NEW HORIZONS features are worthy of intensive scrutiny. The highest-resolution images will be near LANDSAT-class in quality, with resolution in the tens of meters. During closest approach, New Horizons’ imagers will map the entire sunlit faces of Pluto and Charon and also map their outer surface compositions. The team hasn’t yet determined exactly how close New Horizons will come to Pluto; pre-launch planning is in the range of 10,000 kilometers (6,200 miles). Once the spacecraft passes Pluto, it will turn around and map the planet’s night side, which will be softly illuminated by the reflected moonlight from Charon. And the spacecraft’s antenna will receive a powerful radio beam from Earth, aimed so that it passes through Pluto’s atmosphere. By measuring the effects of atmospheric refraction on the radio beam as it travels to the spacecraft, and similar effects on ultraviolet sunlight passing through the atmosphere, scientists will be able to plot the temperature and density profile of the atmosphere down to the surface. New Horizons will also sample the density and composition of material escaping from Pluto’s atmosphere, map surface temperatures across Pluto and Charon, study Pluto’s ionosphere, refine the radii and masses of Pluto and its moons, search for dust particles in the Pluto system and search for rings and additional moons – among other studies. After the Pluto-Charon encounter, New Horizons will maneuver to begin a series of what the team hopes could be one to two encounters with other Kuiper Belt Objects over the following five to seven years. Funding that extended mission will require NASA approval. The first exploration of the Pluto-Charon system and the Kuiper Belt will inspire and excite the scientific community and the public. New Horizons will provide invaluable insights into the origin of the outer solar system and the ancient outer solar nebula, the origin and evolution of planet–satellite systems presumably formed by giant impacts, and the comparative geology, geochemistry, tidal evolution, atmospheres and volatile transport mechanics of icy worlds. For more information on what we know about Pluto-Charon, visit the Science section of the New Horizons Web site at http://pluto.jhuapl.edu. New Moons, New Tasks New Horizons Project Scientist Hal Weaver and Principal Investigator Alan Stern led the team that discovered Pluto’s two “new” moons in two sets of Hubble telescope images taken in May 2005. Provisionally designated S/2005 P1 and S/2005 P2, the moons were observed approximately 43,450 kilometers (27,000 miles) away from Pluto – roughly two to three times as far from Pluto as Charon. Their estimated diameters fall between 64 and 200 kilometers, (40 and 125 miles). The Hubble images represented the most sensitive search yet for objects around Pluto – culminating a three-year effort by the New Horizons team to look for additional Pluto satellites using the powerful telescope. Given that detailed view, it’s unlikely that Pluto has any other moons larger than about 10 miles across. While Pluto is the first body in the Kuiper Belt discovered to have more than one satellite, many other bodies in the Kuiper Belt may be multiple-satellite systems. The discovery will lead to new investigations of the Pluto system -- examples of the information these moons will soon yield include improved estimates of the masses and densities of Pluto and Charon, and new constraints on the tidal evolution and origin of the system. When their colors, rotation periods, and sizes are better known, they will shed more light on their own nature. And a better understanding of the Pluto system will (by example) shed light on the nature and context of other KBO satellite systems. Moreover, the discovery means that the New Horizons spacecraft will be even busier than originally planned, since it will have not two, but four bodies to explore. The science and spacecraft teams will develop plans for these observations as they learn more about the moons, and where they’ll be when New Horizons zips through the Pluto system. NASA’s First Mission to Pluto and the Kuiper Belt 13