Possibility of life on Venus: Remote hope with need for ample caution

Is there life on Venus? For many years, there was hope. Venus is a rocky planet. It is Earthlike in size and gravity. It has a thick atmosphere. However, those hopes were dashed in the 1970s when probes discovered its average surface temperature was more than 450 degrees Celsius and that its atmosphere was about 95 per cent carbon dioxide.
 

However, a paper released this week – “Phosphine Gas in the cloud decks of Venus” in the journal Nature Astronomy – has reignited the debate. A team of astronomers led by Jane Greaves of Cardiff University discovered that the planet has a high concentration of phosphine gas (Ph3). This is a gas composed by the combination of one atom of phosphorus with three atoms of hydrogen.
 

The scientists used the James Clerk Maxwell Telescope (JCMT) in Hawaii for five mornings in June 2017 for their initial data.

The JCMT is a radio telescope in the microwave range. When it “looks” at Venus (or any other object), the scientists can analyse which bandwidths are absorbed by the object, and this gives them an idea of what compounds are present.

The Venusian atmosphere is thick and opaque to normal light, which is why it’s dazzlingly bright. The multiple probes launched to the planet in the last 60 years have given us a picture of the “cloud decks” – multiple different layers of clouds in the atmosphere.

The team was surprised to discover a fairly high percentage of phosphine in the atmosphere. It took a long time to clean up the data and to confirm readings. In March 2019, they took a second set of readings using the Atacama radio telescope in Chile.

The data coincided with the first set. The paper records the testing of data in meticulous detail to rule out chances of error in detection.

Phosphine is present in the Earth’s atmosphere but in far lower concentrations. It is present in about 20 parts per billion in Venusian atmosphere and is about a thousand times less abundant on Earth. It is present in far larger quantities on the gas giants, Jupiter and Saturn, and quite probably on Uranus and Neptune (also gas giants but less studied).

Astronomers try and work out how any unusual compound is produced. Gases like phosphine and methane are classified as “bio-signature” because they can be produced by biological actions. On rocky planets like Earth, as far as we know, phosphine is produced in only two ways. One is in industrial complexes where it is synthesised as a base ingredient for rat poisons. The other is through micro-bacterial actions in oxygen-poor, hot environments.

The first option is exceedingly unlikely. The second – well, Venus is an oxygen-poor and hot environment. However, before going overboard and celebrating life on Venus, there’s need for ample caution.

It is known that phosphine is produced in vast quantities on the gas giant planets through non-biological processes. Jupiter and Saturn are balls of gas with no solid core. In the deeper layers of the gas giants’ atmospheres, high temperatures and pressures lead to the production of phosphine due to an abundance of phosphorus and hydrogen.

Those conditions are way different from the ones prevailing on Venus. But it is very possible, even likely, that there is a non-biological process we don’t know about operating on Venus to produce phosphine.

As the paper cautions, “Even if confirmed, we emphasise that the detection of PH3 is not robust evidence for life, only for anomalous and unexplained chemistry. There are substantial conceptual problems for the idea of life in Venus’s clouds—the environment is extremely dehydrating as well as hyperacidic. Ultimately, a solution could come from revisiting Venus for in situ measurements or aerosol return.”

We need to send another set of probes with experiments designed to focus on the phosphine anomaly.