Weekly Science Update

Wednesday, October 17, 2007
Detecting Objects in the Outer Solar System
Beyond the orbit of Neptune lies a vast expanse of space sprinkled with smaller, icy bodies; this region is known as the Kuiper Belt. Named after the Dutch-born American astronomer Gerard P. Kuiper, the Kuiper Belt extends beyond Neptune to approximately four times Neptune's distance from the Sun. Pluto, during most of its orbit, lies in the Kuiper Belt, but Pluto is neither the only Kuiper Belt Object (KBO), nor the largest KBO. Hundreds of thousands of bodies a few kilometers or less in size are thought to populate the Kuiper Belt, along with fewer, larger objects.

Astronomers first began thinking about the Kuiper Belt when trying to explain the origins of comets. Today they realize that most comets originate from an even more remote part of the solar system, the Oort Cloud, but that some comets and many other icy bodies lie in the closer-in Kuiper Belt. Both realms contain leftover material from the primordial days when the planets were forming. So far over 300 KBOs have been discovered. Their story is central to the story of the birth of the solar system and its planets, and astronomers (who have begun spotting evidence of similar Belts and Clouds around other stars) are working hard to find out as much as they can about these small bodies. But KBOs are small, cold, and far away. They are not very easy to find or to study.

SAO astronomers Matt Lehner and Charles Alcock, together with students Taryn Nihei and Federica Bianco and two colleagues, have proposed a novel technique to detect KBOs and objects in the Oort Cloud: searching for occultations. A stellar occultation is the dimming of the light of a background star by a foreground object that happens to pass across our line of sight to the star. The scientists have calculated how a transit by a KBO would look, carefully taking into account a range of possible KBO diameters, diffraction effects, and other phenomena. There are several new telescopes being considered for development as tools to study KBOs, and the team also evaluates their chances of success using their new calculations. They conclude that ground-based telescopes with the appropriate instruments, including the MMT on Mt. Hopkins, could successfully detect hundreds of KBOs and Oort Cloud objects; a space-based facility could detect over 140,000. In order to be seen as practical and generate community support, all such surveys require quantitative estimates like the ones that this new study provides. This paper ultimately advances the cause of such surveys, and with them our ability to learn more about the primordial members of our solar system family.

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