Astronomy Picture of the Day . ... On July 20, 1976, NASA's Viking 1 lander become the first spacecraft to land on Mars, followed weeks later by its twin robot explorer, the Viking 2 lander. ... Galileo's First Color Image of Io . ... The blue color of the nebula nearest the bright stars is caused by reflection off interstellar dust. Looking Down on Saturn . ... This picture of Saturn could not have been taken from Earth. ... A Portrait of Saturn from Titan . ... M81 in True Color . ...