Nearly a Decade of Cosmic Ray Observations in the Very Local Interstellar Medium

Abstract

In 2012, the centennial year of the discovery of cosmic rays, Voyager 1 crossed the heliopause and began making the very first in-situ measurements of the surrounding interstellar medium. Joined by Voyager 2 in 2018, these twin spacecraft continue to provide critical data of cosmic rays in a surprising, previously-unexplored plasma regime. Here, we highlight some of the discoveries and insights that have emerged from nearly a decade of cosmic ray observations in the very local interstellar medium, addressing topics such as: i) the behavior of cosmic rays at the heliopause boundary, ii) the characteristics of the low-energy spectrum (down to a few MeV/nuc), iii) the discovery of a time-varying, species-dependent anisotropy, and iv) their relationship to solar-transients that pass through the heliosphere and transmit pressure waves into the VLISM.