Green face, long skinny body, slit eyes and skin like a melted marshmallow …

What’s your image of an alien??

  • A person with weird eyes, as seen on the 'X Files'.

  • That thing in ‘The Abyss’?

  • An oozing killer-blob? (really old movie called ‘The Blob’)?

  • A giant hairy insect (‘Lost in Space’)?

  • A skinny humanoid with a bulging visible brain ('Mars Attacks')?

  • Or a sinister micro-organism that creeps up on people’s ankles and infects them … (‘Dr Who’????)?

Considering we‘re not even sure if aliens exist, there are a lot of ideas about what they might look like. What do scientists think they might look like?

What would an alien look like?

First up, if the planet the aliens live on is anything like our Earth, it could be home to a huge diversity of life-forms. In that case, you might expect the aliens to come in a wide range of shapes, colours and sizes. After all, the Earth is host to everything from polar bears to slugs to flowering geraniums.

Planet size is a factor

According to an article in Discover magazine, the size of a planet would be a factor.

‘On a very large planet with 10 times the gravity of Earth, it’s hard to imagine anything growing up in three dimensions, because the gravity would be so powerful. On smaller planets you can imagine big bulbous things’, said Ken Nealson, head of the Astrobiology Unit at NASA [1].

But in fact, if you want a mental image of what scientists say is the most likely form of alien life, you need to think microbes!!


Yup, we’re talking about bacteria and other microscopic ‘blobs’ of life.

Why microbes? Because according to scientists, that’s what early life looked like on Earth. ‘You need to have a vast amount of time to let evolution ramp up to animals, and we think there are only a small number of planets where that could happen,’ said palaeontologist Peter Ward [2].

What’s more, our experience on Earth indicates that microbes seem to be able to survive in a huge range of environments!!

At home in boiling sulphuric acid

Scientists at NASA say they even know of microbes that thrive in boiling sulphuric acid … which is the type of environment that can also be found on Europa, one of the moons of Jupiter. (More on this)

And what do they look like?

As for their appearance, they add a red tinge of colour to some rather ordinary-looking rocks … which in my opinion is a bit of a let-down compared to the fully mobile, hyper-intelligent, super-communicative, space-shuttling, extraterrestrials that generally get into the movies.

Perhaps they could audition?

Cue the invasion of the killer red-tinge!

Writer: Berry Billingsley


[1] Glausiusz, J ‘Alien Investigator’, Discover, http://www.findarticles.com (August 2000)

[2] Boyle, A ‘Technology: Looking for life’, MSNBC, http://stacks.msnbc.com/news/362046.asp (26 January 2001)

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Written and project managed by Berry Billingsley for the Department of Education