ABSTRACT

Voyager 1 (V1) traveled into a region of space dominated by interstellar particles and a high magnetic field strength in August 2012. Whether V1 crossed a traditional heliopause or some other sort of “heliocliff,” is not universally agreed upon, but the dramatic disappearance of heliospheric particles that accompanied the other changes leaves no doubt as to the importance of this boundary. While both spacecraft were within the heliosheath, from 2007 to 2012, Voyager 2 (V2) passed back and forth across the boundary between the unipolar and sectored heliosheath. When V2 was inside the sector zone, ions and electrons spanning four orders of magnitude in gyroradius all coherently increased intensity by roughly an order of magnitude compared to the intensities outside the sector region. Voyager 1, during this period, remained almost continually within the sectored heliosheath, with high, steady intensities to match. We present observations from the Low Energy Charged Particle experiment at these two boundaries and highlight their relationship to the heliosphere as a whole.

About the speaker:

Matthew Hill studies energetic particle processes in heliospheric and magnetospheric plasmas, through analysis and operations of space-borne instrumentation, by making in situ measurements, through numerical modeling, through instrumental development, and management of experimental investigations. He is the Deputy Lead of the EPI-Lo (Energetic Particle Instrument – Low Energy) instrument being built at APL as part of the Southwest Research Institute-lead ISIS (Integrated Science Investigation of the Sun) investigation on NASA’s Solar Probe Plus mission, scheduled for launch in 2018. Responsibilities include programmatic activities as well as technical analysis of science issues related to instrument development and significant impact on the EPI-Lo instrument design and configuration itself. He is also a Co-Investigator on NASA’s New Horizons mission and Instrument Scientist for the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument on the New Horizons spacecraft, en route to Pluto. For New Horizons and PEPSSI, he is responsible for planning and conducting the scientific and engineering operations of the energetic particle detector, managing its ground based data-pipeline, coordinating with the instrument PI and supervising the instrument team, analyzing the returned data for instrument health and performance, and conducting scientific studies that utilize the PEPSSI measurements. He has been a member of the Voyager science team since 1998, and the Cassini / MIMI team since 2004, actively contributing to the science, instrumental activities, and the programmatic responsibilities of these projects.

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