Over the past few years, evidence has emerged that something unexpected occurs in the evolution of rotation and magnetism near the middle of a star's main-sequence lifetime. For solar-type stars the transition begins near the age of the Sun, when rotation becomes too slow to imprint Coriolis forces on the global convective patterns, reducing the shear induced by differential rotation, and disrupting the large-scale dynamo. From the best data currently available, the Sun may have entered this phase a few hundred million years ago, just as life was emerging from the oceans onto land. Younger stars bombard their planets with radiation and charged particles that are hostile to the development of complex life, but older stars appear to quiet down substantially and provide a more stable environment. I will summarize the evidence for this unexpected transition, outline our current understanding of its likely origin, and speculate on the implications for planetary habitability beyond stellar middle-age.
Travis Metcalfe / Space Science Institute- WDRC
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