Photo credit: NASA
By Peter Kelley
We know the Earth is habitable because—well, here we are. But would it look like a good candidate for life from hundreds of light-years away?
Good, but perhaps not great, according to astronomer Rory Barnes of the University of Washington-based Virtual Planetary Laboratory. It’s a question, among many others, that he and co-authors asked in a recent paper.
Barnes, a research assistant professor of astronomy, colleagues are drawing up a “habitability index for transiting planets” that ranks exoplanets to help prioritize the search for life.
Astronomers spot possible exoplanets, or those beyond the solar system, not through direct observation but by the dimming of light that happens when the worlds pass in front of, or “transit” their host star. Many factors go into judging a world’s possible habitability, including the amount of energy it gets from its star, the distance and radius of its orbital path and the behavior of its neighbor planets. Spectrometry is used to estimate the mass and radius of the host star, from which astronomers can the estimate the size of the planet itself.
They use this data to create a model of a planet—”an idea of a planet,” Barnes said, which is then compared with information about other worlds. “And you basically try and sort out, do I think that could reasonably be a planet that’s habitable?”
But validating, or confirming planets is methodical, time-consuming work, and access to the big telescopes needed is expensive. The habitability index helps astronomers rank and prioritize planets to help determine which are worthy of closer study.
Managing these myriad calculations, the index gives the Earth, if observed from afar as we now observe faraway planets, about an 82 percent chance of being right for life.
But wait—only 82 percent?
Why wouldn’t the Earth—the single example of a life-hosting world in all our experience—score a perfect, 100 percent rating?
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