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Future Collisions in the Solar System

Ever since Newton, astronomers have been trying to understand the gravitational interactions of planets to predict their orbits. The movements of the planets in our Solar System were thought to be mostly stable and predictable, with slight but regular modifications. This changed in 1989, when French astronomer Jacques Laskar demonstrated that the Solar System's inner planetary orbits were in fact largely chaotic, and that this could even lead to a collision between Mercury and Venus on billion-year time frames. Could this happen before our sun begins to die, in 5 billion years?
future collisions

© IMCCE (Observatoire de Paris/UPMC/CNRS)

Example of long-term evolution of the planetary orbits: Mercury (white), Venus (green), Earth (blue), Mars (red). Time is indicated in thousands of years (kyr). Various scenarios show possible collisions between the planets.

To find out, Laskar,1 together with fellow researcher Mickaël Gastineau, recently used the new Jade supercomputer at the French National Computing Center to do the 7 million hours of calculations needed to chart the motions of planets in 2500 different scenarios over the next 5 billion years.2 Jade took only five months to do the maths. In each simulation, minute changes were made to Mercury's orbit (0.38 mm sequentially), taking into account the moon, the eight planets and Pluto's contributions, as well as Einstein's general relativity. All simulations start the same, but after tens of millions of years, variations begin to accumulate and trajectories start to diverge. In most cases, the Solar System is unaffected: Orbits deform and precess (a slow rotation of the ellipse in space) through the planets' gravitational interactions but without any of them being ejected or colliding. However, in about 1% of cases, Mercury's eccentricity (the elongation of its orbit) increases dramatically–up to 0.9. This may lead, in one case, to an increase in Mars' eccentricity, which in turn results in a total destabilization of the Solar System approximately 3.4 billion years from now. In this latter scenario, Mars has a 2.5% chance of being ejected, whereas the other solutions lead to planets colliding with each other, and a 24% chance of the Earth being involved in such a collision.
Astronomers are quite sure that a collision could happen in less than five billion years. “The next step is to try to predict the earliest date at which a collision with Earth could occur,” concludes Laskar.

Marion Girault-Rime

Notes :

1. Institut de mécanique céleste et de calcul des éphémérides (CNRS / Observatoire de Paris / Université Paris-VI).
2. J. Laskar et al., “Existence of collisional trajectories of Mercury, Mars and Venus with the Earth,” Nature, 2009. 459: 817-9.

Contacts :

Jacques Laskar,
IMCCE, Paris.


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