The presence of water vapor near the Orion nebula is indicated by an increased flux of infrared radiation at specific wavelengths, which provides a unique fingerprint of water molecules. The strength of the observed radiation tells astrophysicists the concentration of water vapor that is present.

The panels at the upper left and lower right show two examples of flux measurements carried out by the Long Wavelength Spectrometer (LWS) on board the European Space Agency's Infrared Space Observatory (ISO). They indicate the presence of a large concentration of water vapor.

The central panel is an image of the Orion nebula taken with the Wide Field Planetary Camera 2 (WFPC2) on NASA's Hubble Space Telescope (HST) and shows the region of space where the water vapor was detected.