In 2003, Donald Pettit, a NASA astronaut, sprinkled some salt into a ziplock bag for an experiment. Pettit was living on the International Space Station, about 200 miles above Earth. The station was just a few years old then, and astronauts were keen to see how stuff reacted in microgravity.
Pettit gave the bag a good shake. When he stopped, the salt crystals were suspended like tiny flakes in a snow globe. Then there was movement. The particles began bumping into each other. They stuck to each other, forming small chunks, which then collided with other chunks. Within seconds, the crystals had coalesced into one big clump. When Pettit shook the bag again, the clump refused to break apart.
With a plastic bag and some salt, Pettit had created a tiny model of planet formation.
The planets in our solar system and beyond all started out this way, as tiny particles in the cloud of dust and gas left behind from the violent birth of their parent stars. As they bumped into each other to form larger and larger chunks, their gravity attracted even more building material. After millions of years, they became massive worlds.
Astronomers are still trying to understand this process. A team of European astronomers recently aimed one of the world’s most powerful ground-based telescopes at a young star and crossed their fingers. If they looked long enough, perhaps they could catch a glimpse of a baby planet swirling into shape out of the cosmic fog.