Ever since Pluto got voted off the island, most astronomers have defined a planet as a body orbiting a star—dead or alive—that is a) massive enough to be rounded by its own gravity, b) not massive enough to ignite itself into starhood, and c) domineering enough to have swept its neighborhood clean of smaller planetary seedlings.
Phew, what a mouthful!
But as we know from our own solar system, not all planets are created equal, and things get really interesting when we try to define the types of planets that might support life.
Traditionally when we think of a habitable world, we think of Earth. Makes sense: To date it's our only frame of reference for a planet that supports plants, animals, even microbes. So it's as good a model as any in terms of what we'd want habitable exoplanets to look like.
A 3-D view of Mount Kilimanjaro in Tanzania, compiled from satellite data
—Image courtesy NASA/JPL/NIMA
Hence the huge emphasis among planet hunters on the so-called Goldilocks Zone, where it's not too hot and not too cold. A planet inside this zone would be just right for liquid water and life-giving sunshine.
In recent years that hypothetical zone has been getting bigger, it seems, especially as expeditions to the deep ocean and volcanic peaks have expanded the conditions in which we thought life could exist.
Enter Rory Barnes, a University of Washington postdoctoral researcher who's here to rain on that parade.
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