What is the Color of Pluto?

Identification

• Pluto is determined by astronomers to be light brown, on the basis of a low-resolution image they created by tracking brightness changes of Pluto over several years, when it was partially eclipsed from our viewpoint by its moon Charon. They theorize that the color is due to frozen methane deposits on the surface, which are affected by faint sunlight.

Features

• Pluto is made of rock and ice. Scientists theorize that its frozen surface is composed of 98 percent nitrogen, with small amounts of methane and trace amounts of carbon monoxide.

  Pluto is usually further from the sun than any of the planets, but because of its highly elliptical orbit, occasionally it comes closer to the sun than Neptune. It takes 248 years for Pluto to orbit the sun, and it is closer to the sun than Neptune for 20 years at a time. Pluto's rotation period is a little over six days.

Effects

• Besides Charon, discovered in 1978, Pluto has two much smaller moons named Nix and Chara. These moons were discovered from images taken by The Hubble Space Telescope in 2005. Scientists were able to determine from the Hubble images that all three moons are a neutral gray color, similar to Earth's moon. This suggests that those three moons were created by the same event.

  Charon is so large compared to Pluto that some scientists view them as a binary system rather than as a planet and satellite.

Size

• When Pluto was discovered in 1930, it was classified as a planet, but now is considered the largest member of the Kuiper Belt, which is composed of large asteroids in the same region. Pluto was put into a new category called "dwarf planets" devised in 2006 by the International Astronomical Union. Two other objects in the solar system which are in this category are called Eris and Ceres. Eris is actually larger than Pluto.

  The smallest planet besides Pluto is Mercury, and Pluto's mass is 25 times smaller than Mercury's. Pluto is even smaller than Earth's moon.

Expert Insight

• Pluto's demotion from planet to dwarf planet kicked up controversy among professional astronomers, hobbyists and the general public, some of whom staunchly continue to define Pluto as a planet. Alan Stern, a scientist at Southwest Research Institute, was quoted as saying, "The decision stinks." Stern is leader of the New Horizons spacecraft mission to Pluto, a NASA project which had been sent from Earth in January 2006. The re-classification had come after years of debate.

  New Horizons is scheduled to reach its destination in 2015, and once it does, we should finally have good photographs of Pluto--planet or not.