NASA's SPHEREx telescope is revealing chemical differences among brown dwarfs, objects that form like stars but cannot sustain the hydrogen fusion of ordinary stars. An October 8 report describes a study of 37 nearby examples across a broad temperature range.
The telescope measures brightness in many wavelength bands, producing a spectrum for each object. Molecules absorb particular parts of the light. Researchers use those patterns to identify atmospheric ingredients, rather than treating the colour of a photograph as a complete chemical analysis.
The study identified signatures associated with water, carbon dioxide, carbon monoxide and methane. Finding these molecules does not establish oceans, life or a solid surface. The observations concern the chemistry of warm, gaseous objects and how their atmospheres differ.
Temperature helps organise the comparison, but it does not explain everything. Some brown dwarfs with similar temperatures have different spectra. NASA says existing models reproduce broad chemical trends more successfully than the complicated transitions associated with changing clouds.
SPHEREx observes wavelengths that Earth's atmosphere makes difficult to study from the ground. Its broad survey also offers a route to a much larger sample. The published analysis covers 37 objects; the thousands being investigated are not all finished results.
The next task is to test atmospheric models against more observations and explain the differences between objects. Brown dwarfs offer a useful laboratory for studying clouds and chemistry beyond the solar system, while showing why a single temperature cannot describe an entire world.