BBC Focus Magazine

[Jamie]

http://www.bbc.co.uk/news/science-environment-15863549

Scientists have outlined which moons and planets are most likely to harbour extra-terrestrial life.

Among the most habitable alien worlds were Saturn's moon Titan and the exoplanet Gliese 581g - thought to reside some 20.5 light-years away in the constellation Libra.

I must admit, I find it a bit odd that Titan is ranked higher than Mars in the 'Planet Habitability Index'. It doesn't explain why, I'll have to do a bit of research.

[M Paul Lloyd]

I think its because Titan has a proper atmosphere Jamie, but I could be wrong.

[Isee]

It's got clouds, a weather system, seasonal changes, and most importantly liquid stable bodies. the only in the solar system other than earth.

At this rate the question should be, "do you believe that there are NO aliens out there?". We once thought we had the whole world mapped out and then stumbled upon Americas, it wasn't magic and it wasn't hard to explain. But only AFTER we had discovered it. I would not be surprised if the same happens with extraterrestial life. We will discover something in our own backyard and then wonder how we had missed it before, because it was bleedin obvious! Will proabbly happen in the next 50 years too!

[Isee]

Just had a closer look at the article. Gliese 581g - rated at 0.89 .
With earth being 1, Are we really saying that Gliese 581g is 89% like earth just from having measured an incredibly distant and minute light twitch???

While I don't doubt there are incredibly similar planets out there to our own, i have to question this enthusiasm of ranking, something like the 20th exoplanet ever discovered to be so hospitable to life.
Because under normal distribution this would imply that every other star out there has a habitable planet...

[Shadowwolf]

It's from the light that they have been able to get enough of a picture about its location in the system and from this are able to make some educated guesses as to its habitability.

However, it would seem that the place does not exist, at least according to these folks.

Because under normal distribution this would imply that every other star out there has a habitable planet...

Not really, even were habitable planets extremely rare we are as likely to find one in the first twenty as we are at any other point.

[Isee]

It's from the light that they have been able to get enough of a picture about its location in the system and from this are able to make some educated guesses as to its habitability.

However, it would seem that the place does not exist, at least according to these folks.

Because under normal distribution this would imply that every other star out there has a habitable planet...

Not really, even were habitable planets extremely rare we are as likely to find one in the first twenty as we are at any other point.

yes but we've already found like a dozen out of total of what? 50? so again from the sample we can make an educated guess at a population.

[Jamie]

Guess I was thinking about more earth type, water-based life. More chance of that on Mars.

Any life on Titan would have to be pretty different to any found here.

[Shadowwolf]

yes but we've already found like a dozen out of total of what? 50? so again from the sample we can make an educated guess at a population.

Sorry, I thought you were suggesting they were rare and thus we should not have expected to find any so quick.

[Isee]

yes but we've already found like a dozen out of total of what? 50? so again from the sample we can make an educated guess at a population.

Sorry, I thought you were suggesting they were rare and thus we should not have expected to find any so quick.

I don't know what I was suggestign anymore

Just saying we found at least one that is 89% similar to earth relatively close and pretty much on the first attempt at searching. Given that sample, either we have ranked overly earth-like, or there are earths all around us pretty much, and to to expect to be alone in the universe would be extremely arrogant.

Given that we have not had artificial lights, radio waves, or objects sent our way, we are either the first sepcies to evolve to this level of intelligence in the universe or perhaps the planet in question was just ranked over optimistically...

I tend to lean towards simpler and more likely solutions and won't be breaking that trend now either

[Shadowwolf]

Given that sample, either we have ranked overly earth-like, or there are earths all around us pretty much, and to to expect to be alone in the universe would be extremely arrogant.

Well just remember that this classification of Earth-like is mostly bound up by the planet in question being in a specific orbital zone. It says nothing about whether or not the planet is actually habitable and certainly nothing about whether life is present on it or not.

Given the sheer number of galaxies, stars and planets out there, that life can form as it has self evidently done, the idea of being alone is rather unlikely.

Given that we have not had artificial lights, radio waves, or objects sent our way, we are either the first sepcies to evolve to this level of intelligence in the universe or perhaps the planet in question was just ranked over optimistically...

It's not as simple as it might appear. We can only say that for the very short spell that we have been capable of detecting such we have detected nothing - there was the Wow signal mind - but that is insufficient information from which to suppose that we are thus first, alone or mis-ranking planets. As I alluded to above, just because they may be in the habitable zone does not mean that they are habitable, have life and especially intelligent life technologically advanced.

Oh and if it is Gliese 581g you speak of, well it might not actually exist anyway.

[MikeG]

Titan is a strange case. Its only the size of our own moon, which means one-seventh the gravity of the Earth. And yet it can maintain an atmospheric pressure 1.5 times that of Earth. It seems to have organic compounds in its atmosphere, and a high nitrogen content. It makes you wonder why Mars, which is so much larger than Titan, and which apparently had a viable enough atmosphere and weather system to produce severe Earth-like erosion, lost its own atmosphere.

[Jamie]

I think it's because it's colder. The gas has less energy making it more difficult to escape. I wonder if Jupiter's magnetic field helps too?