We have no idea of the scale of our ignorance so it surprises me that anyone, no matter how eminent a scientist, can come to any conclusion about this.  Human beings have existed for a blink of an eye, so give it another 20,000 years and see what we think then.

Another reason for lack of contact could also be that technologically advanced civilizations simply don't last very long, the likelihood of self destruction, disaster or annihalation by natural forces is much greater.

Dr Who writers have a vivid imagination.

The Moon is actually an egg that has taken billions of years to hatch.

Brian Cox says that we may be the only intelligent life in the galaxy but that there will be single-celled life "all over the place"

I'm in this camp even though there is no evidence to back up my claims. I think the Universe is rife with life but beings capable of space travel are so rare, we may be the only one on in the galaxy (not Universe). I think there's a very good chance of life on Europa, Callisto, Enceladus even deep down on Mars as all the ingredients are there. Defining life is also hard, is a virus alive? Scientists are having a hard time defining it but I'd suspect it will arrive anywhere there is water, energy and enough time. The Universe is so huge that it's almost a certainty.

Also think about a World like Europa. It's covered in a 20km think layer of ice. There is most likely deep sea vents and an ocean under this crust so there's a fair chance it will arise but any potential life will have no chance of attaining space travel. We've also had means of communicating in space for 100 years, that's one 5 millionth of the age of the planet, that's a very short period, maybe every advanced species ruins it's planet by over population and using all it's resources. For all we know Mars and Venus could have been just like the Earth millions of years ago.

New Horizon reaches Pluto next year but already we know there is something very strange about this world. Some have calculated there could be an Ocean on Pluto as it's tidally locked with it's Moon Charon. This place is more like a binary planet than a planet/ moon system. With such frequency of possible life in our own Solar System, I'm very optimistic of life being found elsewhere even in my own lifetime.

I'm pretty convinced that the preconditions for life have at some point existed on Mars.

Its surface features strongly suggest that water has flowed across it, which in turn points to it once having had a dense enough atmosphere, and thus the requisite atmospheric pressure, to retain that water. My own belief is that it was hit by a large ferrous body, whose impact and its consequences burnt away the atmosphere. This would result in the almost instantaneous boiling of any water on Mars and of course, due to the loss of atmosphere, the dissipation of the steam from that water.

This theory also explains the red dust which thickly coats the planet's surface now.

Current theories about Enceladus, well studied in recent years by Cassini, suggest that it is also a prime candidate for life. Hubble has also detected water-vapour plumes on Europa, which I believe the European Space Agency is planning to visit some time in the 2030s.

If it's so straightforward, why has life arisen only once on this planet, and not twice or a million times?

We can't even define life nor an intelligent species, we're very new to all of this so give it time. When we fully explore the Solar System in the next 1,000 years then we'll have a better idea. I'm not hopeful for the planet but getting off it has been a major achievement so maybe there is some.

The older I get the more I lean towards the opinion that there may be some sort of creator or creative force

Nice sentiments but the ingredients of life are the Universe over. Besides, who created the creator?

If there's life out there, Jim, but not as we know it, why isn't it also here on Earth? Go to the most extreme circumstances, ranging from half a mile beneath the bed of the deep ocean to areas bathed in radiation, and the only life you'll find is microbes sharing the same origin as ourselves. Nothing else after 4 billion years of extreme changes.

Incidentally, what makes you unhopeful for the planet? What is evolution other than proof that life adapts to anything? 99.9% of all species that have existed are estimated to have gone extinct, which is precisely why the life which has taken their place on the Earth today comprises species of such resilience.

We should fire off some rockets full of random bug and microbes to likely planets

The sun will burn out eventually and we become a cold stone, enjoy while you can

well this thread has been a decent read. some good points and some not so good. however you may have guessed that i'm only breaking my silence here to point out that....

it is the basis of Christian belief that we are alone in the universe because God created human life on this planet only.

this is absolutely untrue, there's nothing in the bible to suggest that human life is unique to this planet, never mind any other form of life - only that we here were made as God's special race. its precisely for this reason that God, whether you believe in him or not, is an irrelevance to this debate.

personally I think there's probably life under that ice sheet on Europa although its probably unlike any hypothesis anyone has or will ever make. i like to think of a race of sharks living under there with human like intelligence

And its shocking omission that no one answered..

"Who here believes in aliens?"

with...

"I want to believe"

Night all

Loving the comments below the video lol.

FANCY FLYING ME ALL THE WAY TO THE EARTH WHEN WE COULD HAVE JUST FLOWN A FEW LIGHT YEARS AWAY TO ONE OF THEM NEW UP AND COMEING PLANETS

Do Wah spamming

OVAL MAN DONT BE A SQUARE

I KNEW IT I JUST KNEW IT ,WE SHOULD HAVE TOOK A LEFT AT PLUTO WERE GOING TO END UP NEAR THE SUN

NO I WONT SHUT UP ,YOU NEED TO STOP SOMEWHERE I NEED TO HAVE A WEE AND SOMETHING TO EAT

OK IM SORRY ,ILL BE MORE SENSIBLE WHEN I SEE A POST ABOUT ALIENS ,

OK IM SORRY ,ILL BE MORE SENSIBLE WHEN I SEE A POST ABOUT ALIENS ,

People say why waste money, we not sort this Earth out first

but judging by what I see...what chance have we got of doing that????

We are always looking to start wars, our population is out of control, we don't

know yet how global warming will affect us, we don't know if we can grow enough food for everyone, provide enough energy

We are better off looking for life on Mars imo

There could be alien life that cannot be picked up by science, maybe operating outside our range most of the time but occassionally coming across for fleeting moments.   Unlikely but not impossible.