Orbital chaos may result in collisions between Earth and other planets – Cape Times article

12 Jun 2009 Cape Times

PARIS: A force known as orbital chaos may cause our Solar System to go haywire, leading to possible collision between Earth and Venus or Mars, according to a study released on Wednesday.

The good news is that the likelihood of such a smash-up is small, around one-in-2 500. And even then it would not happen for another 3.5 billion years.

Indeed, there is a 99 percent chance the Sun’s planets will continue to circle in an orderly pattern throughout the expected lifespan of our lifegiving star – another 5bn years, the study found. After that, the Sun will probably expand into a red giant, engulfing Earth and the other inner planets.

Astronomers have long been able to calculate the movement of planets with great accuracy hundreds, even thousands of years in advance, but peering further into the future of celestial mechanics with exactitude is still beyond our reach, said Jacques Laskar, a researcher at the Observatoire de Paris and lead author of the study.

“The most precise long-term solutions for the orbital motion of the Solar System are not valid over more than a few tens of millions of years,” he said.

Using powerful computers, Laskar and Mickael Gastineau generated numerical simulations of orbital instability over the next 5bn years.

Unlike previous models, they took into account Albert Einstein’s theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in greatly different orbital paths.
The researchers looked at 2 501 possible scenarios, 25 of which ended with a severely disrupted Solar System.

“There is one scenario in which Mars passes very close to Earth,” 794km to be exact, said Laskar. “When you come that close, it is almost the same as a collision because the planets get torn apart.”

Life on Earth, if there still were any, would almost certainly cease to exist.

Laskar and Gastineau ran an additional 200 computer models, slightly changing the path of Mars each time. All but five ended in a two-way collision involving the Sun, Earth, Mercury, Venus or Mars.

The key to all the scenarios of extreme orbital chaos was Mercury, the study, published in the journal Nature, found.

“Mercury is the trigger, and would be be the first to be destabilised because it has the smallest mass,” explained Laskar.

At some point Mercury’s orbit would get into resonance with Jupiter’s, throwing the smaller orb even more out of kilter. Once this happens, the so-called “angular momentum” from the much larger Jupiter would wreak havoc on the other inner planets’ orbits too.

“The simulations indicate Mercury, in spite of its small size, poses the greatest risk to our present order,” University of California scientist Gregory Laughlin commented in Nature.

– Sapa-AFP

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