Originally, NASA had considered sending the Voyage 1 spacecraft on a flyby of Pluto in the late eighties. However, the mission was deemed too high a risk and Saturn's moon Titan was deemed a more realistic and interesting target. Therefore, the decision was made to not exercise the Pluto option.

This only served to motivate Dr Alan Stern and a handful of other young planetary scientists in 1989 to successfully appeal to NASA to begin studying the possibility of a mission to Pluto, what would be known as the "Pluto-350". The mission proposal began, however, amid budget cuts at NASA and the mission was deemed too costly.

NASA considered smaller missions with fewer instruments, non-nuclear missions with extended travel times for replacement. Then, in 2001, intense scientific and public pressure eventually convinced NASA to accept mission proposals for Pluto and Kuiper belt flyby missions, known as the "Pluto-Kuiper Belt Announcement of Opportunity".

Five proposals in total were handed to NASA in April 2001, one of which was the New Horizons proposal headed by Dr Stern through the Applied Physics Laboratory. In June 2001 it was selected, along with the competing Jet Propulsion Laboratory's Pluto and Outer Solar System Explorer concept, for US$450,000 of further study.

NASA finally informed Dr Stern that New Horizons had been selected as the mission that would go to Pluto on 29 November 2001. As the Applied Physics Laboratory and the Southwest Research Institute, both of which would develop and lead the mission, were not experienced in planetary missions, it was necessary to reduce the amount of risk in the spacecraft. So cost and schedule became of paramount importance. In total 2,500 individuals worked on the New Horizons mission throughout its development. At the third countdown attempt, on 19 January 2006, the spacecraft took flight aboard an Atlas V rocket, nine years after Pluto's discoverer Clyde Tombaugh had passed away.

New Horizons is a relatively small spacecraft weighing 481 kilograms. Its most striking feature is the 2.1-metre dish antenna for radio contact with the Earth. Beneath the dish is a triangular body containing seven scientific instruments. The instruments weigh less than 30 kilograms and use only 30 watts of energy. There are no solar panels, as at distances of billions of kilometres from the Sun, solar energy is not an option. The energy is derived from a thermoelectric generator which utilizes the radioactive decay of plutonium-238.

Pluto, is thought to have a nitrogen atmosphere and complex seasons. On its surface, it seems to have distinct surface markings, and it may have ice as well. New Horizons flew through Pluto's atmosphere, measured the interaction of the atmosphere with the solar wind, and took detailed pictures of the surface of Pluto and its moons. The probe also analysed Pluto's ultra-thin atmosphere.

The International Astronomical Union (IAU) voted to reclassify Pluto as a dwarf planet in 2006, and declared that Pluto was not a planet because it did not clear the neighbourhood around its orbit.

Pluto was once seen as a misfit in the solar system, but astronomers have found more objects like it in recent years. As at mid-2015, the IAU has designated four other worlds as dwarf planets: Eris, Makemake and Haumea, which are beyond Pluto's orbit, plus Ceres in the asteroid belt.