Stars like the Sun evolve from young, fast-rotating and very active stars to older, slowly rotating main-sequence stars like our own Sun. The changes in stellar magnetic fields and stellar activity of such solar analogs with stellar evolution and the change in their rotation period are described in Ch. 2 of Vol. III. In this chapter, we review how the changes in stellar activity of Sun-like stars over stellar evolution translate to changes in their stellar winds, the structure of their interplanetary space and of their astrospheres, the transport of particles, and the propagation and evolution of coronal mass ejections (CMEs). We also review the consequences of CMEs in stellar systems other than our own and their role in planet habitability.

Since the dawn of the space exploration era, great knowledge has been acquired about the solar system's interplanetary space and the heliosphere. The growing amount of spacecraft in-situ measurements of the interplanetary medium (direct measurements of solar-wind particles; see reviews by McComas et al., 2007, and Owens and Forsyth, 2013), as well as increasing amount of global remote-sensing observations monitoring the Sun's photospheric magnetic field, EUV and X-ray coronal radiation, radio emissions, and energetic particles (reviewed by, e.g., Lang, 2009) have revealed a clear dependence of the state of the heliosphere and the interplanetary space on the solar activity level and on the solar magnetic-field structure. These long-term observations also revealed how the frequency of solar eruptions change over the solar cycle (see the review by Webb and Howard, 2012).

Astrospheres in time

Astrospheric structure and evolution with time

The extent and structure of astrospheres are determined by the radially expanding super-Alfvénic stellar wind that drags the stellar magnetic field from the stellar corona through the interplanetary medium, until the wind is stopped by the interstellar medium (ISM; see Ch. 3). It is also determined by the rotation of the star. As a result, each astrospheric magnetic field (AMF) line has one end (or “footpoint”) attached to the stellar surface, while its location at each point in the astrosphere, r(r, θ, ϕ) (for co-latitude θ), is given by the following formula.