History of Solar System formation and evolution hypotheses the asteroids. Terrestrial planets would have no major moons which does not account for Luna. It predicts certain observations such as the similar angular velocity of Mars and Earth with similar rotation periods and axial tilts. In this scheme there are 6 principal planets: 2 terrestrial, Venus and Earth, 2 major, Jupiter and Saturn, and 2 outer, Uranus and Neptune; and 3 lesser planets: Mercury, Mars, and Pluto. This theory has a number of problems, such as explaining the fact that the planets all orbit the Sun in the same direction, which would appear highly unlikely if they were each
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",