"Of all known planets, Earth is as friendly to life as any planet could possibly be — or is it? If Jupiter’s orbit changes, a new study shows Earth could be more hospitable than it is today.
When a planet has a perfectly circular orbit around its star, the distance between the star and the planet never changes. Most planets, however, have "eccentric" orbits around their stars, meaning the orbit is oval-shaped. When the planet gets closer to its star, it receives more heat, affecting the climate."