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
Climate of Uranus darkness for many years indicates that near equinox Uranus entered a period of elevated weather activity. The tracking of numerous cloud features allowed determination of zonal winds blowing in the upper troposphere of Uranus. At the equator winds are retrograde, which means that they blow in the reverse direction to the planetary rotation. Their speeds are from −100 to −50 m/s. Wind speeds increase with the distance from the equator, reaching zero values near ±20° latitude, where the troposphere's temperature minimum is located. Closer to the poles, the winds shift to a prograde direction, flowing with its rotation. Wind speeds