Science Opportunities from Observations of the Interstellar Neutral Gas with Adjustable Boresight Direction

TL;DR

This paper explores the potential scientific benefits of using an adjustable boresight detector to observe interstellar neutral gas, enabling comprehensive, seasonally optimized measurements and separation of different ISN populations.

Contribution

It introduces a flexible observation scheme for ISN gas detection that enhances coverage, population separation, and the study of indirect trajectories compared to fixed-direction methods.

Findings

Adjustable boresight enables observation of ISN in the upwind hemisphere.

Full separation of primary and secondary ISN populations is achievable.

Detection of atoms on indirect trajectories provides new insights into ionization rates.

Abstract

The interstellar neutral (ISN) gas enters the heliosphere and is detected at a few au from the Sun, as demonstrated by Ulysses and the nterstellar Boundary Explorer (IBEX) missions. Ulysses observed ISN gas from different vantage points in a polar orbit from 1994 to 2007, while IBEX has been observing in an Earth orbit in a fixed direction relative to the Sun from 2009. McComas et al. 2018 reported about an IMAP-Lo detector on board the Interstellar Mapping and Acceleration Probe (IMAP), with an ability to track the ISN flux in the sky. We present observation geometries for ISN gas for a detector with the capability to adjust the boresight direction along the Earth orbit over a year within a multichoice ISN observation scheme. We study science opportunities from the observations as a function of time during a year and the phase of solar activity. We identify observation geometries and determine the observation seasons separately for various ISN species and populations. We find that using an adjustable viewing direction allows for ISN gas observations in the upwind hemisphere, where the signal is not distorted by gravitational focusing, in addition to the viewing of ISN species throughout the entire year. Moreover, we demonstrate that with appropriately adjusted observation geometries, primary and secondary populations can be fully separated. Additionally, we show that atoms of ISN gas on indirect trajectories are accessible for detection, and we present their impact on the study of the ionization rates for ISN species.