Astrochemistry Update: 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 at an unprecedented scale.

Covering regions in our Milky Way galaxy more than 600 light-years across, the ice was found inside giant molecular clouds — vast regions of gas and dust where dense clumps of matter collapse under gravity, giving birth to stars. A study describing these findings published Wednesday in The Astrophysical Journal.

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

“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 study coauthor Phil Korngut, the instrument scientist for SPHEREx at Caltech in Pasadena, California. “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.”

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

Three selected regions of H₂O ice and CO₂ ice absorption line images from Figure 3, along with the corresponding section of the PAH line image. The ice absorption images show the peak optical depth in the feature in inverse grayscale, ranging from 0 to 1.1. The PAH images show lower-flux regions as black and higher-flux regions as white. The top images zoom in on a region near the center of the CygX mosaic shown in Figure 1 and include DR 15, which is the bright H ii region near the bottom of the PAH image. The middle images include the dark cloud LDN 896. The bottom row shows the dark cloud complex that is slightly to the right of center in Figure 1, cataloged as the Two Micron All Sky Survey dark clouds Dobashi 2362 and 2367 (K. Dobashi 2011) and known from Spitzer/IRAC imaging as being composed of a network of filamentary dark clouds (J. Pari & J. L. Hora 2020). — The Astrophysical Journal

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 over the entire 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 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 (CfA) at Harvard & Smithsonian in Cambridge, Massachusetts.

“When looking along the galactic plane — where most of the stars, gas, and dust of our galaxy are concentrated — there’s a lot of diffuse background light shining through entire dust clouds, and SPHEREx can see the spatial distribution of the ices they contain in incredible detail.”

Managed by NASA’s Jet Propulsion Laboratory in Southern California, the SPHEREx observatory launched March 11, 2025, and has the unique ability to see 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 late 2025, SPHEREx had completed the first of four all-sky infrared maps of the universe, charting 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.

Icy origins

Using the SPHEREx maps of various icy molecules, the study’s authors were able to look deep into 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 filamentary lanes block the visible light from the stars behind. With its infrared eye, the space telescope also revealed where the different ices — which absorb specific wavelengths of infrared light that would pass through the clouds if they consisted only of dust — are at their 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 the dense regions of dust shield the ices from the intense ultraviolet radiation emitted by newborn stars. However, not all ices are treated the same way in the interstellar medium.

“We can investigate the environmental factors that contribute to different ice formation rates across large areas of interstellar space,” said study coauthor Gary Melnick, also an astronomer at the CfA. “The SPHEREx mission’s ‘big picture’ view provides valuable new information you can’t get when zooming in on a small region.”

Within this broad perspective, adds Melnick, SPHEREx can do something 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 massive young stars or the heating of these dust grains by that light affects the abundances of different ices in distinct ways.

This is just the beginning for the mission. Observations from SPHEREx will provide scientists with a powerful tool to explore the various components of our galaxy, the physics of the interstellar medium that lead to star and planet formation, and the chemical processes that deliver molecules essential for life to newly formed planets.

More about SPHEREx

The mission is managed by JPL for the agency’s Astrophysics Division within the Science Mission Directorate in Washington. The telescope and the spacecraft bus were built by BAE Systems in Boulder, Colorado. The science analysis of the SPHEREx data is being conducted by a team of scientists at 13 institutions across the U.S. and in South Korea and Taiwan, led by Principal Investigator Jamie Bock, who is based at Caltech with a joint JPL appointment, and by JPL Project Scientist Olivier Doré. Data is processed and archived at IPAC at Caltech in Pasadena, which manages JPL for NASA. The SPHEREx dataset is freely available to scientists and the public.

For more information about the SPHEREx mission visit: https://science.nasa.gov/mission/spherex/

SPHEREx Widefield Infrared Spectral Mapping of Interstellar Ices and Polycyclic Aromatic Hydrocarbons, The Astrophysical Journal (open access)

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