NASA's SPHEREx spacecraft reveals complex atmospheric chemistry in free-floating brown dwarfs
New spectroscopic observations of 37 nearby brown dwarfs show chemically rich atmospheres and significant variation that current models struggle to explain.
What happened
NASA's SPHEREx spacecraft observed 37 nearby brown dwarfs across 102 wavelengths of light, from visible red to infrared, revealing detailed atmospheric composition. The study, published September 28 in The Astrophysical Journal, determined that brown dwarf atmospheres are rich in water, carbon dioxide, carbon monoxide, and methane. Researchers found that some brown dwarfs are undergoing extreme atmospheric changes as they age, with clouds clearing to create methane-rich atmospheres. The observations showed significant chemical variation among brown dwarfs: even objects at the same temperature display distinct spectra, with no two brown dwarfs alike.
Context
Brown dwarfs are substellar objects with masses between 13 and 80 times that of Jupiter—they form like stars from collapsing gas clouds but lack sufficient mass to trigger hydrogen fusion in their cores. Since their discovery in the 1990s, they have remained poorly understood because their minimal nuclear fusion produces only faint glow, leaving knowledge of their makeup, storms, and evolution largely theoretical. SPHEREx's wide wavelength coverage is particularly valuable for studying brown dwarfs because it can detect infrared light that Earth's atmosphere blocks from ground-based telescopes. The research reveals that existing atmospheric models capture general chemical trends but fail to explain the cloudy transitions observed in these objects, indicating fundamental gaps in understanding brown dwarf behavior.