Webb Detects Biosignature Gas Phosphine in Atmosphere of Ancient Brown Dwarf

Astronomers using the NASA / ESA / CSA James Webb space telescope detected phosphine (pH₃) In the atmosphere of Wolf 1130c, a brown dwarf poor in metal in the triple Wolf 1130Abc system.

Diagram of the triple Wolf 1130ABC system, composed of the Red Nwarf Star Wolf 1130a (left), his nearby white dwarf companion and compact Wolf 1130B (in the center), and the Distant Dwarf Brown Brown 1130c (right); The three components of this system are represented at the scale of their relative sizes. Image credit: Adam Burgasser.

Wolf 1130ABC is located about 54 light years in the Cygnus constellation.

Also known LHS 482, Gliese 781 and Ross 1069B, this system consists of three components: the cool Red Star Wolf 1130a, the White Dwarf Wolf 1130B solid and the Brown Dwarf Wolf 1130c.

Discovered for the first time in 2013, Wolf 1130c follows a large orbit around the tight double system of Wolf 1130A and Wolf 1130B.

“Our astronomy program, called Arcana of the Ancients, focuses on old brown dwarfs and poor in metals as a means of testing our understanding of atmospheric chemistry,” said San Diego professor at the University of California, Adam Burgasser.

“Understanding the problem with phosphine was one of our first objectives.”

In atmospheres rich in hydrogen of giant gas planets like Jupiter and Saturn, phosphine is formed naturally.

As such, scientists have long predicted that phosphine should be present in the atmospheres of gas giants in orbit around other stars and in their more massive cousins, brown dwarfs.

However, phosphine has largely escaped detection, even in the previous observations of webb, suggesting problems with our understanding of phosphorus chemistry.

“Before webb, phosphine had to be abundant in the dwarf atmospheres of exoplanet and brunettes, following the theoretical predictions based on the turbulent mixture that we know exists in these sources,” said Dr. Sam Beiler, a postdoctoral researcher at the Trinity College Dublin.

Wolf 1130C was a favorite source for brown dwarf astronomers because of its low abundance of “metals” – essentially all elements other than hydrogen and helium – compared to the sun.

Unlike other brown dwarfs, the authors have identified phosphine in Wolf 1130c’s webb infrared spectral data.

To fully understand the implications of their results, they had to quantify the abundance of this gas in the atmosphere of Wolf 1130c.

“To determine the abundance of molecules in Wolf 1130c, I used a modeling technique known as atmospheric recovery,” said Dr. Eileen Gonzales of the State University of San Francisco.

“This technique uses webb data to support the share of each species of molecular gas in the atmosphere.”

“It’s like the opposite engineering of a really delicious cookie when the chef does not abandon the recipe.”

“It may be that under normal conditions, phosphorus is linked to another molecule such as phosphorus trioxide,” said Dr. Beiler.

“In the depleted atmosphere in metal Wolf 1130c, there is not enough oxygen to take phosphorus, allowing phosphine to form from abundant hydrogen.”

Another possibility is that phosphorus has been generated locally in the Wolf 1130ABC system, in particular by the white dwarf Wolf 1130B.

“A white dwarf is the remaining ball of a star that has finished fusion of his hydrogen,” said Professor Burgasser.

“They are so dense that when they accreat equipment to their surface, they can undergo nuclear reactions on the run, which we detect like Novae.”

While astronomers have not seen such events in the Wolf 1130ABC system in recent history, Novae generally has thousands of thousands of years bursts.

This system has been known for a little over a century, and invisible explosions could have left a heritage in phosphorus pollution.

Understanding why this brown dwarf shows a clear signature of phosphine can lead to new perspectives on the synthesis of the phosphorus of the Milky Way and its chemistry in planetary atmospheres.

“Understanding the chemistry of phosphine in the atmospheres of brown dwarfs where we do not expect that life is crucial if we hope to use this molecule in the search for life on terrestrial worlds beyond our solar system,” said Professor Burgasser.

The study appears today in the journal Science.

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Adam J. Burgasser and al. Observation of phosphine not approved in the atmosphere of a brown dwarf at low temperature. Sciencepublished online on October 2, 2025; Doi: 10.1126 / Science.adu0401