July 12, 2012

Astronomers using the Hubble Space Telescope (HST) have discovered another moon orbiting Pluto, announces NASA. The new satellite is the fifth found circling the small body, which for decades was widely considered the ninth planet in the solar system. Pluto was “demoted” from planet to a new category of space object called “dwarf planet” after astronomers in the 1990′s found many objects similar to Pluto in the outer reaches of the solar system, in an area called the Kuiper Belt. Pluto was discovered by Clyde W. Tombaugh in 1930, based on predictions by astronomer Percival Lowell in 1905. Pluto is 1,460 miles (2,350 kilometers) in diameter.

Pluto is so far from Earth and is so small that even powerful telescopes reveal little detail of its surface. The Hubble Space Telescope gathered the light for the pictures of Pluto shown here. (NASA)

Astronomers with the SETI Institute, a research organization that searches for life in the universe beyond Earth, discovered the new moon and gave it the temporary name P5. The astronomers are using the HST to study Pluto in preparation for a fly-by of the dwarf planet by the New Horizons space probe in July 2015. New Horizons was launched in 2006 to explore Pluto, its largest moon Charon, and other objects in the Kuiper Belt.

According to the researchers, P5 is a tiny, irregularly shaped body that measures from 6 to 15 miles (10 to 25 kilometers) across. The astronomers were unable to get a closer measurement because Pluto and its moons are about 2.8 billion miles (4.7 billion kilometers) away from Earth. Pluto’s moon Charon, which is about 750 miles (1,207 kilometers) in diameter, was discovered in 1978. Hydra and Nix, each up to 100 miles (160 kilometers) in diameter, were found in 2005. Pluto’s fourth moon, P4, discovered in 2011, is about 8 to 21 miles (13 to 34 kilometers) in diameter.

The scientists were a bit disconcerted by the discovery of an unknown moon as New Horizons is nearing Pluto. “All of this stuff poses a navigation hazard for New Horizons,” according to Ray Villard, news director of the Space Telescope Science Institute. However, tiny P5 has also produced a sense of wonder at the complexity of ex-planet Pluto’s system of satellites.

Additional World Book articles:

• Space exploration
• Exploring the Suburban Solar System (a special report)
• Astronomy 1930 (Back in Time article)
• Astronomy 1978 (Back in Time article)
• Astronomy 2006 (Back in Time article)
• Space exploration 2006 (Back in Time article)