Wayne Turner of South Dunedin asks :-
If the Earth and Sun's alignment was altered, say by an asteroid impact, would our lives be effected?
Alan Gilmore, an astronomer at the University of Canterbury's Mt John Observatory, responded.
The asteroids passing near the earth and other planets now are much too small to have any effect on the orbits of planets. Way back at the beginning of the solar system, four billion years ago, there were bigger rocks flying around that might have had some effect. (All evidence points to our moon being the result of a Mars-sized planet colliding with Earth.)
To have any effect on earth the asteroid would have to make a direct hit. Craters on earth show that we get hit by kilometre-sized asteroids about four times per million years on average. Such impact would cause a massive tsunami, if the asteroid hit the ocean. A hit on land would kill everything nearby and fill the air with dust. The dust would dim sunlight and affect farming globally, causing famines.
About every 100 million years we get hit by a 10-km sized asteroid. Such a hit 65 million years ago wiped out the dinosaurs and allowed mammals to become the dominant species. But a 10-km sized asteroid has no effect on earth's orbit.
If, by some magic, Earth's orbit was changed then it would definitely have an effect on the climate. The gravity of the other planets causes slow cyclic changes in the shape of the Earth's orbit. This, combined with the slow wobble of Earth's axis, causes changes in the hotness of summers and coldness of winters in the north and south and leads to ice ages. The changes are called Milankovich cycles after the mathematician who first investigated them.