What happens when planets collide

In a few billion years there could be collisions between planets in the inner solar system - but fortunately, the likelihood of this is low

Mars collides with the earth

Paris (France) - The planets in the solar system seem to move with the regularity of clockwork - but the impression is deceptive. With their forces of attraction, the planets disturb each other's orbits and can plunge the whole system into chaos. In the journal "Nature", French researchers report on detailed simulations of the future of the solar system. Collisions between Mercury, Venus, Earth and Mars are then possible in a few billion years, but fortunately very unlikely.

Last year, Jaques Laskar from the Paris Observatory had already shown that a resonance of the orbital movements of Mercury and Jupiter can lengthen the orbit of the planet closest to the Sun and put it on a collision course with Venus. "But these conclusions were based on averaged equations, which are not very precise, especially in the area of ​​the collision," says the astronomer. Together with his colleague Mickael Gastineau, he has now carried out a total of 2501 extremely accurate simulations of the future of our solar system. Each of these simulations is based on a slightly different starting situation, in which the initial positions of the planet Mercury differ from each other by only one meter.

In just twenty of the scenarios examined, i.e. about one percent of the cases, the orbit of Mercury actually expands under the influence of Jupiter in such a way that it can overlap with the orbits of the other planets and thus destabilize the inner solar system. As a result, Mercury can plunge into the sun or collide with Venus.

But the earth can also be affected by the resulting chaos: In one of the simulations there will be close encounters between Mars and earth in around 3.3 billion years. Laskar and Gastineau examined this scenario in more detail with a further refinement of the initial conditions. Afterwards, these encounters can lead to collisions between Earth and Mars, as well as between Earth and Venus or Mercury. Another possibility is that Mars will be thrown out of the solar system.