Nearly 4.3 billion kilometres from Earth, and most of the way to Pluto, NASA's New Horizons spacecraft is in danger of missing out on half of its mission. Project managers face a looming deadline to identify an icy object in the outer Solar System for the probe to fly by after it passes Pluto. A visit to a Kuiper belt object, or KBO, was always meant to be a key part of New Horizons' US$700-million journey, which began in 2006. But there is only a slim chance that astronomers will find a suitable KBO with their current strategy of using ground-based telescopes - and securing time on the orbiting Hubble Space Telescope is far from guaranteed.
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