New Horizons Solar Wind Around Pluto (SWAP) Observations of the Solar Wind From 11-33 AU

Abstract

The Solar Wind Around Pluto (SWAP) instrument on NASA's New Horizon Pluto mission has collected solar wind observations en route from Earth to Pluto, and these observations continue beyond Pluto. Few missions have explored the solar wind in the outer heliosphere making this dataset a critical addition to the field. We created a forward model of SWAP count rates, which includes a comprehensive instrument response function based on laboratory and flight calibrations. By fitting the count rates with this model, the proton density (n), speed (V), and temperature (T) parameters are determined. Comparisons between SWAP parameters and both propagated 1 AU observations and prior Voyager 2 observations indicate consistency in both the range and mean wind values. These comparisons as well as our additional findings confirm that small and midsized solar wind structures are worn down with increasing distance due to dynamic interaction of parcels of wind with different speed. For instance, the T-V relationship steepens, as the range in V is limited more than the range in T with distance. At times the T-V correlation clearly breaks down beyond 20 AU, which may indicate wind currently expanding and cooling may have an elevated T reflecting prior heating and compression in the inner heliosphere. The power of wind parameters at shorter periodicities decreases with distance as the longer periodicities strengthen. The solar rotation periodicity is present in temperature beyond 20 AU indicating the observed parcel temperature may reflect not only current heating or cooling, but also heating occurring closer to the Sun.

55 pages, 29 Figures, accepted for publication in The Astrophysical Journal Supplements (ApJS)

References in corpus (1)

• The Solar Wind Around Pluto (SWAP) Instrument Aboard New Horizons

Cited by in corpus (8)

• Interstellar Pickup Ion Observations to 38 AU
• In Situ Observations of Preferential Pickup Ion Heating at an Interplanetary Shock
• Misestimation of temperature when applying Maxwellian distributions to space plasmas described by kappa distributions
• The New Horizons Kuiper Belt Extended Mission
• Modeling the Solar Wind at the Ulysses, Voyager, and New Horizons Spacecraft
• The Impact of Turbulent Solar Wind Fluctuations on Solar Orbiter Plasma Proton Measurements
• Deriving the bulk properties of solar wind electrons observed by Solar Orbiter: A preliminary study of electron plasma thermodynamics
• An empirical model of Energetic Neutral Atom imaging of the heliosphere and its implications for future heliospheric missions at great heliocentric distances