Solar Wind at 33 AU: Setting Bounds on the Pluto Interaction for New Horizons

TL;DR

This paper analyzes Voyager 2 data and models to estimate solar wind conditions at 33 AU, providing bounds on the interaction with Pluto's atmosphere for the New Horizons mission.

Contribution

It offers the first statistical analysis of solar wind conditions at 33 AU and estimates the interaction scale with Pluto based on Voyager 2 data and solar activity adjustments.

Findings

Solar wind stand-off distance ranges from 7 to 1000 Pluto radii.

Best estimate of stand-off distance is around 40 Pluto radii.

Solar wind conditions at 33 AU vary significantly, affecting Pluto's atmospheric interaction.

Abstract

The NASA New Horizons spacecraft flies past Pluto on July 14, 2015, carrying two instruments that detect charged particles. Pluto has a tenuous, extended atmosphere that is escaping the weak gravity of the planet. The interaction of the solar wind with the escaping atmosphere of Pluto depends on solar wind conditions as well as the vertical structure of the atmosphere. We have analyzed Voyager 2 particles and fields measurements between 25 and 39 AU and present their statistical variations. We have adjusted these predictions to allow for the declining activity of the Sun and solar wind output. We summarize the range of SW conditions that can be expected at 33 AU and survey the range of scales of interaction that New Horizons might experience. Model estimates for the solar wind stand-off distance vary from approximately 7 to 1000 RP with our best estimate being around 40 RP (where we take the radius of Pluto to be RP=1184 km).