Lakes in the limelight, the 2013 image bonanza continues Options

[titanicrivers]

Juramike (Mike Malaska) has a new article in Icarus on the possibility of Nitrogen bubbles affecting large patches of the N polar seas as seasonal changes occur. A great image of the N polar region and a summary of the article are found on the Cassini website https://saturn.jpl.nasa.gov/news/3008/exper...-with-nitrogen/

[Ian R]

2017-03-20 Titan — A Double Take


2017-03-21 — Cassini Snaps Zero-Phase Titan

[TheAnt]

The features that appeared then to disappeared in liquid on Titan have indeed turned out to be foamy bubbles.
This finding is described in a paper in Nature and a popularized treat on the subject is found in Universe today.

[nprev]

Much of this work was done by UMSF moderator Juramike, who is quoted extensively in the Universe Today article.

[JRehling]

This fizzy seas result is one of the most science-fiction-like things I've read in planetary science. It's like something out of a comic book. Congratulations, Mike.

[rlorenz]

The features that appeared then to disappeared in liquid on Titan have indeed turned out to be foamy bubbles.

No they have not. The study (to which I also contributed) showed that nitrogen bubbles could be formed in certain circumstances. Such bubbles
could account for some transient phenomena observed on Titan's seas (aka 'the magic island' observed in radar) but they
cannot account for all the transient features observed (notably by VIMS, which only sees the top fraction of a millimeter of
material).

A more parsimonious theory is that surface roughness (either locally wind-driven, i.e. 'catspaw', or nonlocally - i.e. wind-driven
currents) explains all the observed transients.

Bubbles are still fun to think about, though.

[Juramike]

Yeah. A funny thing happened on the way to the Universe Today article....

About a month ago we had a press release that presented our Icarus paper on experiments to figure how much nitrogen goes into lake fluids. Lotsa fun implications. Lakes "breathing" in and out, gas release from liquid mixing, cool stuff (!). And we stated pretty much "Oh yeah, and bubbles might possibly could be an explanation for observations of Magic Islands in Titan seas." I mean, sure, it's still on the list of possible suspects.

A month later, another paper comes out in Nature Astronomy that describes model calculations (not using our new lab data, I might add) that had a press release saying that the problem was solved.

And somehow in a funky twist, the Universe Today article combined the Nature Astronomy article's press release first paragraphs with the last paragraphs of our earlier press release.

So basically, we got an extra bonus 15 minutes of fame riding on the back of a later paper that came to some of the same conclusions that we'd already published earlier.

I'm really not quite too sure what to make of all this....

But as for the observed Magic Islands in the lakes, I agree with Ralph that wind is a good (and leading) suspect for Magic Islands. But the properties of Titan lakes definitely causes some funkiness. (As in, no freezing of methane on Titan - but that's not a new discovery, our lab experiments just help with the "why".)

[ngunn]

I have a question about the way patches of bubbles might produce RADAR reflections. Please excuse me if the answer is already in one of the papers: I don't have access. Are we talking about bubbles distributed through the body of the liquid or a raft of some sort of scum accumulating on the surface?

[Webscientist]

Thanks Ralph and Mike for your courageous experimental study about the bubble phenomenon. Risky I guess with all these volatile hydrocarbons...
In Ligeia Mare, I note that the coastline near the "Magic Island" is particularly irregular with numerous peninsulas or bays.
I can imagine strong erosional processes in that area as well as potential disturbances in streams.

[rlorenz]

I have a question about the way patches of bubbles might produce RADAR reflections. Please excuse me if the answer is already in one of the papers: I don't have access. Are we talking about bubbles distributed through the body of the liquid or a raft of some sort of scum accumulating on the surface?

These are quite distinct hypotheses. Floating material (e.g. pumice rafts, or some sort of bubble foam) could explain both radar and near-IR brightness, as could surface roughness from wind or currents.

A bubble plume, with voids in the methane column, could give radar backscatter, but not near-IR.

A bubble plume would be expected to be anchored to the seafloor somehow ; floating material would be pushed around a lot by wind, so the magic island's recurrence at one spot might argue somewhat against it, although some sort of pumice analog continuously/episodically released from a seafloor volcano would have some preference for location, I guess.

[Juramike]

No, a bubble plume due to compositional mixing would not be anchored to the lake floor. It would be present anywhere there was a lower layer of ethane-richer fluid overlain by methane richer-fluid. It could be anywhere. And if there was a "bubble event" it could migrate around as the different portions of the lake hit compositional equilibrium at different times. It'd be really fun and exciting to watch.

There could, however, be places more prone to compositional mixing. Places where local winds are more prone to stir up the lakes fluids, cause mixing, and then generate a bubble-splosion. This could explain Magic Islands reappearing at same location (after a recharge of compositional disequilibrium.)

(Please note that Occam is starting to have a 5-o'clock shadow at this point....)

[ngunn]

Thanks for the informative replies.

Floating material (e.g. pumice rafts, or some sort of bubble foam) could explain both radar and near-IR brightness, as could surface roughness from wind or currents.
A bubble plume, with voids in the methane column, could give radar backscatter, but not near-IR.

Do we have any near-IR evidence either way for the original 'magic island'? If so I missed it.

No, a bubble plume due to compositional mixing would not be anchored to the lake floor.

So it seems to me we have two separate questions to answer regarding any bubble-related explanation for the transient features. What mechanism generates the bubbles, and in which way are they rendered visible?

Mike, I wonder if you have any ideas on surfactant materials that might plausibly be present in Titan's seas? Perhaps this is another area where experimentation could prove fruitful. Can you produce a long-lasting foam under Titan conditions?

[stevesliva]

I find myself wondering whether gravels entrained by a dense river would end up floating on top of a less-dense sea.

[rlorenz]

(Please note that Occam is starting to have a 5-o'clock shadow at this point....)

LOL! Quite. Note that I did say 'expected' to be anchored..... as you say, anything is "possible"

[Juramike]

So it seems to me we have two separate questions to answer regarding any bubble-related explanation for the transient features. What mechanism generates the bubbles, and in which way are they rendered visible?

Mike, I wonder if you have any ideas on surfactant materials that might plausibly be present in Titan's seas? Perhaps this is another area where experimentation could prove fruitful. Can you produce a long-lasting foam under Titan conditions?

Two ways you can make bubbles.
1) Heat up Titan liquids. Solubility of nitrogen in methane really drops off on heating.

2) Compositional mixing. Mix a liquid containing lotsa methane/nitrogen with liquid containing ethane (which doesn't like nitrogen so much). The excess will come out.


As for surfactants, methane (and ethane but less so) is a lousy solvent. So any surfactants that could dissolve to an appreciable and useful extent is a very short list. In our experiments we get a huge amount of bubbles generated. So all our calculations were assuming instant N2 release and bubbles and we didn't worry about long-lasting foams.