The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) on the New Horizons Mission

TL;DR

PEPSSI on New Horizons measures energetic particles around Pluto to analyze its atmosphere, ionosphere, and space environment, providing insights into atmospheric escape and interactions with the solar wind.

Contribution

This paper introduces the PEPSSI instrument, detailing its design, development, and capabilities for measuring energetic particles around Pluto during the New Horizons mission.

Findings

Characterized Pluto's neutral atmosphere and escape rate.

Measured energetic particle environment of Pluto and Charon.

Assessed solar wind interaction with Pluto's system.

Abstract

The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware and accompanying science investigation on the New Horizons spacecraft to measure pick-up ions from Pluto's outgassing atmosphere. To the extent that Pluto retains its characteristics similar to those of a "heavy comet" as detected in stellar occultations since the early 1980s, these measurements will characterize the neutral atmosphere of Pluto while providing a consistency check on the atmospheric escape rate at the encounter epoch with that deduced from the atmospheric structure at lower altitudes by the ALICE, REX, and SWAP experiments on New Horizons. In addition, PEPSSI will characterize any extended ionosphere and solar wind interaction while also characterizing the energetic particle environment of Pluto, Charon, and their associated system. First proposed for development for the Pluto Express mission in September 1993, what became the PEPSSI instrument went through a number of development stages to meet the requirements of such an instrument for a mission to Pluto while minimizing the required spacecraft resources. The PEPSSI instrument provides for measurements of ions (with compositional information) and electrons from 10s of keV to ~1 MeV in a 120 deg x 12 deg fan-shaped beam in six sectors for 1.5 kg and ~2.5 W.