Large Planetary Bodies Impacts : a first order analysis

We review situations where large scale impacts between bodies of planetary sizes may arise, or have been invoked to explain structures that seem to have arisen after such impacts. We are interested in the orbital variations for the special case the impacting objects is in some sense absorbed by the impacted body, whose mass is larger. Under rather strong simplifications we calculate such variations using the condition of conservation of either the total energy or the total momentum and Kepler's third equation. Results are discussed in terms also of such events having possibly taken place in the solar system.