Which of Saturn's moons have an atmosphere

Sporally · #1 (**permalink**) 26-February-2006, 10:32 AM

The title says it all. Which of Saturn's moons have an atmosphere? I personally like moons with atmospheres the most. But i haven't found a site that states which of the moons that has an atmosphere. I know Titan has, but those rocks around Saturn surely hasn't got an atmosphere. Thx in advance for your help.

the_bullet · #2 (**permalink**) 26-February-2006, 11:00 AM

I think before Cassini only Titan was thought to have an atmosphere. But I believe Cassini found Enceladus to have an atmosphere also.

Sporally · #3 (**permalink**) 26-February-2006, 11:29 AM

Really, i thought there were more moons. But nice to know Cassini has done a difference here.

antoniseb · #4 (**permalink**) 26-February-2006, 12:09 PM

It really depends on what you call an atmosphere. Enceladus' atmosphere is most-likely pretty short lived. Gasses ejected from its geysers near the South Pole are around the moon, and rapidly evaporating away. It is likely that this moon and many others have ultra thin atmospheres of Xenon and other vapors coming from the surface, and not escaping easily.

I think your question would be better if reworded to ask which moons have atmospheres denser than some particular level, say one millibar. Then the answer is "only Titan".

Sporally · #5 (**permalink**) 26-February-2006, 01:44 PM

OK, that's a point. So, atmospheres that is not just temporarily - what moons do we have in the entire solar system of that kind?

Titan
Charon
Io???

I guess we have a small handful of moons around Jupiter, Uranus and Neptune, but i don't know much about them. I only know a couple of names, but not sure i can say anything about them, might even have great problems placing them by their rightful owner planet

The moons i like the most are those with a static atmosphere. I see the other moons as rocks more or less (sorry for my ignorance. I still want to explore them, but my priority has always been those with static atmospheres).

And i have anyother question i just thought of this morning:

All planets (with the exception of Pluto) beyond Jupiter are gasplanets. One thing i don't understand is why only the planets are made of gas while the moons are solid. Actually i would have considered it to be the total opporsite since i know a great pressure makes things more solid while low pressure makes it harder to keep the molecules static (more or less). I see the point of low pressure and high pressure, but i don't see why e.g. Titan is solid and Saturn is not.

Kullat Nunu · #6 (**permalink**) 26-February-2006, 04:46 PM

* Titan of course has a dense atmosphere.
* Triton has a thin nitrogen atmosphere. However, is dense enoug to be visible. Even some clouds have been seen there.
* Io has a very thin sulphur atmosphere due to volcanic activity.
* Europa, Ganymede and Callisto (?) have extremely thin oxygen atmosphere created by micrometeors striking on surface ice.
* Enceladus has the transient atmosphere already described.

The atmospheres of the Galilean satellites are actually quite good vacuums.

Charon does not have measurable atmosphere. If it had, it should have been detected during the recent stellar occultation.

Beowolf · #7 (**permalink**) 26-February-2006, 05:35 PM

Quote:

Originally Posted by Sporally

And i have anyother question i just thought of this morning:

All planets (with the exception of Pluto) beyond Jupiter are gasplanets. One thing i don't understand is why only the planets are made of gas while the moons are solid. Actually i would have considered it to be the total opporsite since i know a great pressure makes things more solid while low pressure makes it harder to keep the molecules static (more or less). I see the point of low pressure and high pressure, but i don't see why e.g. Titan is solid and Saturn is not.

I think it's due to gravity. The gas-giants gravity is strong enough to hold onto the lighter elements like hydrogen and helium. The satellites on the other hand have much weaker gravity and would have lost the lighter elements to space over time. Still they are made up of a higher porpotion of lighter elements than planets and moons in the inner solar system.

Sporally · #8 (**permalink**) 28-February-2006, 12:24 PM

@ Kullat Nunu

Maybe the oxygen on Callisto and Ganymede is from microbes

But i see the point of impacts from meteors, guess there is no life on the icy surface of Europe and if the amount of oxygen is close to the same as Europe i guess that explains it, but it could be life - ok, i don't know much about those two moons molecules so maybe i'm entirely wrong.

@ Beowolf
That makes sence, but then i have to add i don't see the point that Saturn does not have a core greater than any of its moons. I've always heard of Saturn to be pure (or almost pure) gasses, but with greater gravity to pull the astroids towards it, it should have solid ground (not to mention the pressure that transforms many gasses into solid.

What about atmospheres around the moons of Uranus and Neptune? Did you mention those too (as said i don't know much about the moons out there except that i know there are many of them).

Kullat Nunu · #9 (**permalink**) 28-February-2006, 12:48 PM

It is a safe to say that the surfaces of all Galilean moons are lifeless. Extreme coldness combined with hostile radiation and vacuum is not the best place for microbes. The trace amounts of oxygen around these moons (I'm not even sure if the "atmospheres" are thick enough to be called such) are generated by micrometeor impacts, which release water molecules from surface ice. Then ultraviolet radiation breaks these molecules apart. Lighter hydrogen atoms escape easily, but heavier oxygen atoms stay behind. Or so I have understood it.

What comes to subsurface conditions, is completely different matter. It is very possible that Europe has a vast subsurface ocean (but remember, it has not been proved!) Callisto has probably colder, salty ocean, and quite possibly Ganymede too. Europa has plenty of internal energy generated by tidal forces, which could provide the necessary energy for lifeforms to evolve. However, it is very unlikely that multicellular life has formed there.

----

Saturn probably has a solid core, which is larger than many times more massive than Earth. Most of the planet is not gas, but liquid due to high pressure. Some of the hydrogen is in the form strange liquid called "metallic hydrogen", which acts like a metal.

----

Yeah, Triton, which is Neptune's largest satellite, has a visible atmosphere and even geological activity in the form of geysirs.

No atmospheres are found around Uranus' moons which is not surprising given the smaller size of the moons. Innermost and smallest of the large satellites, Miranda, has evidence of past geological activity. Its "coronae" formations resemble the active "tiger strips" on Enceladus. Miranda is only slightly smaller than Enceladus, so it is possible that the moon had similar transient atmosphere as Enceladus has before its activity ceased.

Sporally · #10 (**permalink**) 28-February-2006, 01:01 PM

At NASA they are afraid that microbes made it to Mars through both vacuum and extreme radiation and temperatures. So with a tiny atmosphere they could make a living of something (e.g. oxygen if they need this, if not, this is something they could evolve from). Of course the chance of life is with a very restricted evolution opportunity. Still surpriced of how those extreme microbes could survive in vacuum for such a long time. But taken into consideration that they might have succeded the travel they should have a chance on moons with tiny atmospheres.

Kullat Nunu · #11 (**permalink**) 28-February-2006, 01:49 PM

Every known living organism, extremophile or not, needs liquid water to live. Some microbes may survive high radiation in vacuum for a long time, but they're dormant. No microbe can be active on the surface of these moons or even on the surface of Mars, but if they manage to dig deep enough and find liquid water...

BTW, lack of oxygen is not a problem. In fact, oxygen is toxic to all lifeforms on Earth. Some, including us, have found a method to make use of it, but it still destroys our tissues causing aging.

Sporally · #12 (**permalink**) 28-February-2006, 02:21 PM

What i meant about the oxygen was that the microbes could produce it. But you might be right that microbes can't survive under these circumstances for long. This might be far out, but could the microbes live beneath the surface from a meteor impact and now producing the oxygen we see today - the oxygen is lighter than the solid stuff on the moon and therefore it reaches the surface of the moon. Don't worry, i believe in your theory that the oxygen comes from meteors, i just want to pursuit a theory about life on some of the moons

Kullat Nunu · #13 (**permalink**) 28-February-2006, 02:56 PM

I was unclear. The detected oxygen does not come from meteors, but from the surfaces of the moons instead. Remember, surfaces of these moons (except for Io) are icy.

Atmosphere composed of oxygen is not terribly good sign of life. But if we discover an Earthlike planet with ozone in its atmosphere (meaning there is oxygen) and methane we can be certain that something very interesting is happening there. Methane doesn't survive for long in an oxygen atmosphere, so something must replenish it. On Earth, that something is life. Some methane is produced by volcanism, though. On Mars, the methane detected is likely generated by geological processes where certain compounds from rocks react with water. Or from volcanism, meaning the planet is not dead. And, if the least likely and the most profound possibility is true, there's living organisms under the surface of Mars.

Sporally · #14 (**permalink**) 01-March-2006, 10:36 AM

OK, i misunderstood you. Thought you meant the oxygen came from the meteors. So i guess we haven't found any oxygen on Titan? I think i've heard that scientists believe in, i think it was nitrogen, as a possible replacement for oxygen. By this i mean they think nitrogen could be the source life elsewhere in the universe would use as their 'air'.

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