The Solar Wind Environment in Time

TL;DR

This study models the evolution of the solar wind environment over billions of years using magnetogram data from solar analogues, confirming the Skumanich spin-down law and estimating historical wind pressures impacting planetary magnetospheres.

Contribution

It introduces a magnetohydrodynamical wind model driven solely by observed radial magnetic fields to trace the solar wind's evolution and its effects on planetary environments.

Findings

Angular momentum loss rate follows a power law consistent with the Skumanich law.

Solar wind ram pressure decreases by a factor of about 50 over the solar system's lifetime.

Estimated magnetospheric standoff distances vary with stellar age and wind conditions.

Abstract

We use magnetograms of 8 solar analogues of ages 30~Myr to 3.6~Gyr obtained from Zeeman Doppler Imaging (ZDI) and taken from the literature, together with two solar magnetograms, to drive magnetohydrodynamical (MHD) wind simulations and construct an evolutionary scenario of the solar wind environment and its angular momentum loss rate. With observed magnetograms of the radial field strength as the only variant in the wind model, we find that power law model fitted to the derived angular momentum loss rate against time, $t$, results in a spin down relation $\Omega\propto t^{-0.51}$, for angular speed $\Omega$, which is remarkably consistent with the well-established Skumanich law $\Omega\propto t^{-0.5}$. We use the model wind conditions to estimate the magnetospheric standoff distances for an Earth-like test planet situated at 1~AU for each of the stellar cases, and to obtain trends of minimum and maximum wind ram pressure and average ram pressure in the solar system through time. The wind ram pressure declines with time as $\overline{P_{ram}}\propto t^{2/3}$, amounting to a factor of 50 or so over the present lifetime of the solar system.