A Journey Into the Solar System's Outer Reaches, Seeking New Worlds To Explore

NASA's New Horizons spacecraft will visit a tiny and mysterious object in the Kuiper belt on Tuesday, seeking clues to the formation of our cosmic neighborhood. From a report: In June 1983, newspaper headlines declared that NASA's Pioneer 10 spacecraft had left the solar system, crossing beyond the orbit of Neptune. It was the common view of the time: All of the solar system's big, interesting things -- the sun and the nine planets -- were behind Pioneer 10. Thirty-five years later, the Kuiper belt -- the region Pioneer 10 was just entering -- and the spaces beyond are perhaps the most fascinating parts of the solar system. In their vast, icy reaches are clues about how the sun and planets, including ours, coalesced out of gas and dust 4.5 billion years ago. Even farther out might be bodies the size of Mars or Earth, or even a larger one some astronomers call Planet Nine, and technological advances could usher in a new age of planetary discovery.

On Tuesday, New Horizons, the NASA spacecraft that snapped spectacular photographs of Pluto in 2015, will provide humanity with a close-up of one of these mysterious, distant and tiny icy worlds. Its target of exploration is believed to be just 12 to 22 miles wide, known as 2014 MU69 -- its designation in the International Astronomical Union's catalog of worlds -- or Ultima Thule, the nickname bestowed upon it by the New Horizons team. This will be the farthest object ever visited by a spacecraft. New Horizons will speed past Ultima Thule at 31,500 miles per hour and pass within 2,200 miles of the surface. What the probe finds could reveal much about the earliest days of the solar system and what else lies in the Kuiper belt.

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