A Progress supply spacecraft undocking from the International Space Station with waste to burn up harmlessly in Earth's atmosphere.
ESA astronaut Alexander Gerst took this image during his six-month Blue Dot mission and sent it to his followers with the text: "Thank you for your service! Progress M-21M undocking from the International Space Station."
Read more about his mission at http://www.esa.int/Our_Activities/Human_Spaceflight/Blue_dot
Follow Alexander here: http://alexandergerst.esa.int/