Gliese 581g and the Goldilocks Zone

Gliese 581 is a red dwarf star just 20 light-years away from Earth, and so far we’ve found six planets in stable circular orbits around it—including Gliese 581g, a planet three times the mass of Earth that is near the top of the list of potentially habitable exoplanets. For liquid water to exist on the surface of a planet, it can’t be too close or too far from its sun, so there’s a so-called “Goldilocks Zone” where conditions are just right—and Gliese 581g sits right in the middle of it. Other factors such as the planet’s atmosphere influence habitability too, but for now we can’t even know if this one has an atmosphere. Gliese 581g was first detected in 2010 using the Doppler method, which detects planets by noting the shifts in the wavelengths of a star’s light, caused by the “tug” of a planet as it orbits the star. These shifts give astronomers vital information, such as the planet’s mass, its distance from the star, and the shape of its orbit. Though 20 light-years is 200 trillion kilometres away, and that’s a bit of a hike, the Gliese system still might be one of our best options when considering an interstellar mission. Even its existence suggests something amazing: that in a galaxy of over 100 billion stars, planets in the Goldilocks Zone aren’t unique—they actually might be statistically likely.

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(Image Credit: 1, 2)