A view from Earth of a slender crescent moon in close proximity to the two brightest planets in the sky, Venus and Jupiter. Justin Lane/epa/Corbis hide caption

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A NASA team has attached nearly all of the hexagonal segments that will together make the primary mirror for the James Webb Space Telescope (pictured are practice segments). Chris Gunn/NASA hide caption

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The imagined view from Planet Nine back toward the sun. Astronomers think the huge, distant planet is likely gaseous, similar to Uranus and Neptune. Caltech/R. Hurt (IPAC) hide caption

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An artist's impression of the superluminous supernova as it would appear from a planet in the same galaxy, about 10,000 light-years away. The exploding star is 570 billion times brighter than our sun. Jin Ma/Beijing Planetarium/Science hide caption

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The inset image shows X-ray arcs that astronomers say are signs of galactic burping in the Messier 51 galaxy system, captured by NASA's Chandra X-ray Observatory. X ray: NASA/CXC/Univ of Texas/E.Schlegel et al; Optical: NASA/STScI hide caption

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This platinum-engraved sapphire disk, part of a set illustrating Earth's biodiversity, will be housed in the Earth Chamber of the MoonArk. It's designed by Mark Baskinger with Matt Zywica, Maggie Banks, Christie Chong, Bettina Chou, Adella Guo, Natalie Harmon, Deborah Lee, Deniz Sokullu and Carolyn Zhou. Courtesy of The Moon Arts Project hide caption

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Astrophysicist Richard Gaitskell, from Brown University, leads a team hunting particles of dark matter about a mile beneath Earth's surface. No luck so far, but Gaitskell is still hopeful. Chet Brokaw/AP hide caption

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A close-up image from the New Horizons probe of a range of mountains on Pluto, one of the highlights from space in 2015. Getty Images hide caption

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The Mars rover InSight will not launch as scheduled in March. A seismometer it was supposed to carry has experienced a series of vacuum leaks and cannot be repaired in time. Yang Lei/Xinhua/Landov hide caption

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A handout picture made available by SpaceX shows a Falcon 9 rocket landing upright at Cape Canaveral Air Force Station in Florida. SpaceX successfully returned a rocket to Earth following Monday's satellite launch after two earlier attempts failed. SpaceX/EPA/Landov hide caption

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