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IN SPACE - JULY 17: (EDITORIAL USE ONLY) In this handout photo provided by the European Space Agency (ESA) on July 17, 2014, German ESA astronaut Alexander Gerst took this image of the Earth reflecting light from the sun whilst aboard the International Space Station (ISS). Gerst returned to earth on November 10, 2014 after spending six months on the International Space Station completing an extensive scientific programme, known as the 'Blue Dot' mission (after astronomer Carl Sagan's description of Earth, as seen on a photograph taken by the Voyager probe from six billion kilometres away). (Photo by Alexander Gerst / ESA via Getty Images)

IN SPACE - JULY 17: (EDITORIAL USE ONLY) In this handout photo provided by the European Space Agency (ESA) on July 17, 2014, German ESA astronaut Alexander Gerst took this image of the Earth reflecting light from the sun whilst aboard the International Space Station (ISS). Gerst returned to earth on November 10, 2014 after spending six months on the International Space Station completing an extensive scientific programme, known as the 'Blue Dot' mission (after astronomer Carl Sagan's description of Earth, as seen on a photograph taken by the Voyager probe from six billion kilometres away). (Photo by Alexander Gerst / ESA via Getty Images)