NASA has discovered the first Earth-size planets outside of our solar system. The discovery was made as part of NASA's Kepler mission and involves the discovery of two planets currently named after the project: Kepler-20e and Kepler-20f.

If the Kepler name sounds familiar, that's because NASA also recently announced the discovery of Kepler-22b, the most Earth-like planet discovered to date. Kepler 22b is orbiting a star similar to our sun, and is capable of possessing liquid water, an essential feature for life to exist on a planet.

Unlike Kepler 22b, Kepler-20e and Kepler-20f are too close to their star to have water, and are thought to be uninhabitable.

According to NASA, Kepler-20e orbits its star/sun every 6.1 days and Kepler-20f every 19.6 days. These short orbital periods mean the surface of the planets are exceptionally hot. Kepler-20f, at 800 degrees Fahrenheit (427ºC), is comparable to Mercury in our solar system. The surface temperature of Kepler-20e, at more than 1,400 degrees Fahrenheit (760ºC), is hot enough that it could melt glass - not exactly a place you'd want to spend a weekend.

Kepler-20e and Kepler-20f are the fourth and fifth planets discovered as part of the Kepler solar system. Both are thought to be rocky, with Kepler-20e about the size of Venus (.87x Earth's size), with Kepler-20f measuring in slightly larger than Earth (1.03x Earth's size).

"The primary goal of the Kepler mission is to find Earth-sized planets in the habitable zone," said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of a new study published in the journal Nature. "This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them."

What do you think? Are there other Earth-like planets out there?

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