This from Wikipedia:
Around 1958, Russian astrophysicist Iosif Samuilovich Shklovosky, studying the secular acceleration of Phobos’ orbital motion suggested a "thin sheet metal" structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin.
If the satellite is indeed spiraling inward as deduced from astronomical observation, then there is little alternative to the hypothesis that it is hollow and therefore martian made. The big 'if' lies in the astronomical observations; they may well be in error. Since they are based on several independent sets of measurements taken decades apart by different observers with different instruments, systematic errors may have influenced them.
The point is simply this. The idea that Phobos is artificial is nothing new. The new spin is that Philip Corso, he of The Day After Roswell fame, is the source for this. Bill Birnes, who co-authored the book with Corso tells me that Corso made no such claims.
Birnes said that he has been all through Corso’s papers and that nothing of the sort appears in them. I’m not sure why Hoagland wants to drag Corso into this, but according to Birnes, the information is in error. On this one, I think I’ll side with Birnes., Phobos