Orbital mirror megastructures are a proposed class of passive technosignature: giant reflective structures placed in orbit around habitable-zone exoplanets — particularly tidally-locked planets around M-dwarf stars — to redirect starlight and offset a permanent day/night divide. Distinct from Dyson-sphere-style infrared-excess signatures (which detect waste heat re-radiation around the host star), this concept centers on detectable orbital mechanics of mirrors around a planet.
Key Physics
A 2026 study by shauna-sallmen and eric-korpela modeled the core engineering problem: radiation pressure from starlight (“photon push,” the same effect exploited in solar sailing) destabilizes lightweight, high-surface-area mirrors over time, requiring either active station-keeping or careful orbital design to remain stable long-term.
Using the REBOUND N-body simulator (1000 kg, 1 km² mirror; 2/3/10 planetary radii; four orbital configurations; 1,000 trials each), the authors found:
- Mirrors around M-dwarf-hosted planets survive longest.
- Retrograde orbits outlast prograde ones.
- Mirrors closer to their host planet, or orbiting planets farther from their star, survive longest, because planetary gravity dominates over radiation pressure.
The authors argue that the fine-tuning required for a stable configuration is very unlikely to arise naturally — making a detected stable mirror megastructure a strong technosignature candidate for next-generation telescopes.
This substantiates an earlier speculative thread on “detectable megamirrors around exoplanets” raised at AbSciCon26 (src-abscicon26-media-tips-2-2026-05) with concrete orbital modeling.