Across hundreds of known planetary systems, the same pattern holds: rocky planets orbit close to their star, gas giants orbit farther out. The explanation is straightforward. Young stars are hot. The inner disk is bathed in radiation that strips light gases away, leaving behind rock and metal. The outer disk is cooler, and gas accumulates into thick atmospheres around ice-and-rock cores. Composition maps to distance. Where you are determines what you're made of.
LHS 1903, a red dwarf observed by CHEOPS, has four planets (Science, 2026). The innermost is rocky. The second and third are gas-rich. The outermost — LHS 1903 e — is rocky again. The pattern breaks. A rocky planet orbits beyond two gas giants, in the region where standard formation models say gas should accumulate, not dissipate.
The proposed explanation inverts the spatial logic entirely. The planets didn't form simultaneously at different distances. They formed sequentially in a depleting disk. By the time the outermost planet assembled, the disk's gas had largely dissipated — not because the location was too hot, but because the supply was exhausted. The inner gas planets formed when gas was abundant. The outer rocky planet formed later, when gas was gone. The composition doesn't encode where the planet sits. It encodes when the planet formed.
The shift from where to when changes what a planet's composition means. In the spatial model, composition is a property of location — determined by temperature gradients, radiation fields, the physics of the disk at a given radius. In the temporal model, composition is a property of sequence — determined by what the disk contained at the moment of formation. The same location could produce a gas giant or a rocky world depending on when the planet assembled. Geography is a snapshot. Chronology is the process that produced the snapshot.
This dissolves a convenient simplification. Planetary science has treated the protoplanetary disk as a fixed stage on which planets assemble — regions with different temperatures, different pressures, different available materials. But a disk is not a stage. It's a resource that depletes. The conditions at a given radius change as material is consumed, accreted, and blown away. The disk at the moment the last planet forms is not the same disk that birthed the first. Composition is not a map of space. It's a fossil record of time.