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Wednesday, 27 June, 2001, 08:23 GMT 09:23 UK
Chaos clues to dino demise
Asteroid PA
An extraterrestrial impact 65 million years ago wiped out most living things
By BBC News Online's Helen Briggs

A mysterious disturbance in the forces at the heart of the Solar System could have triggered the asteroid that wiped out the dinosaurs.

This intriguing new theory has been put forward by scientists who have calculated the paths of the planets over the past 100 million years.


Our best calculations show that the dynamical state of the inner Solar System changed abruptly about 65 million years ago

Bruce Runnegar, astrobiologist
A US team believes a change in the dynamics of the Solar System caused Mercury, the Earth and Mars to veer off course.

This could have pushed a giant asteroid towards our planet, spelling downfall for most living things, 65 million years ago.

The idea has been floated by a team of astrobiologists at the University of California, Los Angeles (UCLA), based on simulations of the historical positions of the major planets.

"Our best calculations show that the dynamical state of the inner Solar System changed abruptly about 65 million years ago," said Bruce Runnegar, director of UCLA's centre for Astrobiology.

Chaos theory

The event modified the average orbit of Mercury, Mars and the Earth in significant ways, he said, possibly perturbing asteroids in the inner part of the asteroid belt and throwing one or more of them into Earth-crossing orbits.

"Thus, the ultimate cause of the K-T impact [and the demise of the dinosaurs] may have been caused by a chaos-induced change in Solar System dynamics," Dr Runnegar told BBC News Online.

Mercury Nasa
The planet Mercury could have triggered events
The basis of the theory, deduced by team members Ferenc Varadi and Michael Ghil, is chaos in the Solar System.

Under this scenario, a small shift in the orbit of one or more planets could destabilise much of the Solar System. To test their theory, the researchers simulated the orbits of the major planets, working back in history over tens of millions of years.

To their surprise, computer models pointed to a change in the dynamics of the inner Solar System at the time of the K-T (Cretaceous-Tertiary) mass extinction, about 65 million years ago, when many plants and animals suddenly became extinct.

Dr Runnegar said they were now carrying out further studies to test their theory.

"At the moment the link with the dinosaurs is based on a coincidence in time and a plausible mechanism," he added.

'Tenuous' link

The research, presented at the Earth System Processes meeting in Edinburgh, UK, has received a mixed reaction from other experts.

Professor Mark Bailey of the Armagh Observatory, Armagh, said the asteroid link appeared tenuous, but not impossible.

"[It] relies not least on the assumption that the killer projectile was an asteroid and not a comet," he told BBC News Online.


The past history of the Solar System was not as quiet as we thought - this very unusual chaotic behaviour may have happened on our doorstep

Carlos Frenk, astrophysicist
"Nevertheless, the idea that the resonant frequencies of the Solar System change chaotically on time-scales of tens to hundreds of millions of years (albeit only slowly and by relatively small amounts) is an interesting one which adds yet another wrinkle to the story of our changing Solar System."

Professor Carlos Frenk, an astrophysicist at the University of Durham, UK, said the theory appeared plausible.

"If these calculations are correct, they are very revealing of the unusual past behaviour of the Solar System," he told BBC News Online.

"The past history of the Solar System was not as quiet as we thought - this very unusual chaotic behaviour may have happened on our doorstep."

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See also:

08 Mar 01 | Sci/Tech
'Quick' demise for the dinosaurs
12 Apr 01 | Sci/Tech
Asteroids 'affected human evolution'
13 Feb 01 | Sci/Tech
In pictures: Asteroid landing
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