All symmetric space solutions of eleven-dimensional supergravity
  We find all symmetric space solutions of eleven-dimensional supergravity completing an earlier classification by Figueroa-O'Farrill. They come in two types: AdS solutions and pp-wave solutions. We analyze the supersymmetry conditions and show that out of the 99 AdS geometries the only supersymmetric ones are the well known backgrounds arising as near-horizon limits of (intersecting) M-branes and preserving 32, 16 or 8 supersymmetries. The general form of the superisometry algebra for symmetric space backgrounds is also derived. 
Linus Wulff
hep-th