A planet more, a planet less?

摘要

The number of objects detected in the Solar System beyond the orbit of Neptune — so-called trans-neptunian objects — is increasing rapidly. This is mainly due to large, sensitive digital detectors on telescopes and sophisti-cated software, running on high-speed com-puters, that can detect moving objects. More than 1,000 of these objects have been discov-ered since the first one — other than Pluto — was detected in 1992. On page 563 of this issue, Bertoldi et al describe observations of the brightest such object, known as 2003 UB_(313). They find that it has a diameter of about 3,100 kilometres, making it the largest Solar System object discovered since Neptune, and the first known trans-neptunian object larger than Pluto.