetia Burney, an eleven year-old girl from Oxford, England, suggested the name.
Images, information and videos courtesy of NASA.