Our understanding about how the planets in the Solar System evolved has just taken a huge leap forward with a new paper published in the journal, Icarus.
According to current theories, the dusty proto-planetary disk surrounding the sun during Solar System evolution spawned the accretion of small rocky bodies that gradually clumped together to form larger and larger asteroids. These asteroids then gradually swept up debris from the disk, eventually forming planetary bodies.
But there’s a problem, the accreting asteroids would have dropped out of solar orbit due to drag caused by the dust and gas in the sun’s accretion disk. So how did the material that makes up the asteroids and planets in our Solar System avoid being eaten by the sun?
*DISCLAIMER: The title has little to do with the research mentioned in this article and it certainly does not reflect the views of the scientists involved in this fascinating research. Linking cows with asteroids is a product of the authors questionable imagination only. The reason behind the obscure title will be revealed soon…
Although the bedrock theory of planetary formation is largely accurate, there has been some confusion as to how the accreting rocks remained in solar orbit. During their growth, asteroids would have been orbiting through clouds of dust and gas surrounding our young star, thereby experiencing drag as they traveled through the interplanetary medium. These bodies would have lost energy and then spiraled into the sun. If this was the case, there should be a lot less asteroids in the Solar System than currently observed, and there would be a huge question mark hanging over how planets formed at all.
Building on research that has been developing for the last few decades, Anders Johansen (from the Max Planck Institute for Astronomy) and a team led by Jeffrey Cuzzi (from NASA’s Ames Research Center) developed models that suggest a sudden “leap-forward” in asteroid formation, bypassing the dust drag problem.
Basically, the researchers have shown that turbulence in the proto-planetary nebula may have corralled small pieces of rock, measuring less than a meter across, in swarms (or “flocks” as termed by the New Scientist article). Eventually, these swarms became so massive, they collapsed under their mutual gravity into the center of mass. This spontaneous collapse would have been very fast in planetary evolution time scales.
Once the swarm collapsed, a far more massive single asteroid would be left over, measuring tens to hundreds of miles across. Due to it’s large mass (and therefore high momentum), the dust and gas in the proto-planetary disk would have an insignificant drag on the massive asteroid.
And now, Alessandro Morbidelli of the Côte D’Azur Observatory in Nice, France, has advanced Johansen and Cuzzi’s work by modeling our asteroid belt formation. Rather than starting the asteroid evolution simulation with small rocks, the best fit with observational data suggests asteroids measuring 60-600 miles formed spontaneously, adding weight behind the sudden swarm-collapse model.
And as for the title, it somehow spontaneously evolved in a conversation I was having with @Bellatrixlestar on Twitter about New Scientist’s choice of the word “flock” in the title of the article, “Did asteroids flock together to build planets?“:
In space, no one can hear the space cows moo…