Pasadena Scientists Map the Milky Way’s Frozen Water Supply With JPL Space Telescope

The water that fills Earth’s oceans may have begun as frost on particles of dust smaller than candle smoke, locked inside enormous frozen clouds drifting between the stars.

That is the picture emerging from a study published Wednesday in The Astrophysical Journal by scientists using the JPL-managed SPHEREx space telescope. The Pasadena-built and operated mission has mapped vast complexes of interstellar ice stretching more than 600 light-years across the Milky Way — frozen reservoirs of water, carbon dioxide, and carbon monoxide that researchers believe are where most of the universe’s water is formed and stored. The mission’s instrument scientist and its principal investigator are both based at Caltech, and its data is processed and archived at IPAC, also at Caltech in Pasadena.

“These vast frozen complexes are like ‘interstellar glaciers’ that could deliver a massive water supply to new solar systems that will be born in the region,” said Phil Korngut, the instrument scientist for SPHEREx at Caltech in Pasadena. “It’s a profound idea that we are looking at a map of material that could rain on nascent planets and potentially support future life.”

The frozen molecules were found inside giant molecular clouds — sprawling regions of gas and dust where dense clumps of matter collapse under gravity, giving birth to stars — in the Cygnus X and North American Nebula regions of the Milky Way. When a new solar system forms near one of these icy clouds, it can inherit the frozen water, according to the NASA press release announcing the findings.

SPHEREx — short for Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer — is the first infrared space mission specifically designed to detect icy molecules across the entire sky, according to NASA. Previous space telescopes, including the James Webb Space Telescope and the retired Spitzer observatory, have detected such molecules in targeted observations, but SPHEREx’s large-scale spectral survey provides something new: a panoramic view of where the ices are concentrated.

“We expected to detect these ices in front of individual bright stars: The light from a star acts like a spotlight, revealing any ice in the space between us and that star. But this is something different,” said lead author Joseph Hora, an astronomer at the Center for Astrophysics at Harvard & Smithsonian. The diffuse background light of the galactic plane, Hora said, shines through entire dust clouds, and SPHEREx can map the distribution of ices within them in detail that was not previously possible.

The study supports a hypothesis that interstellar ice forms on the surface of tiny dust particles, which are no larger than particles found in candle smoke. Dense regions of dust shield the ices from the intense ultraviolet radiation emitted by nearby newborn stars, according to the study. Not all ices behave the same way: water and carbon dioxide respond differently to environmental factors such as ultraviolet light and heating from young stars, and SPHEREx can distinguish between them — something ground-based observatories cannot do, according to study coauthor Gary Melnick, an astronomer at the Center for Astrophysics.

“The SPHEREx mission’s ‘big picture’ view provides valuable new information you can’t get when zooming in on a small region,” Melnick said.

The observatory launched on March 11, 2025, from Vandenberg Space Force Base aboard a SpaceX Falcon 9 rocket. By late 2025, it had completed the first of four planned all-sky infrared maps, charting hundreds of millions of galaxies in three dimensions. The mission is managed by JPL, and its principal investigator is Jamie Bock, a Caltech physicist with a joint JPL appointment. JPL Project Scientist Olivier Doré also oversees the effort. The science analysis is conducted by a team at 13 institutions across the United States, South Korea, and Taiwan, and the SPHEREx dataset is freely available to scientists and the public.

The telescope sees the sky in 102 infrared colors, each representing a different wavelength that offers distinctive information about galaxies, stars, and the regions where planets form. One of the mission’s core goals from the outset has been mapping the chemical signatures of interstellar ice — the frozen molecules that are considered vital to the chemistry that allows life to develop.

The ice maps published Wednesday are among the first scientific results from SPHEREx, and researchers say they represent the beginning, not the conclusion, of the mission’s work on interstellar chemistry. SPHEREx will continue surveying the sky for the remainder of its two-year primary mission, building increasingly detailed maps that scientists hope will illuminate how molecules essential for life reach newly forming planets.

Somewhere in those frozen filaments, threaded through the dark lanes of the Milky Way, is the raw material for oceans that do not yet exist — on worlds that have not yet formed.