Image: Pluto and moons
An image from the Hubble Space Telescope, captured March 2, shows Pluto and its largest moon, Charon, at the center — with two smaller satellites known as P1 and P2 appearing as specks farther out.
updated 3/10/2006 1:24:49 PM ET 2006-03-10T18:24:49

Pluto’s two recently discovered satellites have essentially the same neutral color as Pluto’s large moon, Charon, scientists said Friday.

Charon’s surface is known to consist primarily of water ice, so the similar colors of P1 and P2 suggest that these moons have water ice surfaces, too.

The finding supports the theory that all three of Pluto’s moons were formed from a single giant impact that took place about 4.6 billion years ago. Recent observations about the orbital motions of Pluto’s recently discovered moons, P1 and P2, also support this theory.

"Everything now makes even more sense," said Alan Stern of the Southwest Research Institute. "If all three satellites presumably formed from the same material lofted into orbit around Pluto from a giant impact, you might well expect the surfaces of all three satellites to have similar colors."

Stern, principal investigator for NASA’s New Horizons mission currently headed toward Pluto, and colleague Hal Weaver of Johns Hopkins University’s Applied Physics Laboratory led the research team that identified the color of the distant planet’s newfound moons using the Hubble Space Telescope. The finding was announced earlier this month.

The team found that P1 and P2 have essentially the same color as Charon’s surface. The surfaces of all three moons reflect sunlight with equal efficiency at all wavelengths; this property also applies to Earth’s moon.

Pluto’s surface, in contrast, has a reddish hue, which is believed to be the result of interactions between sunlight and nitrogen and methane surface ices.

The finding was detailed in a recent International Astronomical Union Circular, a scientific newsletter that reports on astronomical discoveries.

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