It's an extraordinary possibility - the idea that living organisms are floating in the clouds of Planet Venus.

But this is what astronomers are now considering after detecting a gas in the atmosphere they can't explain.

That gas is phosphine - a molecule made up of one phosphorus atom and three hydrogen atoms.

On Earth, phosphine is associated with life, with microbes living in the guts of animals like penguins, or in oxygen-poor environments such as swamps.

For sure, you can make it industrially, but there are no factories on Venus; and there are certainly no penguins.

So why is this gas there, 50km up from the planet's surface? Prof Jane Greaves, from Cardiff University, UK and colleagues are asking just this question.