Every week, we bring you more stories on how the solar system formed. Or how other planetary systems form. Or are forming. So much formation. And I keep saying we’ll never figure it out because there are too many variables and nothing seems to be a standard.

Here we go again. This time, a new paper in Science looks at how our solar system formed in a two-step process that split up the planets into dry terrestrial planets and wet outer planets. I’m using the terms dry and wet rather loosely, I know. Lead author Tim Tichtenberg explains: Inner Solar System planetesimals became very hot, developed internal magma oceans, quickly formed iron cores, and degassed their initial volatile content, which eventually resulted in dry planet compositions. In comparison, outer Solar System planetesimals formed later and therefore experienced substantially less internal heating and therefore limited iron core formation, and volatile release.

Essentially, we had two distinct formation episodes in our solar system: the first had an early onset and took a long time, building the inner solar system slowly enough to allow rocky planets to come together. The second occurred later and much more quickly, with wetter particles beyond the snow line, giving rise to quickly spun up gas giants and smaller terrestrial bodies.

Tichtenberg further noted: The early-formed and dry inner Solar System and the later-formed and wet outer Solar System were therefore set on two different evolutionary paths very early on in their history. This opens new avenues to understand the origins of the earliest atmospheres of Earth-like planets and the place of the Solar System within the context of the exoplanetary census across the galaxy.

This work gives a very broad overview of our solar system’s formation process that could apply to other planetary systems, but I still don’t think it’s the end result we’re looking for. More research is needed, as always, before we get a complete picture that covers more of the nuances of planetary system formation.

More Information

EurekaAlert article

“Bifurcation of planetary building blocks during Solar System formation,” Tim Lichtenberg, 2021 January 22, Science