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January 15, 2004 - Mars rover Spirit lands safely on Mars and begins to send back data that transforms our understanding of the red planet.
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July 20, 2005 - On the anniversary of one of the greatest human accomplishments, this doodle celebrated the lunar landing
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January 4, 2006 - Though not real bumps on your monitor, the transformation of the Google logo to a Braille doodle honors the creator of the lettering system, Louis Braille
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October 3, 2007 - 50 years after it created uncomfortable tension in the Cold War, the technological accomplishment of Sputnik - the first artificial satellite - is no less significant
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September 27, 2008 - For their own 10th anniversary, Google reverted to their original logo and celebrated with a cake
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October 7, 2009 - Commemorating the invention of the barcode, Google embeds its name in the most cryptic doodle yet. Go ahead, use a barcode scanner on it!
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November 4-10, 2009 - The Muppets of Sesame Street took over Google doodles to create a dozen different variations in celebration of their 40th anniversary
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January 4, 2010 - Sir Isaac Newton's 367th birthday. When the apple falls from the tree, it demonstrates the first HTML5-powered animated doodle
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May 21, 2010 - A few months later Google launched a fully interactive PAC-MAN game inside the doodle. One estimate put the cost to the economy at $120 million due to lost work hours
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October 8, 2010 - Using a video instead of animated image or HTML5, this doodle celebrates the 70th birthday of John Lennon with a logo build to his song, "Imagine"