(Top row, left to right) Titan, Earth's moon, Europa and Enceladus. (Bottom row, left to right) Callisto, Charon, Ariel and lo. NASA hide caption

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Hot On The Trail Of Alien Moons
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In this composite image, the sun has reached its northernmost point in Earth's sky, marking a season change and the first solstice of the year 2004. NASA/ESA hide caption

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Do You Really Know Why Earth Has A Solstice?
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An artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of a star that is similar to our sun. NASA Ames/JPL-Caltech/T. Pyle hide caption

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Artist's concept compares Earth (left) to the new planet, called Kepler-452b, which is about 60 percent larger in diameter. NASA/JPL-Caltech/T. Pyle hide caption

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Kepler Telescope Introduces Earth To A Very Distant Cousin
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A portrait of Pluto (right) and its moon Charon in a colorized, composite image made July 11 during the final approach of the New Horizons spacecraft. Astronomers are eager to get a much closer view of the icy world Tuesday. NASA-JHUAPL-SWRI hide caption

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Planet Or Not, Icy Pluto To Finally Get Its Day In The Sun
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An artist's rendition of the HD 7924 planetary system — just 54 light-years away from Earth — shows newly discovered exoplanets c and d, which join Planet b. Karen Termaura, BJ Fulton/UH IfA hide caption

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Welcome To The Neighborhood: 2 Super-Earths Discovered
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Saturn has a rocky surface, but it's deep beneath the clouds. That makes it hard to tell exactly how long the day is. NASA hide caption

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A Day's A Day The World Around — But Shorter On Saturn
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Planet: bottom of a glass containing half and half, water, food coloring. Moons: bottom of a glass containing coconut milk, water, food coloring. Stars: salt, cinnamon, baking powder, Tums. Navid Baraty hide caption

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Stars over the Cerro Tololo Inter-American Observatory in Chile. Sheppard and Trujillo used the new Dark Energy Camera (DECam) on a telescope there to find the distant dwarf planet 2012 VP 113. Reidar Hahn/Fermilab hide caption

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Hunting For Big Planets Far Beyond Pluto May Soon Be Easier
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This diagram for the outer solar system shows the orbits of Sedna (in orange) and 2012 VP113 (in red). The sun and terrestrial planets are at the center, surrounded by the orbits (in purple) of the four giant planets — Jupiter, Saturn, Uranus and Neptune. The Kuiper belt, which includes Pluto, is shown by the dotted light blue region. Scott S. Sheppard/Carnegie Institution for Science hide caption

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New Dwarf Planet Found At The Solar System's Outer Limits
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Kepler-22b, seen in this artist's rendering, is a planet a bit larger than Earth that orbits in the habitable zone of its star. Some researchers think there might be "superhabitable" worlds that may not resemble Earth. NASA/Ames/JPL-Caltech hide caption

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In Search For Habitable Planets, Why Stop At 'Earth-Like'?
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