The Structure of the Global Heliosphere as Seen by In-Situ Ions from the Voyagers and Remotely Sensed ENAs from Cassini

Abstract

The exploration of interplanetary space and our solar bubble, the heliosphere, has made a big leap over the past two decades, due to the path-breaking observations of the two Voyager spacecraft, launched more than 44 years ago. Their in-situ particle and fields measurements were complemented by remote observations of 5.2 to 55 keV Energetic Neutral Atoms (ENA) from the Cassini mission (Ion and Neutral Camera-INCA), revealing a number of previously unanticipated heliospheric structures such as the “Belt”, a region of enhanced particle pressure inside the heliosheath. The Suprathermal Time Of Flight (HSTOF) instrument on the Solar and Heliospheric Observatory (SOHO) also provided information of 58–88 keV ENAs from the heliosphere. In this chapter we provide a brief discussion for the contribution of the Voyager 1 and 2 Low Energy Charged Particle (LECP) observations that provided “ground truth” to the ENA images from Cassini/INCA towards addressing fundamental questions for the heliosphere’s interaction with the Very Local Interstellar Medium.

The Early History of Heliospheric Science and the Spacecraft That Made It Possible

“… 2019 ) (see also Dialynas et al. 2022 , this journal). Voyagers 1 & 2 are now exploring the very local interstellar medium in situ , continuing to make surprising, remarkable, and profound discoveries and measurements that will fuel our understanding of the interaction of the solar wind for the next decade despite having only enough electrical power and thruster fuel to keep its current suite of science instruments on until 2025 or a little later.…”

The Structure of the Large-Scale Heliosphere as Seen by Current Models

“…( 2021a ) and discussed by Dialynas et al. ( 2022 ), ENA maps at IBEX-Hi cannot distinguish between the two solutions. We expect that higher-energy ( ) ENA maps will differ between these models, since PUIs survive at these energies for longer distances before being depleted due to charge exchange, so ENA data at these higher energy channels could help determine the structure of the heliotail.…”

“…2022 ; Dialynas et al. 2022 ; Giacalone et al. 2022 ), as well as Gkioulidou et al (2022, in press).…”

“…The combined use of Cassini /INCA ENAs and V1/V2 Low Energy Charged Particle (LECP) measurements (Dialynas et al. 2022 ) gave the opportunity to accurately estimate the HS thickness in both directions (Krimigis et al. 2011 ; Dialynas et al.…”

“…2022 ; Dialynas et al. 2022 ), which were only recently complemented by the New Horizons probe. The scientific exploration of the outer heliosphere has been, and continues to be, a highly successful joint effort of observational campaigns (both in situ and remote, as with, e.g.…”