The team determined that Pluto's two "new" satellites, discovered in May 2005 and provisionally called S/2005 P 1 and S/2005 P 2, have identical colors to one another and are essentially the same, neutral color as Charon, Pluto's large moon discovered in 1978.

All three satellites have surfaces that reflect sunlight with equal efficiency at all wavelengths, which means they have the same color as the Sun or Earth's moon. In contrast, Pluto has more of a reddish hue.

The new observations were obtained March 2 with the high-resolution channel of the Hubble's Advanced Camera for Surveys. The team determined the bodies' colors by comparing the brightness of Pluto and each moon in images taken through a blue filter with those taken through a green/red filter.

"The high quality of the new data leaves little doubt that the hemispheres of P1 and P2 that we observed have essentially identical, neutral colors," says Weaver.

The new results further strengthen the hypothesis that Pluto and its satellites formed after a collision between two Pluto-sized objects nearly 4.6 billion years ago. "Everything now makes even more sense," says Stern. "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."

The researchers hope to make additional Hubble color observations, in several more filters, to see if the similarity among the satellites persists to longer (redder) wavelengths. They have proposed to obtain compositional information on the new satellites by observing them at near-infrared wavelengths, where various ice and mineral absorptions are located. The researchers also hope to better refine the orbits of P1 and P2 and measure the moons' shapes and rotational periods.

The Hubble observations were made in support of NASA's New Horizons mission to Pluto and the Kuiper Belt. New Horizons launched on Jan. 19, 2006, and will fly through the Pluto system in July 2015, providing the first close-up look at the ninth planet and its moons. Stern leads the mission and science team as principal investigator; Weaver serves as the mission's project scientist. The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., manages the mission for NASA's Science Mission Directorate and operates the New Horizons spacecraft. For more information on the mission, visit http://pluto.jhuapl.edu. . 

Source: International Astronomical Union Circular (No. 8686) 

At 4.3 light years distant, Alpha Centauri is the closest star in the heavens and the most likely detination for mankind's first instellar exploration. Getting there at speeds of even one-tenth the speed of light (well beyond our current capabilities) will require a generation of years... in each direction.

"Interstellar flight is in our future, although we cannot know when," writes Paul Gilster in this informative survey of the propulsion and communications challenges that must be met. "The challenges are immense but achievable, if only by our descendants."

Gilster reviews the surprisingly large body of scientific literature on the subject of interstellar flight and introduces researchers at NASA, the Jet Propulsion Laboratory and elsewhere who are seriously laboring on the issues.

"A single insight from any one of a number of running experiments in different areas could change everything," he writes. "The field is top heavy with ideas, alive with the loopy challenge of pushing a spacecraft to a sizeable percentage of the speed of light."