Pluto is 4.67 billion miles away from Earth. At a certain condition, the two celestial bodies are only 2.66 billion miles apart. NASA sent the New Horizons spacecraft on a mission to visit Pluto, and it is expected to reach the Pluto-Charon system 11 years after its take-off on Jan. 19, 2006.
The distances between planets in the solar system vary constantly because they travel in elliptical orbits rather than perfect circles. The heavenly bodies are in constant motion, which is why they are not always in preferred positions at the time of a mission launch. This factor causes delay to reach a target destination.
Probes sent by scientists to learn more about celestial bodies need a lot of help during space travel. Satellites frequently require fuel-less acceleration, therefore they use the gravity of planets, moons and even the sun. The New Horizons mission, only the fifth probe to cross interplanetary space, is trying to surpass what the Voyager and Pioneer accomplished. The spacecraft already passed by Mars and received gravity assistance from Jupiter on its way to Pluto. Its closest approach to the dwarf planet is expected to occur at 7:49:59 a.m. EDT on July 14, 2015, based on NASA's calculation.