By Joe Campbell
BBC News Magazine
Astronomers think they may have struck gold in their search for a planet beyond ours that could sustain life, but just what kind of neighbours should we expect if they come calling?
Whether they are little green men or the grey, bug-eyed aliens beloved of those who live in hope that we are not alone, the one message all the scientists can agree on is do not hold your breath waiting for their knock at the door.
At a distance of more than 20 light years from Earth, Gliese 581c is not exactly on the doorstep.
Life out there may not resemble anything we've seen before
So far we know it is about three times the diameter of the third rock from our sun and just like our home, it lies in the so called "Goldilocks Zone", that relatively narrow band of space around a star that is neither too hot nor too cold for us to hope that life may have evolved there
Ask the experts what life may be like and that is where the disagreements start to emerge.
"The planet may be habitable, but I wouldn't expect to see any intelligent life forms, " says Martin Griffiths, senior lecturer at the Centre for Astronomy and Science Education at the University of Glamorgan.
"We might see bacteria or something like that. You have to consider that for three billion years of our own evolution, the entire continuum of life here was microbiological, so I'd expect to find something like that."
Down the years most of our images of alien life have come not from the world of science but from the field of entertainment.
Scientific speculation has led to the appearance of everything from airborne jellyfish drifting through alien skies to heavily armoured crab like creatures scuttling across deserts warmed by distant suns, on television and cinema screens.
Hollywood and home-grown depictions of extra-terrestrials maybe be dismissed by the world of science, but Dr Jack Cohen, author of the book, What Does a Martian Look Like?' says fellow academics are probably no closer to the truth.
"We're limited by our imaginations in a way life on alien worlds certainly wouldn't be," he says.
"If you ran the Earth again as an experiment, you wouldn't get humans. What a planet is like doesn't determine what the evolution will be like."
What scientific speculation there has been, he compared to the early fossil hunters who devised entire creatures from a few scraps of a skeleton - often producing creatures that seem almost comic in the eyes of today's dinosaur experts.
'Expect the unexpected'
Dr Cohen says life on other worlds might be so completely different to anything humans have knowledge of, it might not even be recognisable to us as life.
Professor Mark Brake, who helped set up the first course in Britain into the study of astrobiology says we are no closer to finding out what life of other worlds might be like than when the Greek satirist Lucian first speculated on the idea around 100AD.
"My first thought on all this is a line from The Hitch Hiker's Guide to the Galaxy that you should expect the unexpected," he says.
Would aliens be hostile?
"Whatever life out there looks like, it's more likely than not it won't be anything like us at all."
Any life forms would have evolved to deal with the planet's gravity which would be around one-and-a-half times that of the Earth's, because of its greater mass.
Does that mean any extra-terrestrial visitors from the newly found planet would be able to leap tall buildings here on earth like Superman, that other product of a high gravity alien world?
"Going to visit them would certainly make us feel heavier and it would take more effort just walking around," says Martin Griffiths.
"It wouldn't have a substantial effect on us in the short-term, but if we stayed we'd probably evolve ourselves into people who were short and squat."
Voyage of discovery
The only way we will ever know for certain whether life exists on this new super-size Earth will be to go there, and with current space exploration technology that won't be happening any time soon.
"I just wish I was alive to see that day," says mathematician and part-time sci-fi writer, Professor Ian Stewart of the University of Warwick.
But like many interested in the relatively new science of astrobiology, he is travelling hopefully on the still Earth-bound voyage of discovery.
"A few years ago we couldn't find planets out there, then the ones we could see were too big to support life and now we've found one that's almost Earth size so at least I've lived to see that."
Add your comments on this story, using the form below.
Why does everyone insist life forms on a different planet would be so radically different from those of our own? Just look at the diversity of life forms here on Earth, from creatures with no legs to those with hundreds, from those living in extreme cold to those in extreme heat. It could be that there are certain optimum forms that evolution strives towards given certain environmental conditions, in which case could we not expect to see familiar life forms from amoeba-like to fish-like to reptile-like to mammal-like and even human-like
Zaphod Beeblebrox, Magrathea
Think how big a DNA molecule is. Then think how likely it is that an alien planet has replicated DNA exactly. RNA, Chlorophyll, Haemoglobin & proteins are not exactly small molecules either. There is almost no possibility that alien life has replicated the biochemistry of life on Earth.
Mark Kidger, Madrid, Spain
If it might not even be recognisable to us as life - what's to say that life exists on earth that we don't recognise either?
Ash Thomas, UK
Why do you bother publishing this rubbish? The planet has not been directly observed, if it exists it is most probably tidally locked (i.e. it permanently presents one face to the sun) so one face is frozen and the other is extremely hot, its existence is postulated on there being a fourth planet in the system whose existence has been assumed, any events which can be viewed from Earth happened 20.5 million years ago, if the astronomical distances can be believed, we do not know whether it or its star even still exist and we cannot ever get there to find out.
Of course we're not alone in the universe. With the universe so unimaginably huge and still expanding from the big bang, it would be arrogant in the extreme to believe we are the only intelligent beings in it.
Jay Brown, Portsmouth, UK
I do agree with Dr Cohen when he remarks "We're limited by our imaginations in a way life on alien worlds certainly wouldn't be,".
There could be dimensions that are invisible to us and other forms of intelligence that are incomprehensible to us.
This universe is so vast, that we cannot be the solitary intelligent beings around. Maybe the life exists in a form yet unknown to us. Is it or could it be really life?
Arun Dhadwal, Aix en Provence
In all science fiction, aliens are generally depicted with 2 eyes, nose and a mouth, I think we are going to be in for a stock when we actually see life from another planet.
Nick Farina, Liverpool
I've been visiting your planet for some time, and I'd just like to say how disappointed I am that my wonderful home is given a pretty miserable label of Gliese 581c! Is 'alien' life hostile?! We are if you don't start calling it by it's proper name of GhrsSSYdzklflapp!
Fleep Bloort, Nottingham, UK, Earth, Milky Way
How on earth (pardon the pun) can scientists determine the atmosphere of a planet approx 20 million million miles away when we have difficulty getting reliable weather forecasts for the next couple of days?!
A. Sceptic, Wigan/UK
I think it's worth pointing out that radio communication with this planet would travel at the speed of light (as you say), and so we would be waiting 40 years for each reply - and that's assuming that we could even make meaningful contact. Travel times are much higher - the fastest speed ever attained by a manned spacecraft is about 40,000 kph (Apollo 10's re-entry), so even if we could achieve that speed for the entire journey, it would still take about 550,000 years to get there. Even transmissions from an unmanned probe would take 20 years to reach us, and that's not including the travel time for the probe to get there. This seems to me like a story that is of human interest, but has no practical implications. Call me a cynic, but I don't think anything meaningful will come of this.
Lee Clarke, Southampton, England
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