As early as the sixteenth century, we have wondered if Earth – and even the other planets in the Solar System – were unique. Our quest to find these extrasolar planets (exoplanets) has been hindered by our technological ability to see them. The first exoplanet wasn’t confirmed until 1992. In just 20 short years, astronomers have observed about 1000 of these worlds around other stars.


Upon the discovery of the first exoplanets, scientists asked a simple yet profound question, “are any of them habitable?” Not only might one such planet provide a sanctuary for humanity, but, it might even host life similar to ours. To date, scientists have discovered five exoplanets that might be habitable for our form of life.

 Meet the Potential Second Earths:

1) Gliese 581 g: Currently, this planet hosts the best possibility for being habitable. It orbits around Gliese 581. This star is a red dwarf star, which means that it is far cooler and smaller than our own Sun. As such, any habitable world would need to orbit much closer to the star, otherwise the planets would be nothing more than frozen wastelands. This planet is located about 20 light-years from Earth (making Gliese 581 our Sun’s 89th closest star). Gliese 581 g has an orbital period of 37 days, orbits at a distance of 0.15 Astronomical Units (which is close enough to receive enough heat and light from the star to sustain liquid water and, thus, life). An added bonus? This planet is 3-4 times more massive than Earth, which might help with our population issues.


2) Gliese 667C c: This planet orbits around the third and smallest star in the triple star system of Gliese 667.  Like Gliese 581, this star is just a small red dwarf. Once again, any planet orbiting the star would need to be exceedingly close to the solar surface in order to be habitable. Located about 22.1 light-years from Earth, Gliese 667C c has an orbital period of a mere 28 days (which immediately tells you that the planet is rather close the the star...a good thing, indeed). In fact, the planet orbits at a distance of 0.123 AU, and is 3.9 times more massive than Earth. Like the previous planet, Gliese 667C c is a bit larger than Earth, which would give us enough space to alleviate some of the tension that is caused by our continually expanding population. Moreover, it's not so big that the gravity would adversely affect our bodies (at least, not as far as we can tell).



3) Kepler-22 b: This planet is found orbiting the Kepler-22 star. But don't bother trying to find it on a clear, starry night. Unfortunately, Kepler- 22 is invisible to the naked eye. This star is a yellow dwarf, so it more like our own Sun than either of the previous stars mentioned. As such, the orbital period of any planet in the habitable zone will be more akin to our own. This planet seems like it might be the prefect 2nd Earth. Unfortunately, the star itself is located 587 light-years away (that makes for a very long travel time). Kepler-22 b has an orbital period of 289 days, orbits at a distance of 0.85 AU. Unfortunately, there are a few things that we still don't know about this world. We know that it is a nice 75F (22C). However, its mass, for example, is still unknown.



4) HD 85512 b: This planet orbits around the orange dwarf star HD 85512 (also known as Gliese 370). This star is about 36 light-years from Earth (you've probably noticed that most of these stars are rather far away. It takes us over a decade just to reach Pluto. So unfortunately, any trip to these stars will take quite a long time...think hundreds of thousands of years). HD 85512 b has an orbital period of 54 days, so two months on Earth would be a year on this's really kind of neat when you thin about it. If you were born here, you would be 24 a little after corresponding Earthlings turned 4.  The planet orbits at a distance of a mere 0.26 AU, which is not very far from the star when you are thinking in cosmic terms. And the planet is roughly 3.6 times more massive than Earth.




5) Gliese 581 d: This is the last planet on our list and orbits the same star (Gliese 581) as the first planet I mentioned. Gliese 581 d has an orbital period of 67 days, orbits at a distance of 0.22 AU, and is 5.6 times more massive than Earth.

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