In a cosmic first, astronomers have pinpointed traces of phosphine, a molecule strongly linked to biological processes on our own planet, in the distant atmosphere of a brown dwarf. Located dozens of light-years away, this celestial body — an object too large to be a planet but too small to ignite as a star — presents an environment utterly inhospitable to life as we understand it.
While this finding does not signal the presence of alien organisms, scientists believe it’s a crucial development in the ongoing quest to locate both phosphine and potential life beyond Earth. By studying how phosphine forms and persists in the extreme conditions of a brown dwarf, researchers can gain vital insights into its chemistry. This knowledge is essential for distinguishing biological sources from non-biological ones and, ultimately, for determining if phosphine could truly be a reliable biomarker for rocky exoplanets.
“We absolutely must thoroughly investigate all the natural pathways this molecule can take to form before we can eliminate them and confidently declare a biological origin,” emphasized Adam Burgasser, an astrophysicist at the University of San Diego and the lead author of the study.
Essentially, understanding phosphine’s fundamental chemistry is paramount before attributing its presence to life.
Phosphine, composed of three hydrogen atoms and one phosphorus atom, is notoriously difficult to create and easily destroyed. On Earth, it’s predominantly a byproduct of microbial life found in harsh environments like decaying swamp vegetation and animal digestive systems. The controversial announcement of phosphine on Venus in 2020 sparked intense interest in the molecule as a potential indicator of life on other worlds.
However, phosphine also occurs naturally in lifeless environments, such as the gas giants Jupiter and Saturn. Therefore, astronomers initially expected to find significant amounts of phosphine in similar exoplanets and brown dwarfs with comparable atmospheres.
Despite years of dedicated observations using the powerful James Webb Space Telescope, these expectations largely went unmet. Phosphine remained elusive or present in negligible quantities, puzzling scientists. The brown dwarf, designated Wolf 1130C, is the first to defy this trend, aligning with earlier predictions.
Dr. Burgasser’s team utilized two instruments on the Webb telescope to analyze the light emitted and absorbed by Wolf 1130C, revealing the chemical composition of its atmosphere. Their analysis uncovered phosphine at a concentration of 100 parts per billion, meaning 100 out of every billion atmospheric particles were phosphine molecules.
“I was initially stunned that we finally detected it,” remarked Eileen Gonzales, an astrophysicist at San Francisco State University, who spearheaded the data analysis. “We’ve been searching for so long.”
Melanie Rowland, an astronomer at the American Museum of Natural History, who was not involved in this particular research but had previously detected much lower concentrations of phosphine on another brown dwarf, noted that the observed abundance on Wolf 1130C matches scientific predictions. However, she found the discovery both thrilling and perplexing, given that Wolf 1130C is an unusual brown dwarf—exceptionally old and largely devoid of heavier elements like oxygen in its atmosphere.
These unique characteristics, Dr. Rowland explained, make it “even more astonishing” that the phosphine levels perfectly align with theoretical models.
The mystery of why other brown dwarfs seem to lack phosphine persists. It’s possible that other, more abundant molecules are obscuring its signal, or that phosphorus is condensing and effectively ‘raining out’ of the atmosphere. Alternatively, current atmospheric models for phosphine abundance might be inaccurate, and Wolf 1130C could simply be a rare exception.
“We simply don’t have a sufficient understanding of its chemistry yet,” Dr. Burgasser concluded.
Phosphine’s scarcity in the universe is a key factor in its appeal as a potential biomarker. It breaks down rapidly when exposed to ultraviolet light and struggles to form in many environments. Yet, this very finicky nature is precisely what makes it a compelling candidate for signaling life, according to Clara Sousa-Silva, an astrochemist at Bard College. Dr. Sousa-Silva was part of both the team that previously suggested phosphine on Venus and the group behind this new brown dwarf discovery.
Discovering phosphine in places incapable of supporting life, Dr. Sousa-Silva believes, “will be a crucial piece of the larger puzzle, helping us decipher phosphine’s role anywhere else, especially in potentially habitable environments.”