In dark gas-and-dust clouds where stars are born, interstellar dust grains are coated with icy crusts. This Water is the main oxygen reservoir for future planets. The SPHEREx telescope peered into several such clouds and built detailed maps of ice distribution. Instead of waiting for rare background stars, astronomers used the clouds' own light — a faint scattered glow akin to mist in distant streetlights. Ice absorbs part of this glow, and the depth of the shadow reveals where there is more.
Why this happens is still unclear. Computer models accounting for light scattering and dust properties could not reproduce this dip. Apparently, in superdense conditions where the temperature is just ten degrees above absolute zero, ice transforms into other substances: for example, frozen carbon monoxide or complex organics. The discovery means that the chemical composition of future planetary systems may differ greatly from what we imagined, and depends on what happened to the ice even before the star was born.
SPHEREx is a true cosmic 'ice cartographer': every six months it builds a complete map of the sky, and its data already contain millions of spectra available for searching for traces of frozen water in the cradles of future planets.
Although the scattered glow of pre-stellar cores does not appear directly in science fiction plots, the idea of 'ice storing history' resonates with the image of a giant ice library in Kim Stanley Robinson's novel '2312' — except here the chemical evolution of the cloud is recorded.