Worlds Collide,
Forming Pluto

Using 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 the 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.

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 observations were obtained 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 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.

Source: International Astronomical Union Circular (No. 8686)


The Solar System Beyond Neptune
The Solar System Beyond Neptune

edited by M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, and A. Morbidelli

The Kuiper Belt, discovered in 1992, is a region of the Solar System extending beyond the orbit of Neptune to approximately 55 AU from the Sun. Similar to the asteroid belt, yet at least 20 times as wide, it contains a suprising number of objects like dwarf planets (Pluto) and "scattered discs" and "cubewanos."

This text, consisting of papers by over 100 contributing researchers, presents discoveries that have been made in the first 15 yearsof Kuiper Belt exploration. A region of space that was once regio incognita and an impenetrable mystery is now the new frontier of planetary science.

The latest volume in the Space Science Series of the University of Arizona Press, The Solar System Beyond Neptune consists of 35 chapters divided into seven sections that concern population estimates for transneptunian objects, their bulk properties, physical processes, formation and evolution, and a number of indiividually peculiar objects. The final section explores the links and relationships between transneptunian objects and the rest of the solar system.

The result is the most current and authoritative explanation of the solar system's farthest reaches.