The key to forming a planet could be found in some of the tiniest pieces of space debris—glassy beads the size of grains of sand that are known as chondrules. According to simulations developed in part by researchers at the Museum, asteroid-like objects known as planetesimals sweep up these glassy grains, growing into planets as they accumulate more and more dusty particles. The results of the simulations, carried out with collaborators at Lund University in Sweden and elsewhere, were published today in the journal Science Advances.
“The big question is, ‘How did the planets come to be?’” said Mordecai-Mark Mac Low, a curator in the American Museum of Natural History’s Department of Astrophysics and an author on the paper. “When the solar system first started forming, the largest solids were sub-micron dust. The challenge is to figure out how all of that dust was gathered up into planet-building objects that then formed the diversity of planets and other smaller bodies that we see today.”
Planets start out small, as dust particles in the disk of gas and dust surrounding a young star collide and stick together to form dust bunnies, then pebbles, then boulders. However, models show that when those boulders get larger than a person, they begin to orbit faster than the surrounding gas. The resulting headwind brakes them in their orbit, so that they drift into their parent star within about 100 orbits. In addition, fast-moving boulders break apart, rather than sticking together, when they collide. So how do some of these objects stick around long enough to grow into planets?