Breaking correlation in the inflow parameters of interstellar neutral gas in direct-sampling observations

TL;DR

This paper investigates the correlation between temperature, direction, and speed of interstellar neutral gas inflow observed by IBEX and proposes methods to break this correlation using improved observational capabilities, such as longer orbital arcs and adjustable boresights.

Contribution

The study identifies the causes of parameter correlation in IBEX observations and suggests observational strategies and instrument modifications to independently measure inflow parameters.

Findings

Correlation is due to measurement limitations and short observation arcs.

Longer orbital observations or multiple locations can break the correlation.

Adjustable boresight capability enables independent parameter measurement.

Abstract

We analyze the reasons for the correlation between the temperature, direction, and speed of the interstellar neutral gas inflow into the heliosphere, obtained in analyzes of observations performed by the IBEX-Lo instrument onboard Interstellar Boundary Explorer (IBEX). We point out that this correlation is the combined result of the inability to measure the speed of the atoms that enter the instrument and the restriction of the observations to a short orbital arc around the Sun performed by the instrument during observation. We demonstrate that without the capability to measure the speed, but with the ability to perform observations along longer orbital arcs, or from at least two distant locations on the orbit around the Sun, it is possible to break the parameter correlation. This, however, requires a capability to adjust the boresight of the instrument relative to the spacecraft rotation axis, such as that of the planned IMAP-Lo camera onboard the Interstellar Mapping and Acceleration Probe (IMAP).