With Sergei Kopeikin and George Kaplan, Michael Efroimsky co-authored a book[1] on the relativistic celestial mechanics of the Solar System.
With Benoit Noyelles, Julien Frouard and Valeri V. Makarov, Michael Efroimsky co-authored a theory [2] explaining the origin of the present state of rotation of the planet Mercury, a so-called 3:2 spin-orbit resonance.
With Amirhossein Bagheri, Amir Khan, and other colleagues, Michael Efroimsky co-authored a theory explaining the origin and orbital evolution of Phobos and Deimos, the satellites of Mars.
[4] He demonstrated that if Nerio were large enough, perhaps a third the mass of our Moon, its gravitational pull on the young and still soft Mars was sufficient to create an asymmetric tidal bulge, which later fossilised and made the equator noncircular, resulting in the planet's triaxial shape.
Efroimsky also hypothesised that the tips of that bulge were more prone to subsequent volcanic and tectonic activity than the rest of the Martian surface, leading to the development of both Tharsis and the highlands on the side opposite to it.