Cosmic Rays Cause Phantom Flashes in Astronauts' Eyes
Apollo astronauts reported seeing brief flashes and streaks of light in darkness, identified as phosphenes caused by cosmic rays passing through the visual system. The phenomenon, observed on multiple missions including Skylab, Mir, and the ISS, is attributed to charged cosmic-ray particles interacting with the eye or brain.
Supporting Evidence
Apollo 16 and 17 crews wore the Apollo Light Flash Moving Emulsion Detector to track particle paths. On Apollo 17, two of seventeen reported flashes matched heavy cosmic-ray nuclei traversing an eye. Ground experiments with heavy ion beams produced comparable flashes in dark-adapted volunteers.
Unresolved Mechanism
The biophysical mechanism remains uncertain. Proposed explanations include:
- Direct ionization of retinal tissue
- Cherenkov radiation within the eye (expected to appear bluish and diffuse, unlike the sharp white dots reported)
- Particle interaction with the optic nerve or brain
Relevance
The radiation environment causing these flashes poses a concern for long-duration space missions beyond Earth's magnetosphere, such as a trip to Mars. Understanding the effect on the central nervous system is an open problem.