By Barb Williamson
Flagstaff - March 8, 1998 - Astronomers at Northern Arizona University and the University of Oklahoma discovered a mystery at the edge of the solar system -comet-like bodies known as Kuiper Belt Objects have two distinct surfaces.
In the March 5 issue of the science journal Nature, Stephen Tegler, an assistant professor in the NAU Physics and Astronomy department, and William Romanishin, from the University of Oklahoma, report that the objects exhibit neutral-colored surfaces and extraordinarily red surfaces.
"The reason for two distinct surfaces is a mystery. The resolution of the mystery will likely provide scientist with a more complete picture of planet formation and evolution in the outer solar system," Tegler said.
In 1992, astronomers David Jewitt and Jane Luu discovered the first object in an ancient reservoir located beyond Neptune's orbit. Today about 60 Kuiper Belt objects are known to exist and are orbiting the sun. The objects are smaller than planets but larger than comets.
The discovery was revolutionary because it showed our solar system does not end with Pluto. In fact, many astronomers now consider the tiny planet Pluto to be the largest member of the Kuiper Belt.
"The discovery is exciting because many astronomers expected all Kuiper Belt objects to have similar surface colors," Romanishin said.
Tegler said he and Romanishin have been engaged in this research for about three years. They spent 40 nights making observations at Steward Observatory, State of Arizona research facility on Kitt Peak, west of Tucson, using a 2.3 meter (90-inch) diameter telescope.
"The actual observing of the belt was the tip of the iceberg. We spent countless hours doing image processing with extremely sophisticated computers and software which the NAU and Oklahoma physics and astronomy departments obtained for us," Tegler said.
Objects in the Kuiper Belt are too far from the sun to experience evaporation of their icy material. Tegler and Romanishin were able to probe the surfaces of these objects without shrouds of evaporating gas and dust surrounding the icy bodies. The known Kuiper Belt objects have diameters similar to the width of Oklahoma.
Some comets that are visible to the unaided eye in the night sky are escapees from the Kuiper Belt. These objects make their way into the inner solar system where they are warmed by the sun and form visible tails of evaporating gas and dust streaming away from the central icy body. The central icy bodies of these more familiar comets have diameters similar to the length of Manhattan Island, although the tails can stretch millions of miles.
Since Kuiper Belt objects are more than one million times fainter than the faintest stars visible to the unaided eye, the astronomers used a highly sensitive electronic camera called a charge-coupled device (CCD) in combination with the telescope.
Because Kuiper Belt objects are so small and far from the Earth, astronomers cannot take actual pictures of the surfaces of the objects, but they can measure the brightness of sunlight that reflects off the surfaces of the objects.
The red Kuiper Belt comets may be the most intriguing objects for further study since they may have carbon and nitrogen-rich compounds on their surfaces and these compounds may represent the initial building blocks of life in our solar system.
The idea that comet impacts on the primitive Earth delivered prebiotic material important for the evolution of life on Earth has been around for nearly a century. By virtue of their stable, circular orbits and great distances from the sun, the present-day surfaces of Kuiper Belt comets provides us with a window on the very young solar system. In the years to come studies will be able to identify the types of compounds that likely impacted the surface of the Earth, Tegler said.
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