The SPHEREx telescope analyzed observations of 37 nearby brown dwarfs, revealing atmospheres rich in water, carbon dioxide, carbon monoxide, and methane. Its coverage of red and infrared wavelengths enables the study of thousands of these objects that have not previously been examined in detail.
NASA’s SPHEREx space telescope has revealed chemical details in the atmospheres of brown dwarfs, objects whose properties lie between those of stars and giant planets. Results published in The Astrophysical Journal showed the presence of water, carbon dioxide, carbon monoxide, and methane in the atmospheres of these objects, with clear differences from one brown dwarf to another.
Brown dwarfs form through the collapse of gas clouds like stars, but they do not have enough mass to sustain hydrogen fusion in their cores. They therefore remain warm, faintly glowing objects that do not necessarily orbit a star or depend on one for heat. They share some characteristics with Jupiter and Saturn, but differ from most planets in being free-floating objects in space.
Spectra Covering a Broad Temperature Range
Researchers analyzed data from 37 nearby brown dwarfs covering a broad range of temperatures, from about 2,200 to minus 20 degrees Celsius. SPHEREx measures the brightness of objects in 102 different colors, beginning with deep visible red and extending into invisible infrared light, producing spectral fingerprints that reveal the molecules present in their atmospheres.
These molecules display distinctive absorption patterns in the light emitted into space. The patterns change as a brown dwarf ages and cools. The team also observed objects passing through a stage in which their thick clouds recede, revealing atmospheres richer in methane.
What Does SPHEREx Add?
Only a limited number of brown dwarfs have been studied in detail using space telescopes. SPHEREx, which launched in March 2025, has spectral coverage that enables it to image thousands of them in deep red and infrared light bands—ranges that are difficult to observe from Earth because the atmosphere absorbs some of their wavelengths.
This work is a secondary mission carried out as part of the telescope’s comprehensive survey of the sky. SPHEREx captures about 3,600 unique images each day to build maps of the sky, alongside its primary objectives related to the distribution of galaxies, the history of the early universe, and the search for the chemical ingredients of life and interstellar ice.
Scientific Benefits and Limitations
The results show that current models successfully represent general chemical trends, but still struggle to match the data during cloud-transition stages. Differences in the spectra of objects with similar temperatures indicate that understanding the weather and chemical evolution of brown dwarfs remains incomplete.
Analyzing the first dozens marks the beginning of a broader program, as scientists work to study thousands of additional objects. SPHEREx data are available free of charge to scientists and the public, expanding the potential research base on the strange atmospheres of objects that resemble giant planets but are not linked to a host star.