You Need Just the Right Amount of Killer Asteroids to Promote Complex Life

by Fraser Cain on November 2, 2012

Different kinds of asteroid belts

An artist’s impression of the different configurations of asteroid belts that could occur. Image credit: NASA/ESA/A. Feild, STScI

Sure, asteroids can be planetary annihilators, scouring the surface of a world with fire and molten rock. But asteroids might also help seed a planet with the right ingredients to set up the conditions for life, and give that life encouragement to evolve more complex survival strategies.

As with all things, it’s just about balance. Too many asteroids, and you’ve got an unrelenting cosmic shooting gallery, raining fiery death from above. Too few asteroids, and complex life might not get the raw material it needs to get rolling. Life never gets that opportunity to really shake things up and evolve into more complex forms.

This conclusion comes from Rebecca Martin, a NASA Sagan Fellow from the University of Colorado in Boulder and Mario Livio of the Space Telescope Science Institute in Baltimore, Md. The researchers created a series of theoretical models based on observations of debris disks around other stars, as well as the Jupiter-sized planets discovered so far.

They found that only a fraction of the planetary systems out there have giant planets at the right locations to help create an asteroid belt of the right size. In fact, it looks like the Solar System might be rare and special when it comes to perfectly-sized asteroid belts.

“Our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet,” said Martin, the study’s lead author. “Our study suggests that our solar system may be rather special.”

There are three potential models for asteroid belt formation in other star systems.

  1. A Jupiter-sized world migrates slowly inward, disrupting the asteroid belt before it can really form. All the potential asteroids are consumed or flung out into deep space. A potential Earthlike world is deprived of the chemicals (and catastrophic incentive) to evolve complex lifeforms. That’s bad
  2. No large Jupiter-sized world forms at all, allowing the solar system to create a massive asteroid belt. Material from this enormous asteroid belt would be too punishing to Earthlike worlds for complex life to stand a chance. Also bad.
  3. A Jupiter-sized world forms in the outer solar system, and only moves in a little, preventing an overly large asteroid belt from forming. There are still enough asteroids out there to seed an Earthlike world with chemicals and evolutionary encouragement, but not enough to set its progress back. That’s us!

To come to this conclusion, Martin and Livio created models of protoplanetary disks around various stars, and then watched what would happen with various Jupiter-sized planets. They compared their models to 90 protoplanetary disks that have been discovered so far by NASA’s Spitzer Space Telescope, and 520 giant planets found orbiting other stars.

So far, only 4% of the systems they’ve observed have the right combination of a compact asteroid belt with a Jupiter-sized planet nearby. This gives researchers a very specific configuration of asteroid belt and planetary arrangement to look for when searching for worlds that could contain complex life.

Original Source: NASA News Release


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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