From little green men to the crustacean-like 'prawns' of 'District 9' and H.R.Giger's nightmarish creation in the 'Alien' films - our appetite for imagining how visitors from another planet might look shows no sign of diminishing.
According to a British satellite expert and government adviser, however, the outlandish imaginings of Hollywood may not be quite alien enough.
Dr Maggie Aderin-Pocock - a leading scientist at European space company Astrium - has suggested that, far from being little green men, aliens could actually look like giant jellyfish.
The bizarre creatures the British scientist has dreamt up are she says an example of life "not as we know it".
The aliens she imagines are the product of what evolution might create on a world such as Saturn's moon Titan.
She imagines aliens that drift through methane clouds scooping up chemical nutrients into their mouths.
The creatures could also be able to live off light taken in through their skin, says the scientist.
The alien jellyfish - which Dr Aderin-Pocock imagines could be the size of a football field and have an orange underbelly - would be generated from silicon as opposed to carbon, which is the basis of all life as we know it.
The orange underbelly could act as a camouflage allowing them to evade would-be predators.
The aliens are kept afloat by onion-shaped buoyancy bags that dangle from their body, taking in or letting out gas in order to gain or lose altitude.
She also suggests they could communicate using pulses of light.
Dr Aderin-Pocock, who was describing her alien as part of Science Month on TV channel Eden, says much of her inspiration comes from the bizarre life-forms discovered deep beneath the ocean.
She 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 evolving on other planets in environments very different to our own.
“My vision of aliens is an inhuman, silicon-based life form that looks much more like a jellyfish than sci-fi’s little green men.”
“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.
“Maybe life doesn't have to resemble anything like DNA at all.”
Based on the latest discoveries of star-orbiting planets, Dr Aderin-Pocock believes there could be as many as four intelligent alien civilisations in existence in our galaxy.
But due to the distances involved, she believes we are unlikely to ever encounter 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.”
Her imagined extra-terrestrials would also not be able to survive if they visited earth - finding the damp oxygenated atmosphere lethal.