In February, NASA's STEREO probes, two observatories that were launched in 2006 to survey the sun, reached opposite ends of the sun and thus, were able to give scientists (and the rest of us!) a never-before-seen view of the far side of the star at the center of our solar system. The composite image above was captured on June 1, 2011, and according to NASA, "is the first complete image of the solar far side, the half of the sun invisible from Earth." Click here for more on the STEREO probes.
While it's not a "discovery," per se, it's a milestone that will no doubt lead to many new findings about the smallest and innermost planet in our solar system. In March, after a 6 1/2-year, 4.9 billion mile journey, NASA's Messenger spacecraft reached Mercury's orbit. Messenger, the first spacecraf...
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