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Astronomers have now discovered satellites surrounding seven Kuiper Belt Objects (KBOs) and their large size might betray an unusual formation says Dr Alan Stern, from the Southwest Research Institute, in a paper published yesterday in the Astronomical Journal. KBOs are icy debris leftover from the formation of our Solar System found in the region beyond the planet Neptune. Although the existence of this Kuiper Belt had been postulated for many years the first KBO was not discovered until 1992. Satellites around asteroids have been known since the NASA Galileo flyby of 243 Ida and now many Near Earth Asteroids are known to have one or more natural satellites. The first satellite around a KBO, however, was only discovered last year and yet now seven satellites have been found amongst the 500 known KBOs. It is the large size of these satellites that is becoming difficult to explain.
The satellites of asteroids, such as Dactyl that orbits the main belt asteroid 243 Ida, are generally very small compared with the primary asteroid and may represent debris produced in collisions or even, for NEAs, have been pulled out of the main asteroid by close approaches to planets. The satellites of KBOs, however, are almost the same size as the primary object. These are, therefore, binary objects orbiting each other and their formation is a puzzle.
Both the Earth and Pluto have unusually large Moons compared to the other planets and they are thought to have formed in catastrophic collisions early in their history. Calculations by Stern and colleages, however, suggest there were not enough objects in the Kuiper Belt to form so many large satellites. The origin of satellites around KBO must, therefore, have occurred by some unknown process, says Stern, or they are not as large as we think. Stern suggests that perhaps the KBO satellites are more reflective that the objects they orbit which would make them appear brighter and thus larger to observers. The answer, however, may not be known until better observations can be made either by NASA’s new Space Infrared Telescope Facility (SIRTF), set for launch early next year, or NASA New Horizons mission to Pluto and the Kuiper Belt which is expected to launch in January 2006.
More info: The Astronomical Journal
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