New Find Boosts Prospects For Life On Distant Moons

sciencehabit writes "Imagine life on an Earth-like moon, one so close to its gas giant host that its landscape is bathed in a dusklike planetary glow. Such places are not only possible but also probable, according to a new study, which finds that as many as 5% of gas giant planets orbiting their stars at Earth-like distances may harbor habitable 'exomoons.' According to simulations, alien gas giants (like our Jupiter and Saturn) could pull in earth-like planets from the interior of their young solar systems. Though many of these planets would crash into the gas giants or later be flung into space, some would evolve stable orbits and stable climates, eventually setting the stage for life."

Comments

Err, waitaminute.

[Penguinisto]

...one would think that the radiation would pretty much sterilize any object that damned close, no?

Sure, there are bacteria that thrive in radioactive environments, but there's a diff between fissile waste and a massive gas giant's output...

Re:Err, waitaminute.

[newcastlejon]

What sort of radiation?

Re:Err, waitaminute.

[Anonymous Coward]

I think he means the radiation from the parent star, because most of the gas giants they have found so far are close to their parent star (makes it easier for us to find them).

If the gas giants have a magnetic field as strong as Jupiter's, a closely orbiting moon might well be shielded by it from a lot of the charge particles from the sun, much as our Van Allen belts do.

The UV, etc, is still going to be nasty unless the planet has an atmosphere that blocks a lot of that.

Re:Err, waitaminute.

[newcastlejon]

So, there's an Earth-like body, which I took to mean atmosphere, composition and climate, going round a star at an Earth-like distance. Is there any problem with radiation coming from gas giant nearby?

Re:Err, waitaminute.

[Lokitoth]

Personally, I would be much more worried about tidal forces. Though if it is far enough away from the gas giant...

Re:Err, waitaminute.

[moderatorrater]

Just like the intense heat of the yellowstone mudpots or the ocean volcanic vents would prevent life from being there? Or the extreme cold of the arctic? Or any of the other places that we thought life couldn't exist until we found it there?

Re:Err, waitaminute.

[That Guy From Mrktng]

Why do ET life research imply that whatever we should find must have the same weakness and conditions as found on the earth? The only thing in common should be evolution and if you start from some extreme conditions (extreme from our point of view) then you evolve your way around to them. Life that evolves from planet with strong gravity would be massive and strong, Life evolving in methane atmosphere would have bio-combustion chambers instead of lungs. etc.

It's like making first contact and waiting for the ETs to wear neckties and speak proper English, have some religion (God forbid an atheist ET) and be amused with the 3 stooges.

South park's Space Police anyone?

Re:Err, waitaminute.

[Anonymous Coward]

Actually, the radiation would likely aid evolution greatly.
It will create wild environments, things constantly mutating.
And, possibly, eventually create lifeforms that are heavily immune to the effects of radiation, probably even using and depending on it for energy.
Given time after this, it could lead to more complex life, possibly life that has smaller cells but larger numbers of them since larger structures are more likely to fail due to hue mutagenic damage.

It might not happen on the same time-scales of Earth, but we are but one reference point.
Evolution is heavily based on chance. The correct events in the right order. Considering the interactions end up being in the googolplexes or more per day on a planetary scale, that part can be ignored.
It is more about the ones that now survive. It could well be easy to create complex life, but it gets wiped out so many times that it might seem hard. Earth could well have taken longer to evolve complex life, it could be the earliest, we won't really know till we have more data, sadly.

This is why using Earth as the only reference point is hard to come up with concrete numbers.
I think we can all agree that Mars was probably alive at one point in the past.
That should be our main objective. That and Titan since that is of course one of the possible targets for this whole article.
The big ball of ice and water sitting out there another one. It won't be all ice, it will almost certainly have more minerals under it that, aided by radiation, could have evolved some life.
These are all places that almost certainly have some sort of early life on it, Mars possibly one that could have had complex life.
Of course, Mars has been rusted away to a big red ball, which all missions so far have apparently ignored. Any intact / fossils of life will be very, VERY deep underground.
Mars has been estimated to being ravaged by the suns radiation for several 100 million years now, if not longer. Image your typical lost cities covered in dirt and sands of various types, but much longer time-scales.
We really do need to go deeper. (yes, you were thinking that Inception noise)

Re:Err, waitaminute.

[Anonymous Coward]

I'm guessing he means radiation from the gas giant itself. The radiation near Jupiter is enough wreak havoc with or fry space probes. I'd imagine that wouldn't bode well for anything living.

Re:Err, waitaminute.

[Anonymous Coward]

Jupiter's magnetosphere produces intense radiations belts around the planet. All of Jupiter's moons are constantly bathed in enormous amounts of radiation.

Re:Err, waitaminute.

[todrules]

Or the fungus in Chernobyl that feeds on radiation.

Re:Err, waitaminute.

[Tsar]

Actually, there is no radiations there. Just a big magnetic field which would make it really hard for any kind of civilisation to get pass bronze age. I guess that's one more win for the Na'vi uh...

Actually, the massive magnetic field is the dynamo for trapping ionizing solar radiation and generating synchrotron radiation. That's why the Europa mission electronics have to be radiation-hardened beyond anything ever sent into space, and why your hypothetical Na'vi would never develop past an interesting self-perpetuating chemical reaction in some Jovian moon's primordial clays. Where's a hyperintelligent, near-omnipotent monolith when you need one?

Re:Err, waitaminute.

[MobileTatsu-NJG]

Or any of the other places that we thought life couldn't exist until we found it there?

Not quite. We're talking about life starting in an environment like that, not life evolving into that environment from a more comfortable one.

Re:Err, waitaminute.

[Anonymous Coward]

Or any of the other places that we thought life couldn't exist until we found it there?

Not quite. We're talking about life starting in an environment like that, not life evolving into that environment from a more comfortable one.

Live didn't start in a comfortable environment on Earth, at least not how you define it. In fact, life *created* your comfortable environment. All the oxygen in the atmosphere was put there by organisms that had oxygen as a byproduct of their metabolism. Aerobic organisms came later, once the atmosphere was rich with the gas.

Re:Err, waitaminute.

[MobileTatsu-NJG]

So the surface of Earth was below freezing or several hundred degrees until life took over?

Re:Err, waitaminute.

[1u3hr]

Actually, the radiation would likely aid evolution greatly. It will create wild environments, things constantly mutating.

No, that's comic book "science". Radiation isn't necessary to speed up evolution. There is plenty of variation already. Massive random mutations are usually simply lethal. Evolution proceeds via incremental changes. What speeds up evolution is an environment with unfilled niches -- see e.g. the Galapagos, where the relatively small number of animals (e.g. turtles) and birds (e.g.finches) that colonised it quickly evolved into numerous species to exploit different food sources, etc. Or how we mammals got our big chance when the dinosaurs were wiped out. All of that occurred without any "Incredible Hulk" style "mutated by gamma rays".

Re:Err, waitaminute.

[TapeCutter]

"In truly great magnetic fields like those of Jupiter, atomic particles may be heated to millions of degrees, and a great electric arc flows between the planet and its moon lo." - NASA

Re:Err, waitaminute.

[TapeCutter]

Single celled life appeared at the same time the Earth cooled enough to have a liquid ocean, multi-cellular life appeared several billion years later at the end of the last "snowball Earth" event.

Re:Err, waitaminute.

[moderatorrater]

Not quite. We're talking about life starting in an environment like that, not life evolving into that environment from a more comfortable one.

We have exactly one planet with one example of life starting. We have no idea what circumstances can lead to life starting. We do know, however, that life will fill pretty much any niche there is. With the lack of knowledge we have, it would be foolish to believe that we can rule out any environment as a possibility for life.

Re:Err, waitaminute.

[sunspot42]

A large moon (Mars sized or larger) would almost certainly be geologically active if it orbited a large gas giant. Indeed, even smaller worlds without a lot of internal decay heat of their own would retain a molten interior far longer than a lone planet the same size would, because of the tidal forces exerted by the large parent planet (and any additional satellites it might have). These geologically active large moons are likely to have their own magnetic fields, the same way earth does, and those would provide their surfaces with protection from the parent world's magnetic field and radiation belts.

A dense atmosphere also provides substantial protection from radiation, so exomoons with dense atmospheres might not be terribly bothered by the primary's radiation belts. Dense atmospheres might be a problem for moons close in to the parent star, but it would be a plus for worlds orbiting at some distance, allowing them to maintain liquid water and comfortable surface temperatures for life as we know it. It would also help them to moderate their climate, perhaps compensating for the long "day" on moons that orbit a great distance from their primary. Really dense atmospheres even refract light, giving you up to a couple of hours of extra daylight, again potentially serving to moderate the climate on some moons.

A really big gas giant (say, 5-10 times the mass of Jupiter) has an enormous gravity well, but we don't know if its magnetic field and radiation belts scale in the same proportion. It's possible you could have moons that orbit well outside of the radiation belts around such a large giant, but which still complete their orbits in a reasonable period of time (days, not months).

One other point - a large gas giant that's fairly close to its moon would put out a lot of heat, like a giant heatlamp in the sky. That would likely expand the habitable zone, the zone in which water could be expected to remain liquid.

Large gas giants could potentially host multiple habitable moons. And smaller ice giants - worlds the mass of Neptune, for example - could also host Mars or even earth-size moons. Neptune-mass worlds appear to be fairly common based on our current observations. If just a small percentage of them host moons that are the mass of terrestrial planets, that could add up to hundreds of millions of potentially-habitable exomoons circling around that class of planet alone.

Oh, and for small red dwarf stars, terrestrial planets in orbits close enough to support liquid water would soon find themselves tidally locked - one hemisphere would always face the parent star. Not pretty. That isn't an issue for exomoons. The primary might end up tidally locked, but the moons orbit the primary and would always have stable day/night cycles. They'd also potentially have the primary functioning as a big heat lamp at night, keeping the dark hemisphere from getting *too* cold during the long night. And the radiation belt around a gas giant orbiting such a small star is likely to be far less intense than the ones sported by the gas giants in this system. The red dwarf also throws off a lot less damaging UV radiation. We may find that the only habitable worlds around small red dwarf stars are exomoons - and there are a LOT of red dwarf stars. They vastly outnumber stars like our sun, by something like 10:1 I believe.

For years the assumption has been if there are large planets buzzing around the inner portion of a given solar system that such a system cannot be host to a habitable, terrestrial world. Clearly, that assumption is no longer valid. There are all kinds of plausible scenarios where moons could be perfectly habitable. I wouldn't be at all surprised if the number of habitable exomoons exceeds - indeed, greatly exceeds - the number of habitable exoplanets.

Re:Err, waitaminute.

[TapeCutter]

Life that evolves from planet with strong gravity would be massive and strong

More likely light weight and strong but I can see from the rest of your post you're not interested in heuristics based on what is more likely, it seems you would rather do a brute force search of the universe.

Re:Err, waitaminute.

[djowatts]

Indeed :/

Re:Err, waitaminute.

[IrquiM]

Erh... Water? It provides radiation shielding.

Re:Err, waitaminute.

[Anonymous Coward]

All of Jupiter's moons are constantly bathed in enormous amounts of radiation.

What's your point?

New bacteria found fueled by radiation

Re:Err, waitaminute.

[dasherjan]

I've always wondered if a moon had a magnetic field like the earth's. If that would be enough to shield it.

Re:Err, waitaminute.

[dpilot]

I remember hearing this, realizing that "Farmer in the Sky" wasn't even physically possible, not just politically, economically, socially, and technologically, and being disappointed.

Re:Err, waitaminute.

[Nox3173]

Um, wouldn't you actually increase bone mass and density in a developing organism in a high gravity environment, an effect similar to the opposite effect of the bone mass and density loss experienced by low gravity space flights?

Re:Err, waitaminute.

[GameboyRMH]

Clearly this is a secret message encrypted with some kind of curses-and-food cipher.

Re:Err, waitaminute.

[kalirion]

Life will find a way.

Re:Err, waitaminute.

[SBrach]

Just a big magnetic field which would make it really hard for any kind of civilisation to get pass bronze age.

Genuinely curious. Why?

Re:Err, waitaminute.

[jc42]

A really big gas giant (say, 5-10 times the mass of Jupiter) has an enormous gravity well, but we don't know if its magnetic field and radiation belts scale in the same proportion.

And the gas giants we have available would suggest that we not make guesses about magnetic-field strengths of gas giants until we have a lot more direct data. Jupiter's magnetic field is much stronger than Earth's; Saturn's is somewhat weaker. The mechanisms that produce these fields aren't understood very well. This gives a lot of latitude to science-fiction authors, but not much actual information about what might be out there in our real universe.

One thing we can probably safely predict is that any Earth-like satellite of a gas giant would probably have more tidal heating than Earth, giving it a warmer interior, and probably a stronger magnetic field than ours. But there's room for a lot of variation here, depending on distance from the primary and the age of the system. Just look at the variety in Jupiter's four planet-size satellites. Callisto's tidal heating seems to have a much smaller effect that Io's. So if we were to put Earth in Callisto's orbit, and move Jupiter to Earth's orbit, it wouldn't change much for our Earth. Well, except that that Earth would probably be tidally locked, giving it a day about 17 times longer than ours.

Re:Err, waitaminute.

[sunspot42]

Callisto has less tidal heating because it's much further out - about 2 million km if memory serves. I think Io is closer to 400,000km from Jupiter. Europa orbits not too much further out, at under 700,000km, then Ganymede at 1 million km. So Io is getting pushed and pulled on by tugs from Europa and Ganymede, not to mention Jupiter itself. Callisto in comparison experiences very weak tugs from Ganymede, and not much at all from Europa or Io. And Callisto experiences those tugs less often, since its orbital period is much longer. I think Calisto takes 17 days to complete an orbit, while Io zips around in well under 2.

Re:Err, waitaminute.

[TapeCutter]

Things with exoskeletons (the majority of critters) would be smaller, gravity is known to dictate their maximum size here on Earth. Things with internal skeletons might go the other way but are also ultimately limited by gravity. They may develop bird like bones to increase size while retaining strength and reducing mass or they may even develop bones that are made of something stronger and lighter than limestone.

Re:Err, waitaminute.

[That Guy From Mrktng]

Well obviously you have to apply some filter when you're looking for life in something as big and massive as the universe I get that. I wouldn't start the search from a brute force approach, but I'll try to keep the window as open as possible and not just discard exoplanets because they don't share $property that earth exhibits.

Anyway, ET life is cool and all, what happens if we confirm that 500 light years from earth theres life? (besides media, experts and marketing rage) seems like everybody actually believes that we are not alone, common sense yells when someone tries to point that the only living beings are those in earth, probabilities are to hight that even non-science-driven people get it. We should be focusing in actually getting there, brute force propulsion put us on the moon but is not going to help us to go outside our solar system.

This is good because

[florescent_beige]

Now we know the probability of life developing on a distant moon has gone up from .2a to .25a where a is an unknown value between 0 and 4

That's an exobiology arithmetic joke you cretins.

Re:This is good because

[geekoid]

so it's gone up significantly.

Re:This is good because

[Calos]

Only for significant values of a.

if a=1E-5, it's made no difference at all.

And then...

[errandum]

And then there is the (small) logistic problem of building a spaceship that could get there. As in, infinite fuel and traveling without a reasonable timeframe for a human being.

Re:And then...

[dudpixel]

And then there is the (small) logistic problem of building a spaceship that could get there. As in, infinite fuel and traveling without a reasonable timeframe for a human being.

This is not entirely correct.

Yes we (apparently) lack a way of getting there, or anywhere close for that matter.

The problem is that you suggested we need some sort of fuel (inferring a solid/liquid fuel like we use in spacecraft currently). The other problem is that of time.

If you solve the first problem, the second should become trivial. The "fuel" needs to be something that exists not just on earth. It must involve nullifying the effects of gravity.

I'm not sure if physics has reached a point where we can say whether or not this is even a possibility, but it has been suggested that Einstein thought it was possible.

Re:And then...

[dudpixel]

Let me also add that without any known way of getting there (and no solution in sight), I dont see the point of these studies.

Re:And then...

[black soap]

Maybe we'll find something so interesting, it will inspire us to go out and invent a way to get to it?

Re:And then...

[dudpixel]

but surely we already have enough motivation....although on second thoughts, you are probably correct in that it is the governments and the general populous that need to be convinced, rather than scientists and engineers. The governments (and by extension, the people) need to allocate funds and resources for such things to happen...fair enough.

Caveats:

[blair1q]

1. Insane tidal forces. The whole atmosphere getting thicker and thinner throughout each day. Oceans sloshing up and down by hundreds of meters in depth - not length, depth - twice a day along coastlines.

2. Insane temperature variances as the "moon" is eclipsed by the planet for a good portion of every "month". Whole oceans freezing over and thawing out every few thousand hours.

So, really, being at an earth-like distance from a sol-like star is bollocks for deciding whether there's life on such a rock.

Re:Caveats:

[Anonymous Coward]

Wouldn't this result in tidal locking and thus synchronous rotation, making everything stable once it's in effect?

Re:Caveats:

[SixAndFiftyThree]

1. The moon would be tidelocked, if it were close enough to have such huge tides, no question.

2. Depends on the orbital period; three of Jupiter's Galilean satellites have periods of a week or less, and a quick calculation based on the diameter of Jupiter versus the diameters of their orbits suggests that none of them is in total eclipse for more than a few hours ... better numbers here. Since I routinely survive a twelve-hour night with no ill effects, the eclipse seems to be a minor problem. A tidelocked planet would have a day equal to its month, though, which might be a problem if the month were more than two or three days, but a lot would depend on the presence of oceans, which are huge reservoirs of heat, and on wind patterns.

"Those who refuse to do arithmetic are doomed to talk bollocks."

Re:Caveats:

[Anonymous Coward]

Those are possible, but moons are also usually tidally locked, meaning no severe stresses. Jupiter's biggest moons have orbital periods on the order of a few days, so even with one side always facing the host planet, you could get an earth-like cycle. And half the moon wouldn't even see the daily eclipse, because it'd be night there anyway. With a thick enough atmosphere (which, if it's habitable in the first place, it'll have), the eclipse wouldn't freeze the oceans. There are plenty of ways to make a world uninhabitable, but simply being a moon isn't one of them.

Re:Caveats:

[Anonymous Coward]

I saw a documentary once where a number of furry natives had helped armed rebels overthrow an evil empire, and they lived in a scenario just like this one!

Re:Caveats:

[canajin56]

No to number 2. Yes to number 1, but it's not that bad. If you're as close as the "artist's rendition" drawings in the picture, where the gas giant is taking up half of the sky, then yeah, the tidal forces would be millions of times greater than the moons. But that's so absurdly close it doesn't bear thinking. If you take Saturn as a "typical" gas giant, and put a moon 400,000 KM away, then although the tidal forces would still be 10,000 times as great, the size in the sky of Saturn would only be 16 times as great as the Moon. That might cause more frequent eclipses, but they're not going to last much longer. Because at that distance the orbital period of our moon will be 24 hours. A worst-case eclipse would last for 30 minutes, and occur once per day. Depending on the specifics of the orbit, they might occur a whole lot less than that. (We don't get an eclipse every single month). But those tidal forces are still pretty awful. Except that at those forces, the moon would certainly be tidally locked. So although there would be severe stretching because of these forces, the pull would always be in the same direction due to the tidal locking. So there would actually be less severe tides than Earth has.

Re:Caveats:

[dryeo]

Tides would depend on whether there were other Satellites of significant size in a close orbit. Most of the major Satellites of Jupiter are heated by tidal effects even though tidally locked.

Re:Caveats:

[Intrepid imaginaut]

Oceans sloshing up and down by hundreds of meters in depth - not length, depth - twice a day along coastlines.

That would make for some awesome extreme surfing.

Re:Caveats:

[ResidentSourcerer]

Insane tides only while the moon tidally locks to the primary.

Also depends on the distance to the primary. While gravity goes down with the square, tidal forces go down with the cube of distance.

Re:Caveats:

[SixAndFiftyThree]

Good point indeed. Bear in mind that satellites in orbits very close to each other would be unstable: the orbits would change in a time much shorter than it would take life to evolve. IIRC the closest pair of Galilean satellites are in a 3:2 resonance ... lemme see ... actually 2:1 by http://en.wikipedia.org/wiki/Galilean_moons and their closest approach is 250,000 km, which makes for tides about four times as strong as on Earth (tidal force is inversely proportional to the cube of distance). With bigger satellites the tides would be stronger in proportion to their masses. OK, so a system with two Earth-sized satellites might have very big tides.

Re:Caveats:

[blair1q]

Okay. Tide locking. Now "night" is weeks long, and so is "day". No chance of forming a persistently temperate zone. The proper conditions for biochemistry would exist for a couple of hours every few weeks.

The bollocks are in your court.

Re:Caveats:

[blair1q]

But they had help. And the empire, while evil, was also stupid. Who brings two-footed walkers into a forest without they're the ones that can walk on logs?

Re:Caveats:

[blair1q]

"Life flourishes in our Arctic "

You're confusing "flourishes" for "developed".

The part about the planet acting as a heatlamp makes more sense though. It would be a huge moderator.

Re:Caveats:

[dryeo]

I'd think that any system with 2 Earth-sized satellites would have them spaced further apart or only one Earth-sized and the rest closer to moon-sized. Either way resulting in tides closer to what we experience.
Hopefully one day we'll have real examples.

Wonder how astronomy is...

[Anonymous Coward]

...developed on a moon. Would the fact they they revolve around a planet that revolves around a sun change the way their society develops? Would they have "planet gods" as well as "sun gods"?

Yeah, sure, there's a lot of interesting science about the development of the creatures in the first place, but I'm more interested in what their society and culture might be like.

Re:Wonder how astronomy is...

[MightyMartian]

Oh Mighty Pog of the Mismatched Testicles...

somebody has been reading

[mikerubin]

2063.....

Re:somebody has been reading

[Lanteran]

Huh, I make this mistake quite often as well.

The new find boosts prospects for life?!

[c0lo]

TFT

New Find Boosts Prospects For Life On Distant Moons

Thanks God!!! From now on (and because of that), those moons do have some chances to develop life...

Re:The new find boosts prospects for life?!

[florescent_beige]

Thanks God!!! From now on (and because of that), those moons do have some chances to develop life...

Only if the scientist who wrote that entered the sphere.

Re:The new find boosts prospects for life?!

[eyenot]

Thanks God!!! From now on (and because of that), those moons do have some chances to develop life...

Only if the scientist who wrote that entered the sphere.

Or if the formation of life is somehow dependent on observation (via Heisenberg "uncertainty"). In which case moons of this type in our observable universe would indeed have increased in their chance of producing life.

Re:The new find boosts prospects for life?!

[jc42]

Thanks God!!! From now on (and because of that), those moons do have some chances to develop life...

Only if the scientist who wrote that entered the sphere.

Or if the formation of life is somehow dependent on observation (via Heisenberg "uncertainty"). In which case moons of this type in our observable universe would indeed have increased in their chance of producing life.

Actually, you don't need Heisenberg's Uncertainty Principle; you just need some basic statistical knowledge.

A similar example from a few years back: There was a widely-echoed calculation by biologists that there was about a 50% probabability that there was a large mammal (for some definition of "large") that was still "unknown to science", i.e., not described in The Literature. Then in 1999 there was a printed report of new species of deer in Southeast Asia. When jounalists asked scientists if this meant that there were probably no new large mammals to be discovered, they were told that it actually increased the probable number of undocumented species.

The journalists were generally baffled by this. If you've found the last one, how does that mean that there are more? Where did they come from?

But, as anyone with a few basic statistics courses under their belt understood, the scientists were right. The 50% estimate was the probablility that there was one (or more) undocumented species, given the time series of recently-published new species descriptions. That series had been slowing down, and straightforward calculations predicted it would hit zero sometime in the next decade. But a new species changed the time series, and new calculations would take that into account. It moved the predicted zero crossing further into the future.

Back in the 1970s and 80s, there were a lot of jokes about a similar time-series calculation: If you looked at the time series of estimates of the size of the (dwarf) planet Pluto since its discovery in 1930, the prediction was that Pluto would disappear entirely sometime in the early 1990s. It didn't, of course, but that may have been due to the additional discovery that Pluto had somehow split into a pair of small planet(oid)s. This fissioning seems to have stopped the shrinkage, and Pluto is no longer predicted to disappear (except in the official list of planets).

There's a whole branch of statistics dealing with how you make good predictions based on the data that you have right now, and how you change your predictions as new data comes in. This is done a lot in research projects, to determine when they've collected enough data to say that it's not worthwhile to continue, because the numbers are significant enough to publish right now.

Death Stars are more of a worry

[Freaky Spook]

Personally, I would be much more worried about tidal forces. Though if it is far enough away from the gas giant...

I'd be more worried about Death Stars showing up and ruining my plans for rebellion. Hopefully they exit hyperspace on the far side of the gas giant giving me enough time to launch a counter assault......

Obligatory Star Wars reference

[gtarthur]

Forest moon of Endor, watch out for any strange "unfinished" artifacts...

Red Dwarf Stars

[satuon]

Moons orbiting a gas giant planet would also solve the tidal locking problem for red dwarf stars.

Re:Crazy Day-Night Cycle

[sunspot42]

What about the Day-Night cycle? Isn't going to be much more complex for a body that's orbiting a body that's orbiting a sun?

The day/night cycle would be the duration of the moon's orbit. Half would be day, half would be night, on any given point. It's not more complex, but it's likely to be longer. Life on earth doesn't seem to have an enormous problem with long days and nights - the arctic is quite biologically rich, in spite of the harsh climate (by human standards).

Re:More Flying Spagetti Monsters

[TapeCutter]

When I was a kid in the 60's, nobody had observational data that planets outside our solar system even existed, many of the moons and rings around the gas giants were unknown, and black holes were nothing more than a "mathematical curiosity".

Re:More Flying Spagetti Monsters

[JasoninKS]

Use to be we didn't have observational data for lots of things: germs, bacteria, radiation...shall we continue the list?

Re:Crazy Day-Night Cycle

[ByOhTek]

Incorrect, it would be the rotation around the axis, with a likely eclipse each orbit, but unless the orbit were *VERY* small, that eclipse wouldn't be more than an couple hours per few days.

The day/night cycle would be as long as the orbit only if the moon were tidally locked.

Re:Crazy Day-Night Cycle

[Nadaka]

Even if they are not tidally locked, the day night cycle will be the composition of its orbital period and rotational period. For small orbits, that could dramatically affect the duration of the day.

Re:Crazy Day-Night Cycle

[jellomizer]

Yes it would take longer for scientists to figure out that they are not in the center of the universe. Those cycles would take much more calculations to figure out that they are orbiting a planet that is orbiting the sun. Then when they point their telescopes towards Sol they figure there is no life there as there arn't any hot Gas Giant Planets close enough to the Sun. To create to support a moon that can keep life.

Re:Crazy Day-Night Cycle

[jc42]

Even if they are not tidally locked, ...

So is there any data on how likely this is? In our solar system, all seven of the planet-sized "moons" (Luna, Io, Europa, Ganymede, Callisto, Titan, Triton) are tidally locked to their primary. Also, in the Pluto/Charon pair, each is tidally locked to the other. So our system doesn't lead us to expect that many Earth-size satellites of a gas giant would have a day different from their orbit around their primary. I'm sure that some astrophysicists could calculate the probabilities, but I haven't read that anyone has done so.

Not that it would matter all that much to any life on such a "moon". On the side facing the primary, there would be a solar eclipse of a few hours every day, but that wouldn't materially affect the supply of sunlight. And this is assuming that the orbit is approximately parallel to the system's ecliptic. If the gas giant's satellites are in a highly-inclined orbital plane (as with Uranus), there would be only a few eclipses per year, similar to what we see. But we expect that Uranus is an anomaly, and the norm will be that most orbits in any (single-star) system will be close to coplanar.

There have been a number of science-fiction novels written that include such systems. Anyone have a favorite?

Re:Crazy Day-Night Cycle

[sunspot42]

Any moon that's approximately the mass of a terrestrial planet and which orbits a gas giant will eventually become tidally locked. In fact, it'll become tidally locked fairly quickly - within a few million years after formation or capture, based on the studies I've seen cited. That means its "day" will be the amount of time it takes to complete an orbit around the primary.

Re:Crazy Day-Night Cycle

[sunspot42]

I've read about studies which indicate such moons always become tidally locked - planets too, in close orbits about their star, according to simulations.

Based on what we currently know, I think it's safe to assume any terrestrial-mass exomoons orbiting exo gas giants or ice giants will be tidally locked to their primary. They'll likely also occupy resonance orbits with the other moons in their system, as we see with the Jovian moons (and possibly Saturn's moons, though I don't know as much about that system).

The length of any eclipses experienced by these moons would vary greatly depending on how close they orbit to the primary. For moons orbiting far out, I can't imagine the eclipses would have any significant impact on climate. Moons orbiting close in around enormous gas giants would experience longer eclipses, but they'd also have the big primary up in their sky functioning as an enormous heat lamp (it would also bathe the night side in a lot of reflected light). On the whole, worlds closer in would probably be warmer than worlds orbiting further out, in spite of the eclipses. Eclipses would last at most a couple of hours I should think - night could last for days.

I wonder if there are any particularly massive gas giants floating around out there with whole mini-solar systems orbiting them, including smaller gas giants, ice giants and terrestrial planets?