Bengaluru: A group of astronomers from the UK, the US and Japan has announced a tantalising new finding about a potential sign of life on Earth’s neighbour Venus, but alien-watchers ought to hold their horses yet.
The researchers behind the finding say it is centred on the detection of the gas phosphine (PH3) in the Venusian atmosphere.
Phosphine is synthesised on Earth by anaerobic lifeforms (those that exist without oxygen) and decaying organic matter. It can also be produced in the laboratory and is highly flammable, as Breaking Bad’s Walter White demonstrated in the series’ pilot episode.
The detection was made using the Atacama (ALMA) array in Chile and the James Clerk Maxwell telescope in Hawaii, and the study involves researchers from the University of Manchester, the Massachusetts Institute of Technology, Cardiff University, the University of Cambridge, Imperial College London, and Kyoto Sangyo University, among others.
The study, led by Jane S. Greaves of Cardiff University, was published in Nature Astronomy Monday evening.
The scientists have made it clear that although their finding offers life as an argument to explain the presence of the gas, it is not evidence of life.
“What we have found is a possible sign of life, but it is not certain that the phosphine is produced by life,” study co-author David L. Clements, a physicist at Imperial College London, told ThePrint. “There may be unusual chemical pathways for its production that we have not found despite examining many thousands of reactions that could produce it,” Clements said.
While the scientists behind the study claim “they have a very high degree of confidence” about the finding, the questions surrounding it primarily centre on the fact that the detection may not be rock solid.
According to a report in the National Geographic, other scientists have said the phosphine detected may be a “false signal”, and may need confirmation before further inferences can be drawn.
Findings and implications
Scientists have studied planetary atmospheres for decades, including those of exoplanets. Studying rocky planets’ atmospheres provides valuable insights into how the gases react with surfaces and sub-surfaces. Emissions, for example, could indicate life or water vapour, which is why scientists keep an avid watch on methane spikes in the Martian atmosphere.
Just like methane, the presence of phosphine can be interpreted as a biosignature, or an indicator of past/present life.
Phosphine is produced on Earth by human activity or by microbes, both of which are capable of maintaining a certain concentration of the gas in the oxygen-filled atmosphere.
But such gases can also be produced by other mechanisms.
It is found in the atmospheres of giant gaseous planets like Jupiter and Saturn because these environments lack oxygen and are at high temperatures and pressures, causing the same chemical reactions as in labs. But rocky planets do not have environments conducive to the natural production of phosphine, making it a potentially good indicator for life.
In 2017, the research team behind the phosphine detection had set about performing a theoretical experiment to determine how much of the gas would need to be detected to indicate life on Venus.
To their enormous surprise, they detected much more of the gas than they expected, about 20 parts per billion. The number was impossibly high for an environment that contained oxygen, and nearly a thousand times more than is found on Earth. After bending numbers to find an explanation in their readings, the team looked at natural causes.
First, they eliminated accidental observations of other gases, such as ammonia, which can falsely reflect as phosphine. Then, they examined the composition of the atmosphere and the reactions that could produce phosphine, only to conclude that the conditions are simply not good enough to produce the gas at such high concentrations.
Additionally, they also ended up eliminating planetary phenomena like volcanism or lightning for not being powerful enough. Other “exotic processes” such as large-scale friction or the solar wind also produce the gas only in negligible amounts, they said.
Furthermore, in the conditions where phosphine was found, the gas should survive for just about three years, the researchers said. But the presence of the gas there today indicates that there is an active process that is producing it, they added.
Life in the clouds
For many decades, it has been theorised that the higher, cooler parts of Venus’ thick atmosphere could potentially host microbial life.
Venus is the hottest planet in the solar system — even though Mercury is closer to the Sun — with an average surface temperature of 450°C. This is because of its dense atmosphere — the thickest of the four rocky planets — is 96 per cent carbon dioxide.
Scientists theorise that the planet was much cooler in the past, but a runaway greenhouse effect caused temperatures to soar — a fate scientists think awaits Earth if humanity does not act soon against climate change.
Research so far suggests that, about 50km above the surface, at the top of the clouds, the environment of Venus is more temperate. Since at least the 1960s, some scientists have considered the possibility that pockets of Venus’ upper clouds may host microbial life, despite the extremely acidic conditions.
The planet’s soaring temperatures make it hard for spacecraft to land on the surface, and function for long. The longest surviving lander was the Soviet mission Venera 12, which sent back data for 110 minutes in 1978.
Currently, only Japan’s Akatsuki probe is in orbit around Venus, although more missions are planned. Both Russia and India are planning to send missions to the planet to study the atmosphere. Neither mission is approved yet.
India’s proposed project, Shukrayaan-1, is said to be slated for 2023. The orbiter will carry a balloon probe that, according to plans, will settle at a height of 55 km above the Venusian surface, around where phosphine has been detected.
Talking about the road ahead, Clements said, “A life-finding mission that could fly into the clouds would be ideal, and a sample-return mission would allow the full power of an earthly biochemistry lab to investigate what we have found, but devising and building such missions will take some time.”
At the moment, the researchers are still working on obtaining more data using the same telescopes, as well as observing how phosphine concentrations change over time. They’re also hoping to tap into any future missions that fly by to perform more detailed observations, and to ultimately conclude if they have indeed found the first evidence of life outside Earth.
“If it is life, then the implications are profound,” said Clements. “We will have found life on another planet, something that philosophers, astronomers, and astrobiologists have been looking for and speculating about for many many years.”
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