JUPITER PROTECTING US?

Earth has good reason to be grateful to the king of the Solar System, though its influence isn't always benign

-  Andrew May

Jupiter is by far the largest planet in the Solar System, containing more than twice as much mass as the rest of the planets put together. As such, its influence on the dynamics of the Solar System is second only to the Sun itself, and it’s often said that Jupiter is the planetary ‘protector’ of Earth. But is that true, and if so, how does it work? To start with, Jupiter isn’t really that close to us. The distance from Earth to the Sun is one astronomical unit (AU), while that between the Sun and Jupiter is much bigger at around 5.2 AU. This means that Jupiter never gets closer to us than 4.2 AU, and it’s often much further away than that. And as big as Jupiter is, it still only has a thousandth of the Sun’s mass, so its direct gravitational effect on us is negligible in comparison.

The reality is that Jupiter’s influence on Earth isn’t direct, but comes about via its effect on much smaller objects in the Solar System, all the way from asteroids down to grains of dust. Continuously through its 4.6 billion years of existence, Jupiter has helped to shape the Solar System through its gravitational effects. As far as Earth is concerned, we can thank Jupiter for protecting our planet from devastating collisions in the period immediately after its birth and then giving it enough water to fill the oceans. Then it tidied up the surrounding environment by sweeping up a large proportion of the rocky debris left over from planet formation, and even today it continues to shepherd incoming comets away from the inner Solar System.