science investigation tool, as well as spectroscopic and other experiments, to characterize the global geology and morphology of Pluto and its moon Charon, map their surface composition and analyze Pluto's neutral atmosphere and its escape rate. New Horizons also photographed the surfaces of Pluto and Charon. Photographs of Pluto taken on 14 July 2015 taken 15 minutes after New Horizon closest approach, from a distance of 18,000 kilometers and sent to Earth on 13 September 2015 show a near-sunset on Pluto with details of the surface and a haze in the atmosphere. Future mission concepts No follow-up missions to New Horizons have been formally planned, but at least two mission concepts have been studied. In April 2017, a workshop met in Houston, Texas to discuss ideas for a follow-up mission. Possible objectives discussed by the group for a follow-up mission include mapping the surface at 30 feet per pixel, observations of Pluto's smaller satellites, observations of how Pluto changes as it rotates on its axis, and topographic mapping of Pluto's regions that are covered in long-term darkness due to its axial tilt. The last objective could be accomplished using infrared laser pulses. According to New Horizons principal investigator Alan Stern, “If we send an orbiter, we can map 100 percent of the planet, even terrains that are in total shadow." Stern and David Grinspoon have also suggested that an orbiter mission could search for evidence of the subsurface ocean hinted at in New Horizons data. Shortly after the New Horizons flyby, Stern suggested a Charon lander as a follow-up that would observe Pluto from Charon's surface. However, such a lander would only observe the Charon-facing hemisphere of Pluto, as Pluto and Charon are tidally locked. Since the Houston workshop, Stern changed his mind to advocate instead for a Cassini-style orbiter that would use Charon's gravity to adjust its orbit while studying Pluto and its moons. The probe could use electric propulsion similar to NASA's Dawn mission. It would then have the option of using Charon's gravity to leave the Pluto system after all Pluto science objectives are completed and study new KBOs beyond Pluto. Stern envisaged the probe being launched in 2030, marking the 100th anniversary of Pluto's discovery, and spending 7–8 years traveling to the Pluto system. Fusion-Enabled Pluto Orbiter and Lander The Fusion-Enabled Pluto Orbiter and Lander was a 2017 phase I report funded by the NASA Innovative