French astronomers at the Observatoire de Paris have run 2,501 mathematical models of our solar system's next 5 billion years, and 25 of them end in severely disrupted orbits, often planetary collisions. These disrupted orbits don't all result in collisions with Earth, but they are all pretty disastrous for us.

In one model, Mars passes within 500 miles of Earth (that's about as far away as San Diego is from San Francisco), both planets' gravity ripping each other to pieces. In other models, either Mars or Venus careens into Earth in a fiery explosion. In all models, though, the culprit for the orbital breakdown is Mercury.

That's right, all of this possible chaos and destruction can be traced back to "orbital chaos" in Mercury's path around the sun. The models were built using old modeling techniques, but factoring in relativity effects. In the models, Mercury's orbit would start to resonate with that of Jupiter, and the combined effect would severely distort the rest of the solar system's orbits.

The odds are small (under 1% of the models have any disruption), and it wouldn't happen for billions of years. But astronomical observation shows that collisions like this might have happened before. If it did happen here, and there was anyone left to do any blaming, they should blame our diminutive near-neighbor, Mercury.

Earth-Venus smash-up possible in 3.5 billion years: study [AFP]
More concept images at Universe Today

Image artistic design: J Vidal-Madjar, provided by Nature

Astronomers were checking out a star very similar to ours located about 300 light years away, in the constellation Ares, and they noticed it was surrounded by a lot of dust. Way more dust than is in our solar system. They figured it must be a young star, and the dust just hadn't been blown away or formed into planets yet. But then someone took a closer look and realized two things: it was actually a binary star, and the system was actually very very old.

All that dust would get blown away pretty quickly unless it just appeared recently. And the only way it could have appeared so recently in such an old solar system is if two really large chunks of rock (aka planets) smashed into each other. Scientists figure it happened within the last 100,000 years or so. The awe-inspiring scale of such planetary demolition inspired one of the scientists, Tennessee State University astronomer Gregory Henry, to wax dramatic:

If any life was present on either planet, the massive collision would have wiped out everything in a matter of minutes — the ultimate extinction event. A massive disk of infrared-emitting dust circling the star provides silent testimony to this sad fate.

No one is sure what might cause planets' orbits to destabilize so drastically, but statistical projections show that there is a small chance of Mercury or Venus hitting Earth at some point in the next few million years. Which would probably look exceptionally cool for the first few minutes.

Somewhat overshadowed by all the smashing planets is the fact that this solar system is the first scientists have found in which Earth-like planets orbited a binary star. Artist's conception by: Lynette R. Cook via Science Daily.

Two Planets Suffer Violent Collision. [Science Daily]