What makes a planet potentially habitable

By Ashley Strickland, CNN

Updated 5:27 PM ET, Mon November 11, 2019

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This artist's impression shows a Neptune-sized planet in the Neptunian Desert. It is extremely rare to find an object of this size and density so close to its star.
Photos: Weird and wonderful planets beyond our solar system
This artist's impression shows a Neptune-sized planet in the Neptunian Desert. It is extremely rare to find an object of this size and density so close to its star.
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This is an artist's impression of the multiplanetary system of newly discovered super-Earths orbiting a nearby red dwarf star called Gliese 887.
Photos: Weird and wonderful planets beyond our solar system
This is an artist's impression of the multiplanetary system of newly discovered super-Earths orbiting a nearby red dwarf star called Gliese 887.
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The newly discovered exoplanet AU Mic b is about the size of Neptune.
Photos: Weird and wonderful planets beyond our solar system
The newly discovered exoplanet AU Mic b is about the size of Neptune.
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This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Proxima b is a little more massive than the Earth.
Photos: Weird and wonderful planets beyond our solar system
This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Proxima b is a little more massive than the Earth.
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This is an artist's illustration of an exoplanet's atmosphere with a white dwarf star visible on the horizon. The starlight of a white dwarf filtered through the atmosphere of an exoplanet that's orbiting it could reveal if the planet has biosignatures.
Photos: Weird and wonderful planets beyond our solar system
This is an artist's illustration of an exoplanet's atmosphere with a white dwarf star visible on the horizon. The starlight of a white dwarf filtered through the atmosphere of an exoplanet that's orbiting it could reveal if the planet has biosignatures.
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This is an artist's illustration of the Kepler-88 planetary system, where one giant exoplanet and two smaller planets orbit the Kepler-88 star. The system is more than 1,200 light-years away.
Photos: Weird and wonderful planets beyond our solar system
This is an artist's illustration of the Kepler-88 planetary system, where one giant exoplanet and two smaller planets orbit the Kepler-88 star. The system is more than 1,200 light-years away.
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This is an illustration of newly discovered exoplanet Kepler-1649c orbiting around its host red dwarf star.
Photos: Weird and wonderful planets beyond our solar system
This is an illustration of newly discovered exoplanet Kepler-1649c orbiting around its host red dwarf star.
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This artist's illustration shows the night-side view of the exoplanet WASP-76b, where iron rains down from the sky.
Photos: Weird and wonderful planets beyond our solar system
This artist's illustration shows the night-side view of the exoplanet WASP-76b, where iron rains down from the sky.
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This is an artist's concept of a ringed planet passing in front of its host star. It shows how "puffy" a ringed planet may look to us from afar.
Photos: Weird and wonderful planets beyond our solar system
This is an artist's concept of a ringed planet passing in front of its host star. It shows how "puffy" a ringed planet may look to us from afar.
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The sizes of the 17 new planet candidates, seen here in orange, are compared to colorized representations of Mars, Earth and Neptune. The green planet is KIC-7340288 b, a rocky planet in the habitable zone of its star.