The Heliosphere in Time

TL;DR

This paper models how the Sun's heliosphere varies with different interstellar environments, showing that most of the time it resides in low-density regions leading to significantly larger heliospheres.

Contribution

It explores a wide range of interstellar conditions using global models, revealing how heliosphere features depend on interstellar parameters and the Sun's typical environment.

Findings

Heliosphere size is primarily determined by solar wind and interstellar pressure balance.

Most of the Sun's history involves low-density interstellar medium, resulting in larger heliospheres.

Heliosphere boundary locations correlate with interstellar environment parameters.

Abstract

Because of the dynamic nature of the interstellar medium, the Sun should have encountered a variety of different interstellar environments in its lifetime. As the solar wind interacts with the surrounding interstellar medium to form a heliosphere, different heliosphere shapes, sizes, and particle contents result from the different environments. Some of the large possible interstellar parameter space (density, velocity, temperature) is explored here with the help of global heliosphere models, and the features in the resulting heliospheres are compared and discussed. The heliospheric size, expressed as distance of the nose of the heliopause to the Sun, is set by the solar wind - interstellar pressure balance, even for extreme cases. Other heliospheric boundary locations and neutral particle results correlate with the interstellar parameters as well. If the H0 clouds identified in the Millennium Arecibo survey are typical of clouds encountered by the Sun, then the Sun spends ~99.4% of the time in warm low density ISM, where the typical upwind heliosphere radii are up to two orders of magnitude larger than at present.