The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.

The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69’s origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

We describe the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). This instrument consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon to horizon and a nadir-looking photometer system (NPS). The SIS produces simultaneous multispectral images over the spectral range 1 150 to 1800A. The NPS consists of three photometers with filters designed to monitor the airglow at 4278A and 6300A and the terrestrial albedo near 6300A. SSUSI will fly on the DMSP Block 5D3 satellites S-16 thru S-19. The instruments will be calibrated at the Applied Physics Laboratory's Optical Calibration Facility. SCIENTIFIC OBJECTIVESThe Block 5D3 Special Sensors will provide the first comprehensive operational space-based investigation of the physical and chemical processes in the Earth's upper atmosphere (above 80km). The upper atmosphere is the region that contains the mesophere, thermosphere, and ionosphere. This region is poorly understood due to the difficulty in carrying out in situ measurements, its inherent complexity, and the need to develope a comprehensive global picture of this environment. While the basic physics that controls this region is understood, it does represent a difficult region to model since the atmospheric temperature and temperature gradients reach their largest values, composition changes from molecular to predominantly atomic, complex chemical and electrodynamic processes become the major determinants of composition, and where the combination of these effects prevent an adequate global description of the upper atmospheric "weather".The study of the upper aunosphere has witnessed a major change in the last decade as ultraviolet technology has made the transition from spectroscopy to remote sensing. Traditionally the concern of optical aeronomers (scientists who study the structure, composition, and dynamics of the upper atmosphere using optical means) had been the identification of the excitation and emission mechanisms of spectral features. With the advent of an adequate physical description of the phenomena it has become possible to move beyond the simple identification of features to their interpretation in terms of geophysical parameters. APL is building four new state-of-the-art sensors for DMSP. These sensors, the SSUSI, are intended to provide information on the state of the upper atmosphere and the aurora on a global basis. In order for the data to be of use tothe user community, rapid, efficient, and accurate operational algorithms must be developed to convert the radiance observations into environmental parameters. The development of the SSUSI data handling system and the operational uses of SSUSI data are described in another SPIE proceeding paper1 and in greater detail in an APL Technical Report2.The FUV is ideally suited to determining thermospheric and ionospheric environmental parameters. It possesses optical signatures of all the major thermospheric species 0, N2, and O (O is seen in absorption on the limb) and the dominant F-region ion, 0÷ (on the nig...

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