To date, the phase transition of ordinary proton-disordered ice to proton-ordered ice has been assumed to require an extremely long time (>10(4) year). However we have observed, by cryogenic transmission electron microscopy, the phase transition from a sphalerite proton-disordered phase (ice I-c) to an orthorhombic proton-ordered phase (ice XI) in a thin film of pure water ice under electron beam irradiation on the time-scale of a laboratory experiment. Considering these experimental results, we argue that the phase transition to ice XI readily occurs under high-energy beam irradiation, and could occur in outer space, contrary to the prevailing notion. (c) 2012 Elsevier B.V. All rights reserved.