A US-Israeli astronomy team has discovered a very small heavenly body - less than a kilometer across - in the Kuiper belt at the far reaches of our solar system. The researchers, which included five Israelis from the Hebrew University of Jerusalem, Tel Aviv University and the Weizmann Institute of Science, found it beyond Neptune's orbit, according to an article published in the December 17 issue of the prestigious journal Nature. Until now, only a single object has been found in the Kuiper belt, located around 30 to 60 astronomical units (au) from the Sun (each au is equivalent to 150 million kilometers). The belt contains ice-and-rock bodies that are remnants of the primordial solar system. The researchers, headed by Hilke Schlichting of the California Institute of Technology, suggest that because there are few such bodies in the belt, they apparently "are being lost to collisional erosion." Kuiper belt objects (KBOs) cannot be seen with a telescope, but they can be detected when they pass in front of a distant star, a phenomenon called occultation. The team searched for occultations in four-and-a-half years of data from the Hubble Space Telescope's fine guidance sensors, which control the telescope's movement by observing guide stars. Using methods most likely to detect KBOs with radii of 200 to 500 meters, the authors found only one occultation, by a body with a radius of about 500 m., at about 45 au. The authors said there was only a small number of KBOs in this size range, compared with extrapolations from the numbers of larger objects. They concluded that sub-kilometer-sized objects were undergoing collisional erosion, the same process that creates the debris disks observed around other stars.