If such a planet had Earth size moons, we'd see not Europa and Callisto but worlds with rivers, lakes and all sorts of habitats - a surprising scenario that might just be common.'

Yeah, I want to live where there's 50ft tides, or maybe where day and night last for years at a time if the moon is orbiting a sideways planet like Uranus.

Aren't Jupiter sized gas giants bathed in ionizing radiation? Is there a safe zone for it?

Also aren't all those moons tidally locked and very small compared to terrestrial planets?

Have we found one of those moons that wasn't jammed with radiation that had plate tectonics or a magnetic field? Io is geologically active, but it's a little TOO active and it's also awash in radiation.

Why are none of the obvious cons mentioned in these articles?

OH we found a Jupiter sized planet in a habitable zone! I'll bet they have blue feline looking primates there that fly on lizards!!!

An earth sized tidally locked moon around a gas giant could still have a magnetic field because it spins on its axis once per orbit

An earth sized tidally locked moon around a gas giant could still have a magnetic field because it spins on its axis once per orbit

Have we ever seen an Earth sized tidally locked moon around a gas giant? Do we even have any simulations that suggest how likely such a thing would be?

I appreciate skepticism, but the tone of some of these comments seems to indicate a strong desire that nothing be found.

I appreciate skepticism, but the tone of some of these comments seems to indicate a strong desire that nothing be found.

Quite the contrary. The comments indicate a strong desire for realistic and honest reporting regarding these matters. Nothing would tickle me more than finding a universe teeming with life, especially intelligent life. My wanting it has nothing to do with the cold hard facts however.

We are just barely scratching the surface of this. Yes we should be hopeful, but we know so little right now that every discovery is important and interesting. Dont forget that we are just looking at things in our galaxy, and there are billions of galaxies out there. So as far as I'm concerned, if it is possible, it probably exists somewhere in this HUGE universe. There should be no doubt at all that somewhere, either in our galaxy or others, there are habitable moons. Where do you think Ewoks come from?

Dont forget that we are just looking at things in our galaxy, and there are billions of galaxies out there.

Billions of galaxies and isotropy everywhere. There is generally nothing fundamentally different anywhere else that we can see than here. What we find here is therefore highly likely to be representative of the entire universe. And scratching the surface or no, what we're seeing isn't all that encouraging to me. Perhaps I'm missing something...

Well perhaps I should qualify that. It's encouraging for finding simple life, not complex life.

If such a planet had Earth size moons, we'd see not Europa and Callisto but worlds with rivers, lakes and all sorts of habitats - a surprising scenario that might just be common.'

Yeah, I want to live where there's 50ft tides, or maybe where day and night last for years at a time if the moon is orbiting a sideways planet like Uranus.

Life will find a way. If day lasted for years, couldnt you just always keep on the move and stay in the daylight? Marine life could, and birds, too. As many crazy and interesting life forms we have on earth, little things like that wouldnt stop life from finding a way.

If such a planet had Earth size moons, we'd see not Europa and Callisto but worlds with rivers, lakes and all sorts of habitats - a surprising scenario that might just be common.'

Yeah, I want to live where there's 50ft tides, or maybe where day and night last for years at a time if the moon is orbiting a sideways planet like Uranus.

Life will find a way. If day lasted for years, couldnt you just always keep on the move and stay in the daylight? Marine life could, and birds, too. As many crazy and interesting life forms we have on earth, little things like that wouldnt stop life from finding a way.

There is good evidence that life began here in tide pools. Would 50ft. tides even allow for abiogenesis? Perhaps it would. And I agree that life "finds a way" where it can...but speaking for life as we know it there are times when life simply can't find a way. Those are the variables we don't know, but should be conservative in our estimates.

Here is the fundamental question:

We can all agree that a planet doesn't have to be a carbon copy of Earth to have complex life.

The question is HOW CLOSE to a carbon copy does it need to be to have complex life. Every single variable that isn't the same may be trivial or may even SEEM trivial, but easily could be all important. Also the more we learn the more variables we see and the more we see are indeed crucial.

And scratching the surface or no, what we're seeing isn't all that encouraging to me. Perhaps I'm missing something...

Well perhaps I should qualify that. It's encouraging for finding simple life, not complex life.

The sheer volume of the universe is encouraging to me. If we exist, then so do other intelligent life forms. The universe seeks to know itself, it will try to do this in many varied forms. Life is, after all, simply a complex mechanism for more efficient energy transfer. The rules that created life here are or should be the same in other parts of the universe, therefore undoubtedly there is intelligent life in the universe.

The sheer volume of the universe is encouraging to me. If we exist, then so do other intelligent life forms.

Volume can't account for everything. Do you believe there is an EXACT copy of Earth out there somewhere down to the atom? If you don't then you have to admit the possibility that the conditions for life MIGHT be so rare as to intelligent life being singular. If the universe isn't infinite, then there is a real possibility that there are no other intelligences.

I personally don't believe this, but I do admit the possibility. Volume isn't an argument, it's a condition.

The universe seeks to know itself,

???

Does it?

The rules that created life here are or should be the same in other parts of the universe, therefore undoubtedly there is intelligent life in the universe.

That's pretty spurious logic. One could easily reverse it as well if you think about it.

Of course we exist, and so do other life forms. They all want to find water, and after they turn that page, anything can and does happen. Look at Miranda, that ice ball showing evidence of massive removal of ice from huge mining operations from space(!). Few minds can conceive of machinery that colossal, and all for water.

No reason for extreme tides on a tidally locked moon. The tides will stay in one place, so the moon just won't be perfectly round.

This would be an interesting place for a society to develop... you can't see the gas giant you orbit until you have the ability to sail on the ocean that is most likely accumulated on the tidally locked side. If they start with a "flat earth" perspective, they'd think they were on an island surrounded by sea and the progressive revelation of the gas giant on the horizon would be quiet a sight. (and difficult to interpret!)

Since ~ 50 % of the known habitable planets (4 of 10) circles stars with 2 habitables, the traffic jam is already there. But it is very nice to see these types of planets too. The HEC lists candidate habitable moons.

As for looking at the worst constraints, it is not the point and it is not "realistic and honest reporting" but obscurantism if not ignorance. This result bumps up eta, # of habitables/ stars.

@ModernMystic: On honesty vs obscurantism, see above.

Tens of meters of tidal waves is not a problem, remember that Earth had it too under the early close Moon and had tides ~ 10 times higher than that (~ 100 m instead of a few m).

The dominant hypothesis right now is that life started in hydrothermal vents. Alkaline vents provides the necessary CHNOPS elements redox energy thermal cycling for initial replication.

The "random chance" idea of Monod is stupid. It doesn't describe a proper stochastic process, but is analogous to a dynamical process in a vast phase space that returns often and has a minute volume for success.

Model it as a stochastic process of abiogenesis attempts, simplest by a Poisson process, and the likelihood is ~ 100 % life on > 7 billion year old habitable geoactive planets given our observations here.

The dominant hypothesis right now is that life started in hydrothermal vents.

Indeed. This is my view as well, but no one knows "for sure". In any case as a general rule it's more difficult for smaller celestial bodies to produce life in thermal vents as they're going to lose their internal heat quickly. Gravitational "kneading" by a gas giant can help with this "problem", but it seems to help "too well" in some cases (like Io).

This may not matter however, as life appeared on Earth quite "quickly" relatively speaking and you may only need the internal heat to "jump-start" abiogenesis. OTOH what happened here on Earth may be a complete fluke and it usually takes 4 billion years for life to even begin. We simply don't know.

What we DO know is that the equation is far more complex and has far more limiting variables than Frank Drake postulated....

The dominant hypothesis right now is that life started in hydrothermal vents. Alkaline vents provides the necessary CHNOPS elements redox energy thermal cycling for initial replication.

I would throw in that we have found seemingly ancient bacteria living off of radiation in the Earth's crust (Example: Deinococcus radiodurans). I'm beginning to suspect that this 'near surface' evolution of life might be a biased way of looking at things (emphasis on: "might"). Maybe life didn't move down, but up out of the crust?

The earth's crust certainy holds the materials of life in abundance at any depth - and energy in form of heat/radiation is ubiquitous down there...and was long before the oceans ever formed.

If that is the case then (bacterial) life in the interior of planets may be far more common than we think. Because while energy on the surface may not be available on all planets - radiation on the inside certainly is.

I'd like to point out a few things.

1. (Con) I think the 'skeptics' here are merely pointing out, that our current knowledge of our own gas giants, shows them to create a zone of high radiation that is very hostile to potential surface life on a moon.

However, consider a neptune sized giant with an earth sized moon? I think there are *Some* scenarios that may negate this concern.

2. (Neutral) For an earth-like moon around a gas giant, tides would be invariably extreme, and while it would not rule out life, it would certainly change some of the rules in unexpected ways.

They would also ebb and flow over the course of months not hours

3. (pro) I would point out, that a tidally locked moon would counteract tidal locking with a small star in the habitable zone and therefore potentially moderate some potential extremes that would exist for life around a small star. A month long day and a night with a large amount of planetshine is probably more conducive to life than extreme constant

Edit for above - Ah, someone else is correct, there would be no massive tides, because the large tide would not move. There would only be a small solar tide.

The large tide would be "locked" derpy derp. lol

Not a new idea read the sci-fi novel When Worlds Colidie publish in 1934 a gas giant with a earth size moon.

nkalanaga: I just pitched my idea via email to a producer I know. Thanks for the nudge!

Radiation? Atmosphere should protect against that.
Tides? Unless cause too strong volcanism don't seem much problem.

So here more serious obstacles:
Mass - there would be indeed plenty of moons in HZ, that in overwhelming majority would be too light to maintain atmosphere
Planet migration - assuming that something Jupiter like migrated inward, its moons would actually turn out to be mostly ice that would melt. There would be no rivers or lakes, there would be one, hundreds kilometres deep ocean with no island
Length of day - that moons would be tidally locked to their planet. Consequently their day would be at least few days long, which would bring huge temperature amplitude

So for aquatic life seems acceptable, though evolution of a bright land specie might be harder.