An announcement by an international team of astronomers about the discovery of phosphine gas in the atmosphere of Venus on Monday triggered global excitement about the possibility of the presence of lifeforms on the neighbouring planet. Apart from being produced in industrial processes, phosphine, a colourless but smelly gas, is known to be made only by some species of bacteria that survive in the absence of oxygen.
In a paper published in Nature Astronomy, a team of scientists have reported traces of phosphine in a concentration of approximately 20 parts per billion, thousands to millions of times more than what could otherwise be expected.
So, is there life on Venus?
No one is saying that as of now. What scientists have discovered is the presence of a chemical which is known to be produced only through biological process, and not through any naturally occurring chemical process. There are some other ways in which this chemical might be produced, for example, in the underbelly of volcanoes or meteorite activity, but that would have shown in much lower concentrations. In any case, scientists have ruled out all those kinds of known possibilities which could be attributed for the presence of that gas.
In fact, this discovery was made in 2017, and the scientists checked and re-checked their data over the last three years before deciding to make it public.
The abstract to their paper in Nature Astronomy says this presence of phosphine is “unexplained” after an exhaustive study of all the possible other sources and “production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteorite delivery”.
So, the only possible explanation for the origin of this phosphine, based on our current knowledge, could be in the biological processes, the way it is produced on Earth, by some microbes.
During an announcement on Monday, scientists were very careful to emphasise, repeatedly, that this was not a confirmation of the presence of life on Venus.
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Why is it significant then?
This is the most credible evidence yet for the possibility of life away from Earth. Scientists say it is more significant, for example, than the discovery of water on the Moon or Mars.
“In the search for extra-terrestrial life, this is the biggest finding, no doubt. Of course, this cannot be taken to mean that there is indeed life on Venus, or anywhere else, but if you are a scientist looking for life-forms on other planets, I think this is your first real breakthrough,” said Dibyendu Nandi of IISER, Kolkata.
This is how Professor Sara Seager of the Department of Physics at the Massachusetts Institute of Technology, who is one of the authors of the study, also described the finding. She said the detection of phosphine had raised Venus “higher up on the ladder of interesting targets” where the possible presence of life-forms can be explored.
But Venus cannot support life, can it?
There are several things that we know of about Venus that make life, as we know it, unsustainable on that planet. The temperature of Venus is too high, and its atmosphere is highly acidic, just two of the things that would make life impossible.
But Somak Raychaudhuri, director of Pune-based Inter-University Centre for Astronomy and Astrophysics, suggested that this phosphine could be remnants from a time when Venus was a much more hospitable place.
“Look, this finding opens up many interesting possibilities. We don’t know how long phosphine molecules survive. Also, we know that Venus has not always been as inhospitable as it seems now. So, one of the possibilities, if we would like to explore the question of presence of life on Venus, could be whether this phosphine is actually something remaining from a time when the planet did support life-forms. These are open questions right now. All these will be explored. What we have got now is just a foothold in the door. We can now probe with greater enthusiasm,” he said.
“I would personally not classify this discovery in the same league as the discovery of the first planet, or the recent confirmation of the gravitational waves, for example, but it also certainly not as insipid as some signal of water molecule being found on some planet. In fact, in that way it is bigger than evidence for water. Water is only circumstantially related to life. It is not produced by life. Phosphine is produced by biological processes. So this is significant no doubt, and nothing like this has been discovered till now,” he said.
Varun Bhalerao of IIT Bombay said it was too early to consider this as evidence for extra-terrestrial life. “If you look at the paper they have published, the scientists themselves say something like, look we have found phosphine, but we don’t know whether it means life. It is very interesting, and extra-terrestrial life is certainly plausible, but based on this finding, I don’t think I would hold my breath for microbes on Venus, just yet. Plenty of weird molecules have earlier been found in weird places in space, where they were not expected,” he said.
What can this mean for Venus missions?
The finding can further ignite interest in space missions to Venus. Missions to Venus are not new. Spacecraft have been going near the planet since the 1960s, and some of them have even made a landing. In fact, the Indian Space Research Organisation (ISRO) is also planning a mission to Venus, tentatively called Shukrayaan, in the near future. As of now, the plan is still on the drawing board.
All future missions to Venus would now be attuned to investigating further evidence of the presence of life.
This article first appeared in the print edition on September 15, 2020 under the title ‘Reading life signature on Venus’.
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