The exoplanetary magnetosphere extension in Sun-like stars based on the solar wind -- solar UV relation

TL;DR

This study investigates the relationship between solar activity, solar wind properties, and Earth's magnetosphere, extending the findings to Sun-like stars using chromospheric proxies and stellar data over multiple solar cycles.

Contribution

It establishes a link between solar UV emission and solar wind parameters, enabling the estimation of exoplanetary magnetosphere sizes around Sun-like stars based on stellar activity proxies.

Findings

A 3.2-year lag between Ca II K index and solar wind speed.

Correlation between solar wind pressure and UV emission.

Model application to Sun-like stars suggests magnetosphere sizes comparable to Earth's.

Abstract

The Earth's magnetosphere extension is controlled by the solar activity level via solar wind properties. Understanding such a relation in the Solar System is important for predicting also the condition of exoplanetary magnetospheres near Sun-like stars. We use measurements of a chromospheric proxy, the Ca II K index, and solar wind OMNI parameters to connect the solar activity variations, on the decennial time scales, to the solar wind properties. The data span over the time interval 1965-2021, which almost entirely covers the last 5 solar cycles. Using both cross-correlation and mutual information analysis, a 3.2-year lag of the solar wind speed with respect to the Ca II K index is found. Analogously, a 3.6-year lag is found once considering the dynamic pressure. A correlation between the solar wind dynamic pressure and the solar UV emission is found and used to derive the Earth's magnetopause standoff distance. Moreover, the advantage of using a chromospheric proxy, such as the Ca II K index, opens the possibility to extend the relation found for the Sun to Sun-like stars, by linking stellar variability to stellar wind properties. The model is applied to a sample of Sun-like stars as a case study, where we assume the presence of an Earth-like exoplanet at 1 AU. Finally, we compare our results with previous estimates of the magnetosphere extension for the same set of Sun-like stars.