The Phobos Monolith

Phobos is the larger of Mars's two moons and some 27 kilometres long. In a Mars Global Surveyor frame from 1998 one object near the crater Stickney stands out from everything else: a bright block the telling puts at 85 to 90 metres across and about as tall, throwing a long triangular shadow across the surface. The telling holds that nothing else on Phobos is nearly as large, that its reflectivity is unlike the ground around it, and that the proposed PRIME mission of 2008 chose it as a candidate landing site. The lander was to set down within an arm's length of the block and analyse fresh rock on the spot.

What is on the record

One claimant on one channel, and the claimant is Buzz Aldrin, who imaged nothing. His contribution is a remark on C-SPAN in July 2009 that there is a monolith on the moon of Mars and that when people find out they will ask who put it there. His own answer, on the tape, is that the universe put it there. Or God, if you choose. Outside the archive's holdings the object is a boulder. The 1998 frame is MOC image SP2-55103, taken on 12 September 1998, and JPL's own caption for it, published in 2003, calls the object a very large boulder about 85 metres across. HiRISE re-imaged Phobos in 2008 without comment on it. The reading of record is a block of Stickney ejecta. The PRIME proposal is real and unflown, and its own text calls the object a boulder.

Why it sits where it does

The case grades L0, a single account, and the account is a quotation. What it is, is a boulder on the record; whether that closes the question is not resolved here.