It is often said that Jupiter is our sentinel in the solar system, using its huge gravitational influence and larger diameter to orbit ratio to save the inner planets from cometary bombardment. Whether or not this is actually true, Jupiter does have a huge influence on the affairs of minor planets.
In the very beginning, it is believed that Jupiter formed as a rocky core, similar to the way the inner planets formed. Over time this core then accreted gas from the solar nebula. Finally, the planet settled into accreting gas at a low rate. This appearance of a new heavy blob in the middle of the solar system would’ve had a profound impact on the orbits of nearby bodies.
Dr Diego Turrini and colleagues at the Italian National Institute for Astrophysics in Rome performed simulations of minor planet orbits during these times. They found that during the first stage, the new core was able to deflect more and more low velocity passing objects, causing increased collisions in asteroids like Ceres and Vesta. Once in the second stage, quickly accreting gas, the mass of the planet was sufficient to deflect faster and heavier things, leading to a change in the impact scarring. Finally, the third phase occurred during the Late Heavy Bombardment period when the outer planets migrated outward, sending objects from the inner Edgeworth belt towards the inner solar system. As a result, from the cratering patterns on the surfaces of the minor planets, they can be dated to specific epochs of Jovian creation. This will be tested by NASA’s Dawn spacecraft, due to arrive at Vesta in 2011 and Ceres in 2015.
Even now Jupiter regulates minor bodies in the solar system. Between the orbits of it and Mars lies the asteroid belt, however other groups of objects exist in this region including the Greeks and Trojans, asteroids that are in orbit of the leading and trailing Lagrangian points on Jupiter’s orbit (these are points where the gravity of the planet adds to that of the Sun. The geometry and existence of these points are mirrored in any orbital systems). There are also the Hildas, these are asteroids or comets that exist in a 2:3 orbital resonance with Jupiter – for every three Jovian years, these things orbit the Sun twice.
However, Dr Katsuhito Ohtsuka of the Tokyo Meteor Network and an international team have calculated the orbits of several comets and found that they became temporary Hildas. These are comets that have the energy to escape after capture, as opposed to lower energy comets that just get captured as Hildas, Trojans, Greeks or even Moons, or comets that have too much energy or are at the right angle to simply escape.
This method allows us to trace the orbits of known satellites to get a handle on how many comets Jupiter actually catches. This in turn gives an idea of how many comets Jupiter throws into the inner solar system – which despite its sentinel status, it does as often as it captures them. This means from studies of the orbits of comets, via Jupiter, we can trace the likely impact history of our own planet.