In 1959 Shklovsky examined the orbital motion of Mars's inner satellite Phobos. He concluded that its orbit was decaying, and noted that if this decay was attributed to friction with the Martian atmosphere, then the satellite must have an exceptionally low density. In this context he voiced a suggestion that Phobos might be hollow, and possibly of artificial origin. This interpretation has since been refuted by more detailed study, but the apparent suggestion of extraterrestrial involvement caught the public imagination, though there is some disagreement as to how seriously Shklovsky intended the idea to be taken. However, Shklovsky and Carl Sagan argued for serious consideration of "paleocontact" with extraterrestrials in the early historical era, and for examination of myths and religious lore for evidence of such contact.