The traditional belief that Jupiter acts as a celestial shield, deflecting asteroids and comets away from the inner Solar System, has been challenged by the first in a series of studies evaluating the impact risk to the Earth posed by different groups of object.

On Friday 24th August at the European Planetary Science Congress in Potsdam, Dr Jonathan Horner presented a study of the impact hazard posed to Earth by the Centaurs, the parent population of the Jupiter Family of comets (JFCs). The results show that the presence of a Jupiter-like planet in the Solar System does not necessarily lead to a lower impact rate at the Earth.

Dr Horner, from the UK's Open University (OU), said, "The idea that a Jupiter-like planet plays an important role in lessening the impact risk on potentially habitable planets is a common belief but there has only really been one study done on this in the past, which looked at the hazard due to the Long Period Comets. We are carrying out an ongoing series of studies of the impact risks in planetary systems, starting off by looking at our own Solar System, since we know the most about it!"

The team at the OU developed a computer model that could track the paths of 100,000 Centaurs around the Solar System over 10 million years. The simulation was run five times: once with Jupiter at its current mass, once without a Jupiter, and then with planets of three-quarters, a half and a quarter the mass of Jupiter (for comparison, Saturn is about a third of the mass of Jupiter). The team found that the impact rate in a Solar System with a planet like our Jupiter is about comparable to the case where there is no Jupiter at all. However, when the mass of Jupiter was between these two extremes, the Earth suffered an increased number of impacts from the JFCs.

 Source : Science Daily