Scientists have detected an unstable and unexpected gas in the atmosphere of Venus that, on Earth, is commonly produced by some microbes.
The finding could be a sign of life in the clouds of our closest planetary neighbor, or it could simply be evidence of some strange and still unknown chemical processes that take place there. Science
The gas “is present at much higher levels than can be explained by known production methods,” says Lewis Dartnell, an astrobiologist at the University of Westminster who was not involved in the new study.
The researchers detected a distinctive gas signature, phosphine, in Venus’ atmosphere in June 2017 using a ground-based telescope. The observation was later confirmed in March 2019 with another telescope of this type.
The instruments showed a slight reduction in light at a wavelength only known to be absorbed by gas, report Jane Greaves, an astronomer at Cardiff University, and her colleagues in Nature Astronomy.
Absorption levels suggest that phosphine is present in concentrations of up to 20 parts per billion at altitudes above 33 miles, Greaves says.
Although 20 parts per billion sounds like a negligible amount, there shouldn’t even be that much. Phosphine is relatively unstable and in the harsh superacidic conditions found high in the Venusian atmosphere, the half-life of a molecule is about 16 minutes. To counter the ongoing destruction of the gas, there must be a constant and prodigious source.
Greaves and his team tried to figure out where all that phosphine comes from. Minerals containing phosphorus, a possible crude ingredient in phosphine, are unlikely to rise high from the planet’s surface. Chemical reactions caused by rays and sunlight would not produce enough gas either. Volcanoes on Earth spew very small amounts of phosphine, but it would take about 200 times more volcanic activity on Venus to explain the levels seen there.
On Earth, a variety of microbes that thrive in low-oxygen environments produce phosphine. And those organisms would only need to pump out 10% of the phosphine they make here to explain the levels seen on Venus, the team notes. At altitudes between 53 and 61 kilometers above the surface of Venus, temperatures are a mild 30 ° C. That is certainly more microbe friendly than the hellish melting temperatures of lead of about 900 ° C at ground level. However, life as we know it would struggle in the hyperacidic and dehydrating conditions of Venus’s atmosphere, regardless of temperature.
The presence of phosphine is not a sure sign of life, says study co-author Sukrit Ranjan, a planetary scientist at the Massachusetts Institute of Technology. The chemistry of phosphine is not well understood, and it is possible that the gas could more easily persist in the lower temperate layers of the Venusian atmosphere, which could be shielded from sunlight that drives photochemical reactions that destroy phosphine.
The team’s observations are “curious and inexplicable,” says Dartnell. Even if the tiny Venusians aren’t responsible for phosphine, he notes, “at least they’ve discovered an interesting new atmospheric chemistry.”