As a star spins-down during the main sequence , its wind properties are affected .
In this work , we investigate how the Earth ’ s magnetosphere has responded to the change in the solar wind .
Earth ’ s magnetosphere is simulated using 3D magnetohydrodynamic models that incorporate the evolving local properties of the solar wind .
The solar wind , on the other hand , is modelled in 1.5D for a range of rotation rates \Omega from 50 to 0.8 times the present-day solar rotation ( \Omega _ { \odot } ) .
Our solar wind model uses empirical values for magnetic field strengths , base temperature and density , which are derived from observations of solar-like stars .
We find that for rotation rates \simeq 10 \Omega _ { \odot } , Earth ’ s magnetosphere was substantially smaller than it is today , exhibiting a strong bow shock .
As the sun spins down , the magnetopause standoff distance varies with \Omega ^ { -0.27 } for higher rotation rates ( early ages , \geq 1.4 \Omega _ { \odot } ) , and with \Omega ^ { -2.04 } for lower rotation rates ( older ages , < 1.4 \Omega _ { \odot } ) .
This break is a result of the empirical properties adopted for the solar wind evolution .
We also see a linear relationship between magnetopause distance and the thickness of the shock on the subsolar line for the majority of the evolution ( \leq 10 \Omega _ { \odot } ) .
It is possible that a young fast rotating Sun would have had rotation rates as high as 30 to 50 \Omega _ { \odot } .
In these speculative scenarios , at 30 \Omega _ { \odot } , a weak shock would have been formed , but for 50 \Omega _ { \odot } , we find that no bow shock could be present around Earth ’ s magnetosphere .
This implies that with the Sun continuing to spin down , a strong shock would have developed around our planet , and remained for most of the duration of the solar main sequence .