Even Dr Who might be taken aback at the sight of these aliens.

The bizarre, jellyfish-like beings were dreamed up by a British scientist as an example of life “not as we know it”.

This is what evolution might have come up with on a world such as Saturn’s moon Titan, Maggie Alderin-Pocock believes.

She envisages creatures that float through clouds of methane, scooping chemical nutrients into their gaping mouths.

The aliens keep themselves aloft by means of dangling onion-like buoyancy bags and communicate with pulses of light.

Dr Alderin-Pocock, a leading scientist at European space company Astrium, said: “Our imaginations are naturally constrained by what we see around us and the conventional wisdom has been that life needs water and is carbon-based.

“But some researchers are doing exciting work, playing with ideas such as silicon-based life forms.

“Silicon is just below carbon in the periodic table, has some chemical similarities and is widely available in the universe.

“So perhaps we could imagine similar instructions to DNA but with silicon.”

Her aliens would probably die on earth, finding the damp oxygenated atmosphere lethally corrosive. Equally, humans would not survive on Titan.

Based on the latest discoveries of star-orbiting planets, she also believes as many as four intelligent extra-terrestrial civilisations could exist in our galaxy, the Milky Way. But they are so far away it is unlikely we will ever meet them.

“The Voyager 1 spacecraft, which is carrying a recording of greetings from earth in different languages, has been travelling through the Solar System since the 1970s and has only just made it into deep space,” she said.

“To get to our nearest neighbouring star, Proxima Centauri, would take it 76,000 years.”