10 Remarkable Exoplanets


Gliese 876d

The Goldilocks, or habitable, zone is the sweet spot for planets.
The Goldilocks, or habitable, zone is the sweet spot for planets.
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When searching for Earth-like planets, astronomers look for what are known as Goldilocks planets. These planets aren't so far away from their parent star that they're frozen wastelands yet not so near that water boils off the surface. Unfortunately, Gliese 876d isn't a Goldilocks planet. In fact, the planet is nearly 50 times closer to its parent star (Gliese 876) than Earth is to the sun, and it may have a scorching surface temperature of 642 kelvins (almost 700 degrees Fahrenheit or 369 degrees Celsius) [sources: BBC, EPE].

But while Gliese 876d likely won't ever be home to humans, it does hold the distinction of being one of the first rocky super-Earths ever discovered. Thought to have a mass about 7.5 times that of Earth's, Gliese 876d offered in 2005 perhaps the first evidence that planets like our own are out there [source: BBC]. In fact, scientists typically call an exoplanet with a mass that's up to 10 times greater than Earth a super-Earth. Once the mass goes beyond that point, you start to get into gas giant territory.

More encouraging still is the fact that Gliese 876d is only 15 light-years away, proving that Earth-like planets might not only exist, but exist fairly close to home [source: BBC].