Summary
An analysis of SPHEREx observations of 37 nearby brown dwarfs found atmospheric signatures of water, carbon dioxide, carbon monoxide and methane. The spectra also show differences among objects that current models struggle to explain during cloudy transitions.
NASA reports that an analysis of observations from its SPHEREx space telescope has identified chemically varied atmospheres across 37 nearby brown dwarfs. Published in The Astrophysical Journal, the study found spectral signatures of water, carbon dioxide, carbon monoxide and methane across objects spanning a wide range of temperatures.
Brown dwarfs form from collapsing clouds of gas, as stars do, but lack enough mass to sustain hydrogen fusion in their cores. They share some characteristics with giant planets such as Jupiter and Saturn. Studying their atmospheres can help researchers test how these objects change as they cool.
How SPHEREx reads their light
SPHEREx observes the sky in infrared and visible wavelengths. For this study, it measured each brown dwarf’s brightness in 102 different colours, building a spectrum: a record of how much light reaches the telescope at different wavelengths. Molecules absorb particular wavelengths, leaving patterns in a spectrum that can reveal which substances are present.
The 37 objects in the study span temperatures from about 4,000°F (2,200°C) to −10°F (−20°C). SPHEREx’s view from space includes wavelengths that are difficult to observe from the ground because water in Earth’s atmosphere absorbs them.
Brown dwarfs have been observed by other telescopes, including NASA’s James Webb Space Telescope and the retired Spitzer Space Telescope. SPHEREx’s broad spectral coverage is helping researchers examine thousands of these objects; the study reported here focuses on three dozen.
Atmospheric chemistry varies with temperature
The observed spectra showed signatures of water, carbon dioxide, carbon monoxide and methane. The study’s authors report that the molecular patterns change from one object to another across the temperature range. Some of the brown dwarfs are in a transition as their clouds thin and methane-rich atmospheres become more prominent.
That transition is a challenge for existing models. NASA’s account of the study says the models capture broad chemical trends but struggle to match the observations during cloudy transitions. The contrast between model predictions and the measured spectra gives researchers a way to refine their understanding of brown-dwarf atmospheres and their evolution.
The published analysis covers 37 nearby objects, while the research team is processing observations of thousands more. Examining that larger collection could show how widely the chemical patterns seen in this sample occur. SPHEREx also uses its all-sky survey to support other research, including mapping galaxies and searching for interstellar ice.