If the Sun were to evolve into a red giant star, it would have significant consequences for life on Earth and potentially other solar systems as well. Here's what would likely happen:
Earth: As the Sun expands and becomes a red giant, its outer layers would engulf Mercury, Venus, and possibly Earth. The increased radiation and heat from the expanding Sun would render the Earth uninhabitable. The oceans would evaporate, the atmosphere would be stripped away, and the surface would become extremely hot, making it impossible for life as we know it to survive.
Other Solar Systems: The fate of other solar systems would depend on their distance from their own evolving stars. Stars go through different stages of evolution, including red giant phases, and their impact on exoplanets would vary. If an exoplanet is too close to its expanding star, it could experience similar effects as described for Earth. However, planets located farther away might have a chance of surviving, though their climates and conditions would still be dramatically altered.
It's worth noting that the timescale for such stellar evolution processes is measured in millions to billions of years. The Sun is currently in the main sequence phase and is expected to remain so for about another 5 billion years. Therefore, any potential future changes that might affect life on Earth or other solar systems are far beyond the scope of our current understanding.
However, if the long-term habitability of a planet or a solar system is a concern, it is important to consider factors such as the star's age, size, and stability when assessing its potential to support life.