Applied Physics Laboratory
Johns Hopkins University
Phone: 240-228-7536 or 443-778-7536
For Immediate Release: March 10, 2006
New Hubble Images Show Similar Colors for Pluto's Moons
Finding Supports Theory that Single Collision Created Ninth Planet's
Using new Hubble Space Telescope observations, a research team led by
Dr. Hal Weaver of the Johns Hopkins University Applied Physics
Laboratory and Dr. Alan Stern of Southwest Research Institute has found
that Pluto's three moons are essentially the same color -- boosting the
theory that the Pluto system formed in a single, giant collision.
Publishing their findings in an International Astronomical Union
Circular (No. 8686), 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 images are available on the Hubble Web site at
"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
The other members of the Hubble Space Telescope-Pluto satellite
observing team include Max Mutchler of the Space Telescope Science
Institute, Baltimore; Drs. William Merline, John Spencer, Andrew Steffl,
Elliot Young and Leslie Young of Southwest Research Institute, Boulder,
Colo.; and Dr. Marc Buie of Lowell Observatory, Flagstaff, Ariz.
The Applied Physics Laboratory (APL) is a not for profit laboratory and
division of The Johns Hopkins University. APL conducts research and
development primarily for national security and for nondefense projects
of national and global significance. APL is located midway between
Baltimore and Washington, D.C., in Laurel, Md. For information, visit