This is a beautiful sheet of 6 stamps, issued by Guinea in 2008, commemorating the Phoenix Mars Mission. Featured on the stamps are German mathematician Johannes Kepler, Danish astronomer Tycho Brahe, and the Greek mythological God of War Ares. Also included are science fiction writer of the Mars trilogy novels Kim Stanley Robinson, the Delta II space rocket, the moons of Mars Phobos & Deimos, and Dutch astronomer & physicist Christiaan Huygens. The sheet is Post Office fresh, mint never hinged, and F/VF.