It's no "former ninth planet," but for New Horizons, 2014 MU69 will have to do as its next destination. After a Hubble survey narrowed down three potential Kuiper Belt targets for the craft, the New Horizons team has arrived at an answer: 2014 MU69, an object just 30 miles around. 

The tiny Kuiper Belt Object is a bit of icy debris from the formation of the solar system. Just as Pluto is teaching the New Horizons teams about the largish-objects that serve as the bricks planets were made of, so too can 2014 MU69 teach the team about the formation of the planets, asteroids, moons, and comets as we know them today. If Pluto-like objects built the planets, NASA says 2014 MU69 would be an example of the sorts of objects that formed Pluto.

The Kuiper Belt marks the beginning of the "third zone" of the solar system, a region of icy asteroids, comets, and dwarf planets that mark some of the most ancient objects in the solar system. After its July flyby of Pluto, New Horizons has just enough fuel to reach one more destination. With a candidate chosen, the team will draft up a proposal for the extended mission, which will then be submitted to Congress. If approved, the team will brace for a flyby in January 2019, though they'll need to fire their engines later this fall to get there. 

New Horizons is still transmitting information back from its flyby of Pluto, a process that will take years at a speed of 1-4 kilobytes per second. But already, the probe is shedding light on an ancient, complex world filled with icy volatiles, geologic activity, and even possibly liquid bodies. Come 2019, New Horizons could provide even better insight into the Kuiper Belt, and whet the appetite for future icy body explorations. 

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John Wenz
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John Wenz is a Popular Mechanics writer and space obsessive based in Philadelphia. He tweets @johnwenz.