The Lunar Threshold / El Umbral Lunar

Permanent human presence on the Moon is moving from plan to construction, yet no international mechanism coordinates the actors arriving at its south pole, and no shared ethical framework governs how human bodies will be adapted to live there. This paper argues that both gaps share a structure and call for a single principle. Among currently contemplated settlement destinations, the Moon is the nearest environment in which sustained human presence can be combined with comparatively short return to Earth: Earth is visible in its sky, signal delay is about 1.3 seconds and travel takes days. It is therefore a threshold where commitments can still be revised. From this the paper derives a principle of reversibility: no arrangement that forecloses future options, whether over shared lunar sites or over a person's own body, should become irreversible before it has been tested in reversible form under conditions that still allow return. The principle is grounded in the economics of irreversibility and option value, in work on transformative experience, and in the ethics of the future self. At the institutional level it yields use concessions that decay when unused, polar commons with rotating access, a life floor independent of flag or employer, and a witness institution that records without governing. At the bodily level it yields a phased training protocol, a notion of lived consent and three equally recognized outcomes for participants. The paper situates both applications within current space law and the ongoing work of the UN Action Team on Lunar Activities Consultation, addresses six objections, and proposes a research agenda.