Note that there may be configurations of planet pairs you can think of where you may require more than one of the three points above to be true. When an object of near-planetary mass or more collides with a rocky planet, the force of the impact will melt the planet's surface, turning it into a hot ball of molten rock and iron and vaporizing the planet's surface liquids. The planet will take a long time to cool down, after which its atmospheric composition and other parameters may have changed. If you collide an asteroid made of ice with a planet, its sea level may rise.
