Complex sentence: On 14 July 2015, Pluto and its five known moons are due to be visited by spacecraft for the first time when the "New Horizons" probe performs a flyby and attempts to take detailed measurements and images.
Split into simpler sentences: On 14 July 2015, Pluto and its five known moons are due to be visited by spacecraft for the first time. The "New Horizons" probe will perform a flyby and attempt to take detailed measurements and images.