Asteroid belts like the one between Mars and Jupiter are rare beyond our solar system, and studies indicate that they may be contributing to the galaxy's dearth of life.
According to a new study, having the right kind of asteroid belt in a solar system could be the key to finding intelligent life in the universe. NASA and the UK's Royal Astronomical Society have been studying the role of asteroid belts in the evolution of life on Earth, as well as in the wider universe.
Researchers found that an asteroid belt plays a very important role in the development of life, as its material seeds rocky planets with water and complex chemicals without overwhelming the worlds with a barrage of violent impacts. Fewer than four percent of known alien solar systems are likely to have such an asteroid belt.
"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. Our study suggests that our solar system may be rather special," said lead author Rebecca Martin, a NASA Sagan Fellow from the University of Colorado in Boulder, according to Space.com.
The early Earth likely got huge amounts of water and organic compounds from space rocks and comets, and the theory of punctuated equilibrium indicates that occasional impacts disrupting the status quo and opening up new niches may have helped accelerate the rate of biological evolution. Consequently, researchers said that a "just-right" asteroid belt may be essential to the evolution of complex life forms on rocky worlds.
The asteroid belt of our solar system formed where it did because Jupiter's gravitational pull prevented the material in the region from clustering together to create a planet. According to researchers, the belt looks as it currently does because long ago Jupiter moved just the right amount.
"To have such ideal conditions you need a giant planet like Jupiter that is just outside the asteroid belt [and] that migrated a little bit, but not through the belt," said study co-author Mario Livio of the Space Telescope Science Institute in Baltimore, as cited by Space.com.
"If a large planet like Jupiter migrates through the belt, it would scatter the material. If, on the other hand, a large planet did not migrate at all, that, too, is not good because the asteroid belt would be too massive. There would be so much bombardment from asteroids that life may never evolve," Livio explained.
Our own asteroid belt is near the solar system's "snow line," i.e. the point beyond which it is cold enough for volatile substances like water to stay intact and remain solid. Based on this fact, Martin and Livio reasoned that alien belts are likely to be located near their system's snow lines as well.
Examining other solar systems to determine whether similar conditions could be found elsewhere, the researchers found that only 19 of the 520 giant planets studies were outside the snow line, and only 4 percent of those have the kind of compact asteroid belt found in our system.
Based on this asteroid belt scenario, efforts should focus on looking for complex life in systems that have a giant planet outside the snow line, noted Livio.
