Asteroids and meteors contain minuscule spherical grains known as chondrules, which formed when droplets of molten material cooled. Hypotheses of the formation of our solar system held that chondrules were fundamental to the beginnings of planets; as the chondrules collided with particles of dust and gas, they coalesced into protoplanets.
However, a new study led by Brandon Johnson of the Department of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology (MIT) has cast doubt on this hypothesis. According to an MIT statement, Johnson and team used a series of computer simulations to demonstrate that chondrules actually postdate the formation of the first protoplanets.
The first model examined collisions between protoplanets somewhere size between an asteroid and the Moon, looking at the locations, timing, and velocities of these impacts. This model showed that protoplanets must have formed within the first 10,000 years of the solar system’s history, prior to the formation of chondrules.
The second model was used to investigate the sort of impact that could melt material and blast it out into space. A collision happening at 2.5 kilometers per second would be powerful enough to cause this, a process known as impact jetting. During the first five million years of the solar system’s evolution, the period during which chondrules formed, such collisions transpired with sufficient frequency to generate the amount of chondrules currently observed in modern meteorites.
The third model delved into the cooling rate of chondrules. Johnson and team found that material ejected in impact jetting cooled down at 10 to 1,000 kelvins per hour, a result that agrees with previous lab-based experiments. As it turns out, chondrules are byproducts of planet formation, not a root cause.
“Then I had this ‘Eureka!’ moment where I realized that jetting during these really big impacts could possibly explain the formation of chondrules,” Johnson said. “It all fell into place.”
The new research was published in this week’s issue of the journal Nature.