Comparative planetary science closest analogue is the Pluto-Charon system, though its axial tilt is completely different. Both our Moon and Charon are hypothesized to have formed via giant impacts. Giant impacts are hypothesized to account for both the tilt of Uranus, and the retrograde rotation of Venus. Giant impacts are also candidates for the Mars ocean hypothesis, and the high density of Mercury. Most giant planets (except Neptune) have retinues of moons, rings, ring shepherds, and moon Trojans analogous to mini-solar systems. These systems are postulated to have accreted from analogous gas clouds, and possibly with analogous migrations during their formation periods. The
Upsilon Andromedae from the star. Both of these planets are in more eccentric orbits than any of the planets in the Solar System (including Pluto). Upsilon Andromedae d resides in the system's habitable zone. The orbital parameters of this three planet system have been fully determined. The system is not coplanar, with each other or with the stellar rotation, as in our solar system. Simulations shows that the measured configuration of the planets produces indeed stable orbits for at least 100 million years, where planets "b" and "d" remain roughly coplanar. General relativity is expected to have strong effects on planet "b",