(06-10) 20:40 PDT -- From chaos we all began, and to chaos we'll all return, but not for a very, very long time - 5 billion years or so, more or less.
In the journal Nature today, two French scientists, using arcane mathematical models, predict that in the distant future, the Earth and planet after planet will collide with each other as an inevitable part of the solar system's long-term evolution.
For many millennia, the scientists say, the orbits of the solar system's eight planets will remain stable, just as they are today, but eventually small eccentricities in their flight paths around the sun could cause Mercury, Mars, Venus and Earth to smash into each other, either one at a time or all at once - the ultimate chaotic disaster.
But because that predicted chaos is so far in the future, the scenario actually "sounds a note of definite cheer," and the planets will be safe for a long, long time, said Gregory Laughlin, an astrophysicist at UC Santa Cruz whose written commentary accompanies the French scientists' report in Nature.
Inner planets stable
For one thing, Laughlin noted, the prophets of eventual doom - astronomer Jacques Laskar and computer engineer Mickael Gastineau of France's Paris Observatory - calculate that the odds are 99-to-1 that the orbits of the four inner planets - Mercury, Venus, Earth and Mars - will remain stable for the full 5 billion years.
The time frame coincides with accepted theory that by the end of that same 5 billion years the sun will have burned up its hydrogen and in a cooler state will inflate itself into what's called a red giant star, engulfing the entire inner solar system while the planets are still colliding.
So, either way, the planets of the inner solar system are safe for another 5 billion years, according to Laughlin.
On the other hand, the great "gas giants" of the outer solar system - Jupiter, Saturn, Uranus and Neptune - are extremely stable in their orbits, so they could remain where they are for a much longer time - a billion billion years or so - that's a 1 with 18 zeroes - according to Laughlin.
In an e-mail from Paris, Laskar said he and Gastineau, who wrote the computer codes for their calculations, sifted through 2,501 possible constructions of planetary orbits in the far future and found that "only a single one led to possible encounters of Earth and either Venus or Mars." But other scenarios in the computer calculations by Laskar and Gastineau depicted a variety of other inner solar system collisions, including Mercury smashing into Venus and Mercury even colliding with the sun, Laskar said.
'Finally brings closure'
The scientists and their calculation of the solar system's ultimate future "finally brings closure to one of the most illustrious and long-running problems in astronomy," Laughlin said, referring to the mystery of the solar system's ultimate fate. "With 99 percent certainty, we can rely on the clockwork of the celestial rhythm - but with the remaining 1 percent, we are afforded a vicarious thrill of danger."
Erik Asphaug, a planetary scientist at UC Santa Cruz, has long studied the tumultuous time nearly 5 billion years ago, when the huge ring of dust and rocks surrounding the early sun was gradually clumping into the first planets. Asphaug said the French scientists' findings are by no means outlandish.
"It's not a crazy idea that our planets now may be in the second stage in the evolution of the solar system," he said.
As to the past, Asphaug and his colleagues published a paper in Nature three years ago entitled "Hit-and-run planetary collisions" that pictured a time around 4.6 billion years ago when hundreds of "planetary embryos" as large as Mars were colliding with each other and with Jupiter at random speeds.
Chaos period
Ultimately, the Earth and the other three inner planets formed, while the remaining junk became the rocky objects of the asteroid belt - all during a time period of 10 million to 100 million years, Asphaug and his colleagues calculated.
Asphaug and Robin Canup of the Southwest Research Institute in Boulder, Colo., have also proposed that during that time of chaos between 4.6 billion and 4.5 billion years ago, an unknown giant object - perhaps the size of Mars - collided with the partly formed Earth and ripped off a huge chunk of it - a chunk that became the iron-poor moon while the Earth, still partially melted from the impact, assumed its present shape and resumed its stately orbit about the sun - the orbit we know today.
from San Francisco Chronicle
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