The Kuipers orbit beyond Neptune and may include Pluto and its satellite Charon among its numbers
This discovery is published in the Oct. 26 issue of "Nature." Stephen Tegler, associate professor of physics and astronomy at NAU, and William Romanishin, associate professor of physics and astronomy at Oklahoma, have been using the largest telescope in the world, the Keck 10-m telescope in Hawaii to measure the surface colors of Kuiper belt objects, an ancient reservoir of giant comet-like objects at and beyond the orbits of the most distant planets, Neptune and Pluto.
Tegler and Romanishin find the surface colors of the icy objects to come in only two colors, red and gray, and the objects that stay the farthest from the Sun come only in red.
"Our findings are controversial because they are so unexpected,"Tegler said. "Most astronomers expected the colors of Kuiper belt objects to be the same."
Kuiper belt objects are thought to have all formed at about the same extremely large distance from the Sun, about four billion miles away, and therefore should be made of the same stuff and have the same colors, Tegler said.
Much closer to the Sun, the asteroid belt marks the boundary between rocky, inner planets like Earth, and gaseous, outer planets, like Jupiter.
A change in the surface colors between the rocky asteroids in the inner and outer belt is easier to explain.
Why red and gray surface colors?
In the darkness of the Kuiper belt where temperatures reach a chilly minus 380 F, the surfaces of some objects are rich in a material that strongly absorbs blue sunlight.
Upon reflection, the lack of blue sunlight gives the objects very red colors. The gray objects contain little or none of the material that strongly absorbs blue sunlight. Upon reflection, the material on the surface of these objects does not change the colors in sunlight, and astronomers refer to the material as gray in color.
Two different surface types is a puzzle
Romanishin said, "The existence of two surface colors suggests to us that something important and unexpected happened long ago in the outer solar system."
The objects are named after the Dutch-expatriate and Arizona astronomer, Gerald P. Kuiper. In 1950, Kuiper theorized that the Solar System extended beyond Pluto. In 1992, David Jewitt and Lane Luu, astronomers at the University of Hawaii, discovered the first Kuiper belt object. Today there are nearly 400 known Kuiper belt objects that range in size from small cities to the planet Pluto which is smaller than the Moon.
Tegler said, "We found patterns that we did not know existed four or five years ago. Once we understand the patterns, they will give us additional insight into history of the solar system. What we have now is the ability to ask more questions."