NASA’s SPHEREx Reveals Chemically Rich Atmospheres on Free-Floating Brown Dwarfs

NASA’s SPHEREx space telescope is helping astronomers understand brown dwarfs—dark, wandering objects that blur the line between stars and giant exoplanets. A new study published in The Astrophysical Journal shows that these cloudy worlds have chemically rich atmospheres similar to those of Jupiter and Saturn.

What Are Brown Dwarfs?

Brown dwarfs were first discovered in the 1990s. They form when clouds of gas collapse, much like stars, but they do not have enough mass to sustain hydrogen fusion in their cores. These dimly glowing spheres of warm gas share characteristics with Jupiter and Saturn.

Unlike most planets, however, brown dwarfs do not orbit a host star. They drift through space independently and are heated entirely from within.

“They’re kind of goths,” said Zafar Rustamkurov, lead author of the new study and a scientist at IPAC, the California Institute of Technology’s science and data center in Pasadena, California. “Unlike an exoplanet, a free-floating brown dwarf is a completely independent celestial body, disappearing forever on its own. We are still learning how complex they are.”

SPHEREx Detects Water, Methane and Other Molecules

Only a few dozen brown dwarfs have been studied in detail with space telescopes. Astronomers want to observe more of these “dark wanderers” because much of what scientists know about their composition, storms and evolution comes from theoretical models.

NASA’s SPHEREx—short for Spectrophotometer for the History, Reionization Era, and Ice Exploration of the Universe—is an infrared space telescope launched in March 2025 and managed by NASA’s Jet Propulsion Laboratory in Southern California.

The study authors analyzed SPHEREx observations of 37 nearby brown dwarfs spanning a broad temperature range, from about 4,000 degrees Fahrenheit to minus 10 degrees Celsius. SPHEREx measures brightness in 102 different colors, ranging from the deepest red visible to human eyes to the invisible heat of infrared light. This creates a detailed spectrum for each object.

Using these spectra, the researchers identified chemically rich atmospheres containing water, carbon dioxide, carbon monoxide and methane.

“We’re looking at the characteristics of these molecules and how they change from object to object across a temperature range,” said study co-author J. Davey Kirkpatrick, a scientist at Caltech IPAC. “Our paper focused on just 30, but thousands more are being analyzed. We really want to know what boundaries the universe sets on different brown dwarfs.”

“From orbit, SPHEREx will observe wavelengths of light that are basically invisible to ground-based telescopes because the water in Earth’s atmosphere absorbs the light,” Rustamkurov said. “We’re capturing light from a deep red cloud of brown dwarfs that stretches across the sky.”

Brown Dwarfs Offer a New Test for Atmospheric Models

Studying brown dwarfs is a side project for SPHEREx, whose primary mission includes creating an all-sky map. The space telescope must synthesize approximately 3,600 unique images each day to build its all-sky map.

Mapping the distribution of billions of galaxies can help scientists reconstruct what happened during the first billionth of a second after the Big Bang. As SPHEREx scans the sky, it also searches for the chemical ingredients of life, including interstellar ice that could someday contribute to oceans on distant worlds.

Brown dwarfs have previously been discovered by other observatories, including NASA’s James Webb Space Telescope and the retired Spitzer Space Telescope. However, SPHEREx’s broad spectral range is allowing researchers to study thousands of these objects across deep-red and infrared wavelengths.

At these wavelengths, molecules leave distinctive absorption patterns in the light detected from space. As a brown dwarf ages and cools, those patterns change. Some of the brown dwarfs observed by SPHEREx are entering a dynamic stage in which exotic clouds thin and give way to methane-rich atmospheres.

“State-of-the-art models capture general chemical trends, but when it comes to these opaque transitions, the models have a hard time matching the data,” Rustamkurov said. “No two brown dwarfs are the same. Even at the same temperature, their spectra look completely different.”

“This discovery is a call to action to further explore these dark worlds,” Kirkpatrick said. “This journey has turned many of us into accidental meteorologists. We know how difficult it is to predict the weather on our own planet, but we understand that it is just as difficult to explain the phenomena we see on these strange, cold celestial bodies.”

SPHEREx Data Is Available to the Public

The mission is managed by JPL, NASA’s Astrophysics Division within the Science Mission Directorate in Washington. BAE Systems manufactured the telescope and spacecraft bus.

Scientific analysis of SPHEREx data is being conducted by scientists from 13 institutions across the United States, South Korea and Taiwan. The team is led by principal investigator Jamie Bock, who is based at the California Institute of Technology through a joint appointment with JPL, and JPL project scientist Olivier Dore.

Data will be processed and archived at IPAC at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. The SPHEREx dataset is freely available to scientists and the general public.

Media contact
Carla Cofield
Jet Propulsion Laboratory, Pasadena, California
626-808-2469
[email protected]

Written by Sally Younger

2026-069