The Phobos monolith is a large rock on the surface of Mars' moon Phobos.[1] It is a boulder, about 85 m (279 ft) across and 90 m (300 ft) tall.[2][3] A monolith is a geological feature consisting of a single massive piece of rock. Monoliths also occur naturally on Earth, but it has been suggested that the Phobos monolith may be a piece of impact ejecta. The monolith is a bright object near Stickney crater, described as a "building sized" boulder, which casts a prominent shadow.[4][5] It was discovered by Efrain Palermo, who did extensive surveys of Martian probe imagery, and later confirmed by Lan Fleming, an imaging sub-contractor at NASA Johnson Space Center.[6]
The general vicinity of the monolith is a proposed landing site by Optech and the Mars Institute, for a robotic mission to Phobos known as PRIME (Phobos Reconnaissance and International Mars Exploration).[4] The PRIME mission would be composed of an orbiter and lander, and each would carry four instruments designed to study various aspects of Phobos' geology.[7] At present, PRIME has not been funded and does not have a projected launch date. Former astronaut Buzz Aldrin has spoken about the Phobos monolith and his support for a mission to Phobos.[8]
The object appears in Mars Global Surveyor images SP2-52603[9] and SP2-55103,[10] dated 1998. The object is unrelated to another monolith located on the surface of Mars, which NASA noted as an example of a common surface feature in that region.[11]