'G': This image of Pinaki Island was captured by astronauts on the International Space Station (left). 'H': The Operational Land Imager on Landsat 8 acquired this image of rivers running through colorful ridges in southwestern Kyrgyzstan (right). He asked others to let him know if they find anything that looks similar to a letter in the alphabet. ‘Send a link to what you’ve found, and explain what letter or other typographical mark you think you see'