An international team of scientists has discovered what could be signs of alien life, in the atmosphere of the planet Venus.

Research has detected copious amounts of phosphine in what's known as the 'upper decks' of the atmosphere. Phosphine is one of the most toxic, most horribly-odorous gases known to humanity. Frequenters of pond slime, rotting fish and other unfortunate phenomena will be familiar with the smell.

What is so significant about the find is that, whilst phosphine is made via human industry, it is also made as a by-product of anaerobic organisms, such as bacteria. The scientists, led by Jane Greaves from Cardiff University, explain in their paper 'Phosine gas in the cloud decks of Venus' - published today in the journal Nature Astronomy - that the sheer amounts of the gas cannot be explained by any non-biological process known to occur on Venus.

"Either phosphine is produced by some sort of chemical or geological process that no-one knows about – or there could be a biological reason," said Emily Drabek-Maunder, an astrophysicist from the Royal Observatory Greenwich and fellow author on the paper.

She continues: "Our study isn't conclusive that this is evidence of life. However, what is exciting about it is that we've found this rare gas in the upper atmosphere of Venus.

"Our team can't explain the amount of phosphine that we've found, through our current understanding of the planet. When we try to model what's happening in the atmosphere – volcanic activity, sunlight, or even lightning – nothing recreates the amount of phosphine gas that we've seen."

The team cautions thus that there is currently no way of knowing for certain what the findings truly mean: "is not robust evidence for life, only for anomalous and unexplained chemistry".

Venus' surface is extremely hot and acidic, making it extremely unlikely any life could survive there. Whilst acidity remains high in the cloud decks - approximately 35 miles above the surface - overall conditions are thought to be a bit more habitable. However actually, the high amounts of acidity are thought to be a key clue in the riddle - the acidity would mean any current phosphine in atmosphere would be destroyed quickly. Thus, there must be something actively producing such large amounts.

Other experts who were not involved in the research say they are "very excited" about the findings.

All experts of course stress caution and the importance of further extensive research:

David Clements, who works as a scientist at Imperial College London and is another author on the paper: "This isn't a smoking gun. This isn't even gunshot residue on the prime suspect's hands. But there is a distinct smell of cordite in the room."

Yet, there is a distinctive note of optimism within the team, and the wider scientific community:

"It's a possible sign of life," says Dr Helen Fraser, a member of the team and astronomy research at the Open Univesrity, "But the scientist in me becomes very cautious, and says that what we've discovered is phosphine", rather than a direct and absolute sign of alien life." But she noted that as you "peel back all the layers" of finding other explanations – which Dr Fraser described as an arduous process of examining and cross-referencing other existing research to understand if anything else could produce the levels of the chemical in question – one is left with the apparent-understanding that the simplest explanation is the only one that seems to remain: that there's phosphine producing life out there Jim, and not as we know it.

Future work will certainly be thrilling to await.

Fingers crossed.