Stellar composition, structure, and evolution: Impact on habitability

While we can imagine numerous scenarios in which diverse types of planets could support life in exotic conditions, for pragmatic reasons the most attention still goes to an Earth-like situation where a surface or near-subsurface biome is made possible by the presence of liquid water. With few exceptions, by far the most important source of energy determining the planet's surface conditions is instellation from the host star. This is not a constant quantity over the star's life. If long-term stability is necessary to support detectable life, then the stellar evolution must be taken into account when determining habitability. Stellar composition in turn has a fundamental effect on stellar evolution. The range of variation in individual elements observed in nearby stars is much larger than what is considered in most stellar modeling and can result in gigayear-scale changes in the evolution of sun-like stars. Measurements of stellar composition can also provide insight into the nature of the planets themselves.