The simulations show another burst of chaos is due in the future “I wouldn’t lose sleep over it,” says Ghil. “They get catapulted out of the asteroid belt, some into orbits which cross the Earth’s orbit,” says Ghil. This is precisely what Ghil and his colleagues think might have happened 65 million years ago. “A burst of chaos in the Jupiter-Saturn system caused a flurry of Earth-crossing asteroids,” says Ghil. “Among them was one which struck the Earth off the coast of Central America, providing the killer blow which finished off the dinosaurs.”If Ghil and his colleagues are right, the demise of the dinosaurs cannot be attributed to an entirely random event.

As the dinosaurs grazed unawares, the great clock of the solar system went temporarily out of kilter. The dinosaurs may have been victims of an event hardwired into the dynamics of the solar system. “And they may not have been the only victims,” says Ghil.The team’s simulations reveal that another burst of planetary chaos occurred about 250 million years ago. “The most important are abrupt changes in the semi-major axis of asteroid orbits,” he says. “These would lead eventually to complete ejection of bodies from the asteroid belt.” Some of these could easily end on a collision course with Earth.The sequence of events revealed by the simulations is complex. Some asteroids suffer small jumps in the size of their semi-major axis, others large jumps Some move to smaller orbits, some to longer orbits. “A population of asteroids can drift back and forth through a succession of different orbits,” says Ghil.Crucially, bodies whose elliptical orbits become ever more elongated eventually come under the influence of the gravity of other planets and are tugged free of the asteroid belt.

Vast numbers of asteroids – ranging in size from pebbles to rocky bodies 1,000 kilometres across – circle the Sun between the orbits of Jupiter and Mars.Ghil and his colleagues simulated the effect on the asteroids of a burst of chaos in the Jupiter-Saturn system They found a wealth of effects. “The system trips over into chaos every few tens of millions of years,” says Ghil.The team’s most remarkable discovery, however, is that in a wide range of simulations in which the semi-major axis of Saturn is allowed to vary, a burst of chaos arises around 65 million years before the present. Nevertheless, it is possible to investigate the effect it would have had on other bodies in the solar system – specifically, asteroids. The asteroids are thought to be the left-over rubble of a planet which was prevented from congealing out of the “proto-planetary nebula” by the disruptive effect of Jupiter. “The timing coincides strikingly with the Cretaceous-Tertiary [geological] boundary which marks the extinction event that wiped out the dinosaurs,” says Ghil.As yet, says Ghil, it is impossible to tell how long the burst of chaos persisted. Using their digital orrery and taking this effect into account, Ghil and his colleagues discovered that as the semi-major axis of Saturn’s orbit changes, the Jupiter-Saturn system drifts back and forth between motion which is regular and motion which is totally chaotic. “What this means is that the effect of Jupiter and Saturn on the other bodies in the solar system rises to a crescendo every 1,000-odd years,” says Ghil.Until now, researchers who have used computers to simulate the long-term future of the solar system have assumed that this effect is of no consequence, guessing that over long periods of time its effect “averages out” “We had a hunch, however, that this wasn’t true,” says Ghil.