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Scientists at the Max-Planck-Institute for Radioastronomy in Bonn, Germany, have determined the size of four of the five largest and most distant minor planets in our solar system. Although radiowaves have been used to determine the size and shape of Near Earth Objects during close approaches to the Earth, radar has a limited range and cannot be used to study distant objects. Dr Frank Bertoldi and Dr Wilhelm Altenhoff, however, have used radio observations in quite a different way to determine the size of large Kuiper Belt Objects beyond the orbit of Pluto. They’ve used the IRAM 30-meter telescope in Spain, shown opposite, to measure the thermal radiation of four of the optically brightest minor planets. These objects are heated only slightly by sunlight due to their great distance from the Sun, however, the heat they emit is related directly to their distance and size allowing their diameters to be determined. In contrast the amount of light Kuiper Belt Objects reflects depends on their surface reflectivity and can only give rough estimates of their size.
The Kuiper Belt is a region of icy bodies leftover from the formation of the Solar System and is thought to contain hundreds of millions of objects. Although the Kuiper Belt is far from Earth it is thought to be one source of the comets found within our Solar System some of which can pass close to our planet.
More info: Max-Planck-Institute
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