Authors: Heather Elliott, John Richardson, George Livadiotis, Tae Kim, Dave McComas, Eric Zirnstein, Pawel Swaczyna, Alan Stern, Randy Gladstone, Pontus Brandt, Fran Bagenal, Matt Hill, Ralph McNutt, Leslie Young, Cathy Olkin, Kelsi Singer, Hal Weaver, and John Spencer

We examine the radial evolution of solar wind from the inner to outer heliosphere. We do a direct comparison of radial profiles of solar wind parameters from New Horizons and Voyager 2 observations and discuss the differences in the solar cycle for each data set. For both missions, we find the average radial temperature and density profiles show quite similar radial trends with the density decreasing at nearly a spherical expansion rate (r^-2) and the temperature profile is well above what would be expected for adiabatic expansion. There is no strong radial trend for the solar wind speed, but the variability of the solar wind decreases with increasing distance owing to the wearing down and merging of solar wind structures. In the outer heliosphere the solar wind speed slowly decreases owing to the pickup of interstellar material. This slow decrease in speed is only readily apparent when speeds in the outer heliosphere are compared with concurrent inner heliospheric speed measurements. Beyond about 43 au, the recent New Horizons solar wind speed measurements indicate the solar wind speed is very steady and slow. The Solar Wind Around Pluto (SWAP) instrument on New Horizons also measures the interstellar pickup hydrogen ions. We compare the radial profiles of the interstellar pickup ion density, temperature and thermal pressure to those for the solar wind. These profiles reveal that the thermal pressure of the interstellar pickup ions is significant in the outer heliosphere. The relationship between the solar wind temperature and density evolves significantly with increasing distance. Previously when we characterized the temperature-density relationship with a power law fit characterized by a polytropic index for the solar wind we found the polytropic index decreased significantly with increasing distance. Extending this analysis using the more distant New Horizons observations we find the solar wind polytropic index has leveled off and is not decreasing as rapidly.