Scientists have long believed that meteors were fundamental to the origins of our planets. Meteors contain minuscule spherical grains known as chondrules, and many have believed these chondrules collided with particles of dust and gas coalescing into protoplanets. However, according to a new study published this week in the journal Nature, this hypothesis may not be true.
In a statement from MIT, lead professor of the study Brandon Johnson and his team used a series of computer simulations to demonstrate that chondrules actually postdate the formation of the first protoplanets in our solar system. Chondrules, in fact, are now believed to have been created by the collision of much larger moon-sized bodies.
"Once the two bodies collide, a very small amount of material is shocked up to high temperature, to the point where it can melt," Johnson says. "Then this really hot material shoots out from the collision point."
Some of the chondrules would then attach to larger objects like meteors, and some of these objects would then ultimately impact the Earth.
"This tells us that meteorites aren't actually representative of the material that formed planets - they're these smaller fractions of material that are the byproduct of planet formation," Johnson says. "But it also tells us the early solar system was more violent than we expected: You had these massive sprays of molten material getting ejected out from these really big impacts. It's an extreme process."
The first model examined collisions between protoplanets ranging in size from a typical asteroid and the Moon, looking at the locations, timing and velocities of these impacts. The model showed that the protoplanets must have formed within the first 10,000 years of the solar system's history, long before the formation of chondrules.
The second model investigated the type of impact that could melt material and blast it out into space. Researchers found that a collision happening at 2.5 kilometers per second would be sufficient. During the first five million years of our solar system, when the chondrules formed, these collisions occurred frequently enough to generate the amount of chondrules currently observed in meteorites.
The third model examined the cooling rates of chondrules. The team discovered that material ejected by an impact would cool down at 10 to 1,000 kelvins an hour. As it turns out, chondrules are the byproducts of planet formation and not the root cause of the formation of a planet.
Fred Ciesla, an associate professor of planetary science at the University of Chicago, touched on the implications of these findings saying that, "If this finding is correct, then it would suggest that chondrites are not good analogs for the building blocks of the Earth and other planets."
Indeed scientists may now have to revise their thinking on asteroids and the formations of the planets in our solar system, and at the very least they must now alter the types of asteroids they should study when it comes to planetary formation.
