Universe Today
New missions mean new capabilities - and one particularly interesting new mission is finally up and running. Data is starting to come in from SPHEREx, the medium-class surveyor that is mapping the entire sky every six months. A paper based on some of that early data was recently published in The Astrophysical Journal, mapping ice and compounds called Polycyclic Aromatic Hydrocarbons (PAHs) throughout some interesting regions of our Milky Way.
One of those regions is the Cygnus-X star-forming region. It's located about 4,500 light years away from Earth, and is home to more than 3 million solar masses of material. It also hosts the Cygnus OB2 association, a massive cluster of thousands of young stars, including some highly luminous O-type stars that played a critical role in the recent study.
The other region was the North American Nebula - specifically LDN 935, the “dark” region that forms the shape of the “Gulf of Mexico” in that famously shaped nebula that lies 2,600 light years away from Earth. Again, the nebula itself is being constantly shaped by stellar radiation, including being violently ionized by a local O-type star. LDN 935 itself acts as a “cosmic freezer” - its dense clouds insulate its interior from the ultraviolet radiation pumping into its local stellar neighborhood.
Video describing the Cygnus-X star factory. Credit - NASA Video YouTube ChannelThat made the area very well suited for protecting ice. In fact, water and carbon dioxide ice both were found in abundance in LDN 935 and Cygnus-X, mainly distributed along complex, filamentary structures that can extend several degrees across the sky. Ices like this are key building blocks of water planets, such as Earth, and tracking their path through star-forming regions like Cygnus-X is a major step forward in our understanding of that planetary formation process.
PAHs are another key component in those planets, but the researchers found a distinct lack of spatial correlation. In other words, the two types of materials (ices and PAHs) don't like to hang out in the same locations - or at least we can't see them when they do. And that is thanks to ultraviolet radiation. PAHs require UV photons to heat up and emit their spectral signatures - which is how we can see them. Ices, on the other hand, sublimate and get blown away when subjected to that same ultraviolet radiation. So it'd be more accurate to say ice likely won't exist where we can see PAHs. And PAHs are invisible where we can find ice.
Finding all of this material is the job of SPHEREx’s wide field infrared imaging system. It can capture 102 distinct infrared colors (or wavelengths), including some critical ones like 3.05 µm for water ice, 4.27 µm for dry ice, and 3.28 µm for PAHs.
Video from JPL about NASA’s SPHEREx missions. Credit - Jet Propulsion Laboratory YouTube ChannelBut those weren’t the only signatures SPHEREx found in this early dataset. By tracing “hydrogen recombination lines” like the Brackett-alpha line at 4.05 um, the researchers were able to piece together hydrogen shocks emitted by massive protostars like DR 21. While this has been done before, doing so with a wide field survey is certainly novel.
And SPHEREx itself is just getting started. No other telescope in the sky can map the chemical signatures of both ices and organics across multiple degrees in the sky at the same time in a single dataset. It was just launched last year, and some of the data used in this paper was even collected in April 2025, before its regular science operations officially began. Over its two year primary mission plan it should be able to map the entire sky up to four times, allowing scientists to not only pinpoint particularly interesting features, but also watch as they change over time. Keep an eye out for plenty more insights from SPHEREx coming in the near future.
Learn More:
NASA JPL - ‘Interstellar Glaciers’: NASA’s SPHEREx Maps Vast Galactic Ice Regions
J.L. Hora et al - SPHEREx Widefield Infrared Spectral Mapping of Interstellar Ices and Polycyclic Aromatic Hydrocarbons
UT - NASA’s SPHEREx Observatory Completes Its First Map of the Cosmos in 102 Infrared Wavelengths
