Nautilus Constellation Targets Statistical Tracking of Exoplanet Atmosphere Evolution Over Billion-Year Timescales

The white paper identifies four objectives: determining sub-Neptune and super-Earth formation timescales, quantifying temporal changes in atmospheric escape, tracking shifts in atmospheric composition, and detecting the onset of helium-dominated worlds. These require simultaneous high-resolution spectroscopy over broad wavelengths with large collecting area, capabilities absent from current facilities like JWST or HST that limit statistical samples to narrow age ranges. Current demographic data already show young planets differ in radius and density from mature counterparts, implying rapid early evolution driven by photoevaporation and core-powered mass loss. Nautilus's parallelized units would enable population-level studies connecting disk dispersal to solar-system-like architectures.

Existing facilities cannot deliver the required sample sizes or wavelength coverage for age-stratified atmospheric retrievals, leaving causal links between formation location, migration, and final composition untested. The proposal draws on emerging evidence from young transiting planets and disk observations to argue that mean molecular weight increases and C/O decreases as atmospheres cool and contract. Parallel observations across dozens of targets would isolate these processes at the population level.

A dedicated future observatory would close the observational gap between exoplanet demographics and solar-system origins by providing the first age-resolved atmospheric census. Selection in the next astrophysics decadal survey would be required to advance from concept to mission formulation within the next decade.