‘Interstellar Glaciers’: NASA’s SPHEREx Maps Vast Galactic Ice Regions

NASA’s SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission has mapped interstellar ice on an unprecedented scale. Covering regions of our Milky Way galaxy with a diameter of more than 600 light years, the ice has been found inside giant molecular clouds – vast regions of gas and dust where dense clumps of matter collapse under gravity, giving rise to stars. A study describing these results published Wednesday in The Astrophysical Journal.

One of the main goals of SPHEREx is to map the chemical signatures of different types of interstellar ice. This ice includes molecules like water, carbon dioxide, and carbon monoxide, which are essential to the chemistry that allows life to develop. Researchers believe that these reservoirs of ice, attached to the surface of tiny dust grains, are where most of the universe’s water is formed and stored. The water in Earth’s oceans – as well as the ices of comets and other planets and moons in our galaxy – come from these regions.

“These vast frozen complexes are like ‘interstellar glaciers’ that could provide a massive supply of water to new solar systems being born in the region,” said Phil Korngut, study co-author and SPHEREx instrument scientist at Caltech in Pasadena, California. “It’s a profound idea that we’re looking at a map of materials that could rain down on nascent planets and potentially harbor future life.”

Thanks to its spectral capabilities, SPHEREx can measure the quantities of different ices and molecules, such as polycyclic aromatic hydrocarbons, in and around molecular clouds, helping scientists better understand their composition and environment.

Although space telescopes such as NASA’s James Webb Space Telescope and the agency’s retired Spitzer have detected water, carbon dioxide, carbon monoxide, and other icy molecules throughout our galaxy, the SPHEREx observatory is the first infrared mission specifically designed to find such molecules throughout the sky via the mission’s large-scale spectral survey.

“We expected to detect these ices in front of individual bright stars: the light from a star acts like a searchlight, 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 Harvard & Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts. “When we look along the galactic plane – where most of our galaxy’s stars, gas and dust are concentrated – there is a lot of diffuse background light shining through entire dust clouds, and SPHEREx can see the spatial distribution of the ices within them in incredible detail.”

Operated by NASA’s Jet Propulsion Laboratory in Southern California, the SPHEREx observatory was launched on March 11, 2025 and has the unique ability to view the sky in 102 colors, each representing a different wavelength of infrared light that offers distinctive information about galaxies, stars, planet-forming regions and other cosmic features. By the end of 2025, SPHEREx had produced the first of four all-sky infrared maps of the universe, plotting the positions of hundreds of millions of galaxies in 3D to help answer major questions about the cosmos, including those about the origins of water and life.

Using SPHEREx maps of various icy molecules, the study authors were able to take an in-depth look at many molecular clouds in the Cygnus X and North American Nebula regions of the Milky Way. In the densest areas, where the amount of dust is greatest, dark filamentous bands block visible light from stars behind them. Using its infrared eye, the space telescope also revealed where different ices – which absorb specific wavelengths of infrared light that would pass through clouds if they were just dust – are densest.

This finding supports the hypothesis that interstellar ice forms on the surface of tiny dust particles, which are no larger than particles found in candle smoke, and that dense regions of dust protect the ices from intense ultraviolet radiation emitted by newborn stars. However, not all ice is treated the same in the interstellar medium.

“We can study the environmental factors that contribute to different rates of ice formation across large areas of interstellar space,” said Gary Melnick, co-author of the study and also an astronomer at CfA. “The overview of the SPHEREx mission provides valuable new information that you cannot get by zooming in on a small region. »

From this broad perspective, Melnick adds, SPHEREx can do something that ground-based observatories cannot: detect varying amounts of water and carbon dioxide, two ices that respond differently to environmental factors. For example, the presence of intense ultraviolet light from nearby young massive stars or the heating of these dust grains by this light affects the abundance of different ices in different ways.

This is only the beginning of the mission. SPHEREx observations will provide scientists with a powerful tool to explore the different components of our galaxy, the physics of the interstellar medium that leads to the formation of stars and planets, and the chemical processes that transport molecules essential for life to newly formed planets.

The mission is managed by JPL for the agency’s Astrophysics Division within the Science Mission Directorate in Washington. The telescope and space bus were built by BAE Systems in Boulder, Colorado. The scientific analysis of the SPHEREx data is being conducted by a team of scientists from 13 institutions in the United States, South Korea, and Taiwan, led by principal investigator Jamie Bock, based at Caltech with a joint appointment at JPL, and Olivier Doré, JPL project scientist. The data is processed and archived at Caltech’s IPAC in Pasadena, which manages JPL for NASA. The SPHEREx dataset is freely available to scientists and the public.

For more information on the SPHEREx mission, visit:

https://science.nasa.gov/mission/spherex/

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Jet Propulsion Laboratory, Pasadena, California.
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Amy C. Oliver, FRAS
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Smithsonian Astrophysical Observatory
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2026-022