Every planet formed from the same disk of material, yet became radically different

Sobel traces the solar system's origin to a rotating cloud of gas and dust left from an earlier generation of stars, out of which the sun condensed roughly five billion years ago while leftover material flattened into a disk and clumped into progressively larger planetesimals. The striking fact she emphasizes is that despite this common origin, the resulting planets diverged enormously depending almost entirely on distance from the newborn sun.

Close to the sun, where temperatures were too high for volatile compounds like water and gas to condense, only dense, rocky, metallic material survived, producing small, solid inner planets like Earth and Mercury. Farther out, where it was cold enough for ices and gases to persist, growing planets accumulated enormous quantities of hydrogen and helium, producing gas giants like Jupiter and Saturn many times more massive than any inner planet.

Sobel frames this divergence as a lesson in how one variable, temperature-driven distance, produced a solar system of startling variety rather than a set of similar worlds.

*Takeaway: dramatic differences in outcome don't always require different starting materials — sometimes one consistent variable is enough.