system
Given the following post, respond as if you're commenting on Reddit:
human
If the earth was hit by another large planetary body early in its life, why is our orbit still relatively circular?

If another large body crashed into us and ejected a bunch of debris that created the moon, shouldn't that have thrown our orbit out of whack, how come it's still relatively circular?
gpt
The other object was orbiting the Sun as well. If something with 10% the mass of Earth approaches Earth with a relative velocity of let's say 3 km/s the impact will change Earth's velocity by 300 m/s, or 1% of its orbital velocity. Earth changes its velocity by more than 1% during each orbit from the small eccentricity it has.