Astronomer Chris Impey examines the possibilities of the universe in his new book Beyond. "I like the idea that the universe — the boundless possibility of 20 billion habitable worlds — has led to things that we can barely imagine," he says. In the 1970s, NASA Ames conducted several space colony studies, commissioning renderings of the giant spacecraft which could house entire cities. Rick Guidice/NASA Ames Research Center hide caption

itoggle caption Rick Guidice/NASA Ames Research Center

This image of a "red spot" on Mercury, which is thought to be the result of a volcanic explosion, was sent to Earth by the Messenger probe in 2011. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington hide caption

itoggle caption NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

A giant cluster of about 3,000 stars called Westerlund 2. The cluster resides in a raucous stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina. NASA, ESA, STScI/AURA hide caption

itoggle caption NASA, ESA, STScI/AURA

A view of a phytoplankton bloom near Alaska's Pribilof Islands. The milky green and light blue shading of the water indicates the presence of vast populations of microscopic phytoplankton. NASA hide caption

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This artist rendering shows Kepler-11, a sun-like star around which six planets orbit. A planet-hunting telescope is finding whole new worlds of possibilities in the search for alien life, including more than 50 potential planets that initially appear to be in habitable zones. The agency's chief scientist said Tuesday there will be "strong indications" of alien life within a decade. NASA/AP hide caption

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NASA astronaut Scott Kelly is seen inside a Soyuz simulator at the Gagarin Cosmonaut Training Center on March 4 in Star City, Russia. Kelly, along with Russian cosmonaut Mikhail Kornienko of the Russian Federal Space Agency, are scheduled for launch Friday aboard a Soyuz TMA-16M spacecraft from the Baikonur Cosmodrome in Kazakhstan. NASA/Bill Ingalls hide caption

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New research suggests that Saturn's tiny moon Enceladus has warm oceans hiding beneath its icy crust. NASA/JPL/Space Science Institute hide caption

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Astronomers have known about Ceres for centuries, but they don't really know what to make of it. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA hide caption

itoggle caption Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

An image of Ceres taken by NASA's Dawn spacecraft shows that the brightest spot on the dwarf planet has a dimmer companion. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA hide caption

itoggle caption NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

An image taken with the NASA/ESA Hubble Space Telescope of the galaxy cluster SDSS J1038+4849 shows that it seems to be smiling. The space agency says it's the result of a symmetrical alignment of the galaxy cluster and the telescope — along with a powerful gravity field that can bend light. NASA & ESA hide caption

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Leland Melvin with his dogs, Jake and Scout. "I snuck them into NASA to get this picture," Melvin says. Courtesy of Leland Melvin hide caption

itoggle caption Courtesy of Leland Melvin