NASA space probe 'phones home' in landmark mission to solar system's edge

NASA's New Horizons explorer successfully "phoned home" on Tuesday after a journey to the most distant world ever explored by humankind, a frozen rock at the edge of the solar system that scientists hope will uncover secrets to its creation.

The nuclear-powered space probe has traveled 4 billion miles (6.4 billion km) to come within 2,200 miles (3,540 km) of Ultima Thule, an apparently peanut-shaped, 20-mile-long (32-km-long) space rock in the uncharted heart of the Kuiper Belt. The belt is a ring of icy celestial bodies just outside Neptune's orbit.