Because they are so distant from the Earth, Centaurs appear as pinpricks of light in even the largest telescopes. Saturn's 200-kilometre moon Phoebe, depicted in this image, seems likely to be a Centaur that was captured by that planet's gravity at some time in the past. Until spacecraft are sent to visit other Centaurs, our best idea of what they look like comes from images like this one, obtained by the Cassini space probe orbiting Saturn. NASA's New Horizons spacecraft, having flown past Pluto six months ago, has been targeted to conduct an approach to a 45-kilometre wide trans-Neptunian object at the end of 2018. Image credit: NASA/JPL-Caltech/Space Science Institute.
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