Trace gas phosphine points to volcanic activity on Venus

Scientists last autumn revealed that the gas phosphine was found in trace amounts in Venus’ upper atmosphere. That discovery promised the slim possibility that phosphine serves as a biological signature for the hot, toxic planet.

Now Cornell scientists say the phosphine’s chemical fingerprints support a different and important scientific find: evidence of explosive volcanoes on the mysterious planet.

“The phosphine is not telling us about the biology of Venus,” said Jonathan Lunine, the David C. Duncan Professor in Physical Sciences and chair of the Department of Astronomy in the College of Arts and Sciences. “It’s telling us about the geology. Science is pointing to a planet that has active explosive volcanism today or in the very recent past.”

Lunine and Ngoc Truong, a doctoral candidate in geology, have authored the study, “Volcanically Extruded Phosphides as an Abiotic Source of Venusian Phosphine,” published July 12 in the Proceedings of the National Academy of Sciences.

Truong and Lunine argue that volcanism is the means for phosphine to get into Venus’ upper atmosphere, after examining observations from the ground-based, submillimeter-wavelength James Clerk Maxwell Telescope atop Mauna Kea in Hawaii, and the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile.

“Volcanism could supply enough phosphide to produce phosphine,” Truong said. “The chemistry implies that phosphine derives from explosive volcanoes on Venus, not biological sources.”

Our planetary neighbor broils with an almost 900-degree Fahrenheit average surface temperature and features a carbon dioxide-filled atmosphere enveloped in sulfuric acid clouds, according to NASA.

If Venus has phosphide – a form of phosphorous present in the planet’s deep mantle – and, if it is brought to the surface in an explosive, volcanic way and then injected into the atmosphere, those phosphides react with the Venusian atmosphere’s sulfuric acid to form phosphine, Truong said.

He found published laboratory data confirming that the phosphide reacts with sulfuric acid to produce phosphines efficiently.

Volcanism on Venus is not necessarily surprising, Lunine said. But while “our phosphine model suggests explosive volcanism occurring, radar images from the Magellan spacecraft in the 1990s show some geologic features could support this.”

In 1978, on NASA’s Pioneer Venus orbiter mission, scientists uncovered variations of sulfur dioxide in Venus’ upper atmosphere, hinting at the prospect of explosive volcanism, Truong said, similar to the scale of Earth’s Krakatoa volcanic eruption in Indonesia in 1883.

Said Truong: “Confirming explosive volcanism on Venus through the gas phosphine was totally unexpected.”

Funding for the research was provided by the NASA Goddard Space Flight Center in Greenbelt, Maryland.

Read the story in the Cornell Chronicle.

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