Brown Dwarf Discovery Could Tell Us More About Venus

The James Webb Space Telescope (JWST) was reported to have discovered phosphine in the atmosphere of a brown dwarf — the same chemical that stoked controversy following claims that it had been detected on Venus and could be coming from life.

This new detection on a brown dwarf is predicted by models that simulate alien atmospheres and is a reminder that phosphine is not necessarily a biosignature. However, astronomers remain puzzled about why some objects contain phosphine and others do not, even though theory says it should be there.

The phosphine was identified in the cold atmosphere of a brown dwarf called Wolf 1130C, which exists in a triple system along with a low-mass red dwarf star and a white dwarf. The phosphine exists with an abundance of 0.1 parts per million, which matches what models of the atmosphere of gas giant planets and brown dwarfs predict. Indeed, both Jupiter and Saturn contain a similar abundance of phosphine to Wolf 1130C.

The problem has been that many brown dwarfs that are expected to show detectable abundances of phosphine do not, and scientists don't know why.

Phosphine is a phosphorus-based molecule, composed of one atom of phosphorus and three hydrogen atoms. It is also pretty unstable in atmospheric conditions, and chemical reactions can easily break phosphine molecules apart. We see phosphine in Jupiter and Saturn's clouds because it is formed deep within the hot interiors of the giant planets, and then convection currents carry the phosphine to higher altitudes faster than the rate at which it is destroyed.

This is one of the reasons why the claimed detection of phosphine on Venus is so controversial.

It was in 2020 that a team led by Jane Greaves of the University of Cardiff in Wales detected phosphine in Venus' atmosphere using the James Clerk Maxwell Telescope in Hawaii and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. On Earth, phosphine occurs naturally as a product of biological processes, and Greaves' team strongly pushed the biological angle to explain their discovery, leading to speculation that there could be microbes living in Venus' toxic clouds.

However, a large section of the astronomical community differed with the team's findings, arguing that there were flaws in the analysis, and other groups have struggled to replicate the findings. In spite of this, Greaves' team has doubled down on their conclusions, and the presence of phosphine on Venus remains fiercely debated and controversial.

Part of scientists' disagreement with the discovery is that they find it hard to see how the phosphine could survive in Venus' atmosphere.

Nevertheless, phosphine is still considered a potential biosignature by astrobiologists in their search for alien life.

However, its existence in the clouds of Jupiter and Saturn, and now on Wolf 1130C, is a reminder that non-biological chemical processes can also produce phosphine. The question is why Jupiter, Saturn and Wolf 1130C have detectable levels of phosphine while other brown dwarfs that have been studied by JWST do not, or at least are so depleted in it that the molecule is not detectable.