Planet formation theory predicts a simple radial gradient: rocky worlds close in (where stellar radiation strips gas), gas-rich worlds farther out (where conditions allow thick atmospheres). The LHS 1903 system, 116 light-years away in Lynx, violates this in the most awkward way possible. Its four planets go: rocky, gaseous, gaseous, rocky. The innermost and outermost are small rocky worlds. The two in between are mini-Neptunes, six times Earth's mass and twice its diameter. An inside-out sandwich.
ESA's CHEOPS mission detected the fourth planet, LHS 1903 e, in the outer orbit — exactly where a gas giant or at least a gas dwarf should sit. Instead, it's bare rock. The radiation stripping explanation works for the inner rocky planet but fails completely for the outer one, which is far enough from the star that a thick atmosphere should have survived.
The proposed explanation: timing. LHS 1903 e formed late — after the protoplanetary gas disk had already dissipated. The inner planets formed together while gas was abundant; the two middle ones accreted thick envelopes. By the time the outermost world assembled, there was no gas left to capture. The material was there (solids persist after gas disperses), but the atmospheric ingredient had expired.
The structural lesson is about sequence rather than geography. The same location in the same disk produces a completely different planet depending on when formation occurs, not just where. A rocky world in an outer orbit isn't evidence that conditions prevented gas accretion — it's evidence that the planet showed up after the gas was gone. The system isn't anomalous because of spatial arrangement. It's anomalous because of temporal arrangement. Formation order is as load-bearing as formation position, and the models that treat the disk as a static snapshot miss exactly this.
The planet shouldn't be there. It formed after the party ended, and found only the furniture.