Possible sign of life detected in the atmosphere of Venus

This artistic illustration depicts the Venusian surface and atmosphere. Credit: ESO/M. Kornmesser

An international team of astronomers today announced the discovery of a rare molecule — phosphine — in the clouds of Venus. On Earth, this gas is only made industrially or by microbes that thrive in oxygen-free environments. Astronomers have speculated for decades that high clouds on Venus could offer a home for microbes — floating free of the scorching surface but needing to tolerate very high acidity. The detection of phosphine could point to such extra-terrestrial “aerial” life. Confirming the presence of life, however, will require much more work.

“When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”, says team leader Jane Greaves of Cardiff University in the UK, who first spotted signs of phosphine in observations from the James Clerk Maxwell Telescope (JCMT), operated by the East Asian Observatory, in Hawaiʻi. Confirming their discovery required using 45 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, a more sensitive telescope in which the European Southern Observatory (ESO) is a partner. Both facilities observed Venus at a wavelength of about 1 millimeter, much longer than the human eye can see — only telescopes at high altitude can detect it effectively.

The international team, which includes researchers from the UK, US and Japan, estimates that phosphine exists in Venus’s clouds at a small concentration, only about twenty molecules in every billion. Following their observations, they ran calculations to see whether these amounts could come from natural non-biological processes on the planet. Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning, but none of these could make anywhere near enough of it. These non-biological sources were found to make at most one ten thousandth of the amount of phosphine that the telescopes saw.

To create the observed quantity of phosphine (which consists of hydrogen and phosphorus) on Venus, terrestrial organisms would only need to work at about 10% of their maximum productivity, according to the team. Earth bacteria are known to make phosphine: they take up phosphate from minerals or biological material, add hydrogen, and ultimately expel phosphine. Any organisms on Venus will probably be very different to their Earth cousins, but they too could be the source of phosphine in the atmosphere.

While the discovery of phosphine in Venus’s clouds came as a surprise, the researchers are confident in their detection. “To our great relief, the conditions were good at ALMA for follow-up observations while Venus was at a suitable angle to Earth. Processing the data was tricky, though, as ALMA isn’t usually looking for very subtle effects in very bright objects like Venus,” says team member Anita Richards of the UK ALMA Regional Centre and the University of Manchester. “In the end, we found that both observatories had seen the same thing — faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below,” adds Greaves, who led the study published today in Nature Astronomy.

Another team member, Clara Sousa Silva of the Massachusetts Institute of Technology in the US, has investigated phosphine as a “biosignature” gas of non-oxygen-using life on planets around other stars, because normal chemistry makes so little of it. She comments: “Finding phosphine on Venus was an unexpected bonus! The discovery raises many questions, such as how any organisms could survive. On Earth, some microbes can cope with up to about 5% of acid in their environment — but the clouds of Venus are almost entirely made of acid.”

The team believes their discovery is significant because they can rule out many alternative ways to make phosphine, but they acknowledge that confirming the presence of “life” needs a lot more work. Although the high clouds of Venus have temperatures up to a pleasant 30 degrees Celsius, they are incredibly acidic — around 90% sulfuric acid — posing major issues for any microbes trying to survive there.

ESO astronomer and ALMA European Operations Manager Leonardo Testi, who did not participate in the new study, says: “The non-biological production of phosphine on Venus is excluded by our current understanding of phosphine chemistry in rocky planets’ atmospheres. Confirming the existence of life on Venus’s atmosphere would be a major breakthrough for astrobiology; thus, it is essential to follow-up on this exciting result with theoretical and observational studies to exclude the possibility that phosphine on rocky planets may also have a chemical origin different than on Earth.”

More observations of Venus and of rocky planets outside our Solar System, including with ESO’s forthcoming Extremely Large Telescope, may help gather clues on how phosphine can originate on them and contribute to the search for signs of life beyond Earth.

Ancient organic material, mysterious methane on Mars

This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp. Image Credit: NASA/JPL-Caltech/MSSS
This low-angle self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called “Buckskin” on lower Mount Sharp. Image Credit: NASA/JPL-Caltech/MSSS

From a NASA News Release

NASA’s Curiosity rover has found new evidence preserved in rocks on Mars that suggests the planet could have supported ancient life, as well as new evidence in the Martian atmosphere that relates to the search for current life on the Red Planet. While not necessarily evidence of life itself, these findings are a good sign for future missions exploring the planet’s surface and subsurface.

The new findings – “tough” organic molecules in three-billion-year-old sedimentary rocks near the surface, as well as seasonal variations in the levels of methane in the atmosphere – appear in the June 8 edition of the journal Science.

Organic molecules contain carbon and hydrogen, and also may include oxygen, nitrogen and other elements. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life.

“With these new findings, Mars is telling us to stay the course and keep searching for evidence of life,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters, in Washington. “I’m confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet.”

“Curiosity has not determined the source of the organic molecules,” said Jen Eigenbrode of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is lead author of one of the two new Science papers. “Whether it holds a record of ancient life, was food for life, or has existed in the absence of life, organic matter in Martian materials holds chemical clues to planetary conditions and processes.”

Although the surface of Mars is inhospitable today, there is clear evidence that in the distant past, the Martian climate allowed liquid water – an essential ingredient for life as we know it – to pool at the surface. Data from Curiosity reveal that billions of years ago, a water lake inside Gale Crater held all the ingredients necessary for life, including chemical building blocks and energy sources.

“The Martian surface is exposed to radiation from space. Both radiation and harsh chemicals break down organic matter,” said Eigenbrode. “Finding ancient organic molecules in the top five centimeters of rock that was deposited when Mars may have been habitable, bodes well for us to learn the story of organic molecules on Mars with future missions that will drill deeper.”

Seasonal Methane Releases

In the second paper, scientists describe the discovery of seasonal variations in methane in the Martian atmosphere over the course of nearly three Mars years, which is almost six Earth years. This variation was detected by Curiosity’s Sample Analysis at Mars (SAM) instrument suite.

Water-rock chemistry might have generated the methane, but scientists cannot rule out the possibility of biological origins. Methane previously had been detected in Mars’ atmosphere in large, unpredictable plumes. This new result shows that low levels of methane within Gale Crater repeatedly peak in warm, summer months and drop in the winter every year.

“This is the first time we’ve seen something repeatable in the methane story, so it offers us a handle in understanding it,” said Chris Webster of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, lead author of the second paper. “This is all possible because of Curiosity’s longevity. The long duration has allowed us to see the patterns in this seasonal ‘breathing.'”

Finding Organic Molecules

To identify organic material in the Martian soil, Curiosity drilled into sedimentary rocks known as mudstone from four areas in Gale Crater. This mudstone gradually formed billions of years ago from silt that accumulated at the bottom of the ancient lake. The rock samples were analyzed by SAM, which uses an oven to heat the samples (in excess of 900 degrees Fahrenheit, or 500 degrees Celsius) to release organic molecules from the powdered rock.

SAM measured small organic molecules that came off the mudstone sample – fragments of larger organic molecules that don’t vaporize easily. Some of these fragments contain sulfur, which could have helped preserve them in the same way sulfur is used to make car tires more durable, according to Eigenbrode.

The results also indicate organic carbon concentrations on the order of 10 parts per million or more. This is close to the amount observed in Martian meteorites and about 100 times greater than prior detections of organic carbon on Mars’ surface. Some of the molecules identified include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.

In 2013, SAM detected some organic molecules containing chlorine in rocks at the deepest point in the crater. This new discovery builds on the inventory of molecules detected in the ancient lake sediments on Mars and helps explains why they were preserved.

Finding methane in the atmosphere and ancient carbon preserved on the surface gives scientists confidence that NASA’s Mars 2020 rover and ESA’s (European Space Agency’s) ExoMars rover will find even more organics, both on the surface and in the shallow subsurface.

These results also inform scientists’ decisions as they work to find answers to questions concerning the possibility of life on Mars.

“Are there signs of life on Mars?” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program, at NASA Headquarters. “We don’t know, but these results tell us we are on the right track.”

This work was funded by NASA’s Mars Exploration Program for the agency’s Science Mission Directorate (SMD) in Washington. Goddard provided the SAM instrument. JPL built the rover and manages the project for SMD.