The rocky planets closest to the sun are made up of very different materials than the gas giants in the outer solar system. That’s because billions of years ago, our baby solar system was divided in two by a cosmic gatekeeper that prevented materials in the inner and outer regions from mixing.
It turns out that gatekeeper was a ring of dust and gas, according to a new study. The fence, or “Great Divide,” a term coined by the authors, is now mostly empty space just inside Jupiter’s orbit.
About two decades ago, chemists realized that the building blocks of planets — asteroid-size planetesimals or much smaller “pebbles” — had very different compositions depending on their distance from the sun. The pebbles that built up the outer, or “jovian,” planets contained higher concentrations of organic molecules such as carbon and volatiles, or ices and gases, than those that built up the “terrestrial” planets closer to the sun, such as Earth and Mars.