Discovering thousands of planets beyond our solar system counts as a “eureka” moment in human exploration. But the biggest payoff is yet to come: capturing evidence of a distant world hospitable to life.
To find another planet like Earth, astronomers are focusing on the 'habitable zone' around stars--where it's not too hot and not too cold for liquid water to exist on the surface.
We begin the search on familiar ground. On this planet, currently our sole example of a life-bearing world, the need for water is non-negotiable. So astronomers search the cosmos for similar environments. Around almost every “normal” star, including our sun, we can draw a band of potential habitability: the right distance and temperature for liquid water to exist. The key, of course, is a planetary surface where the water could pool. Both stars and planets come in many types and sizes, and the interplay of these factors determines the extent and influence of this “habitable zone.”
A giant, hot-burning star’s habitable zone would be found at a much greater distance than that of a smaller, cooler stellar dwarf. And if we stick with the plan—hunting first for what we know—then small, rocky worlds are our best bet for finding evidence of life as we know it (we’ll talk about “life as we don’t know it” in the my other page)
So the ideal candidate is an Earth-sized, rocky world nestled comfortably within its star’s habitable zone—though scientists’ understanding of what makes up a habitable zone continues to evolve.
We begin the search on familiar ground. On this planet, currently our sole example of a life-bearing world, the need for water is non-negotiable. So astronomers search the cosmos for similar environments. Around almost every “normal” star, including our sun, we can draw a band of potential habitability: the right distance and temperature for liquid water to exist. The key, of course, is a planetary surface where the water could pool. Both stars and planets come in many types and sizes, and the interplay of these factors determines the extent and influence of this “habitable zone.”
A giant, hot-burning star’s habitable zone would be found at a much greater distance than that of a smaller, cooler stellar dwarf. And if we stick with the plan—hunting first for what we know—then small, rocky worlds are our best bet for finding evidence of life as we know it (we’ll talk about “life as we don’t know it” in the my other page)
So the ideal candidate is an Earth-sized, rocky world nestled comfortably within its star’s habitable zone—though scientists’ understanding of what makes up a habitable zone continues to evolve.
Wish among the right kind of stars
That’s not the end of the story. While the size and composition of both planets and stars are critical to habitability, so is time. Big bright stars burn out far more quickly than their more modest counterparts. The brightest burn for only a few million years, then flame out; meanwhile, our sun has been shining steadily for 4.5 billion years, with about another 5 billion years to go. At that point it will swell to many times its previous size to possibly engulf Earth and the rest of the inner planets, though any lingering Earth life would long since have burned to a crisp.
cool
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