[X] My Assistant

[SigurRosFan]

Interesting news:

- Mysterious signal hints at subsurface ocean on Titan

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The tentative detection of low frequency radio waves on Saturn's icy moon, Titan, could signal an underground ocean of liquid water, a new study [led by Fernando Simoes] says.
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[remcook]

There's a paper in press at Icarus which also deals with the same data (Icarus in press bit doesn't seem to work now, so I can't give a link yet):

A Schumann-like resonance on Titan driven by Saturn’s magnetosphere possibly
revealed by the Huygens Probe
C. Béghin a,*, F. Simões b, V. Krasnoselskikh a, K. Schwingenschuh c, J.J. Berthelier b, B. Besser c,
C. Bettanini d, R. Grard e, M. Hamelin b, J.J. López-Moreno f, G.J. Molina-Cuberos g,
and T. Tokano h

they conclude that (from the abstract):

[...]
Extremely-low frequency waves generated in the ionosphere of Titan,
driven by the corotating Saturn’s frozen plasma flow, are assumed to be the most likely source for
the observation of the second eigenmode of a Schumann-like resonance at around 36 Hz in the
moon-ionosphere cavity. This particular mode is thought to be enhanced with respect to other
harmonics because of the particular location of the landing site with respect to that of the supposed
sources. The power budget of the observed wave amplitude seems to be consistent with a rough
model of the global current of the wake-ionosphere circuit.
[...]

Though I don't have a good idea about what that all means, it seems that it may be consistent with some sort of ionosphere interaction. In the conclusions they state however:

We cannot firmly conclude yet that only one scenario
can explain the ELF and “36 Hz” line seen in the PWA data,

Instead of a subsurface layer they think aerosols might be responsible for the reflection, as far as I can tell,

Within the low conductivity cavity which is thought to be deepened
by a high concentration of electrophylic aerosols, between the bottom of the regular ionosphere
and the “Huygens” conductivity layer, the emerging 36 Hz wavelets are assumed to be reflected
upwards. Then, the horizontal electric component of those waves may be subsequently enlarged, as
seen on the “36 Hz” between 105 and 70 km.

Note that F. Simoes is 2nd author here, so the sub-surface sea might well be an improvement on this work.

[remcook]

I also had a quick look at the PSS paper by Simoes quoted at the bottom of that article, but that only briefly mentions a sub-surface ocean (not in the abstract though).

It ends with:

Was the Schumann resonance really observed during the descent of the Huygens Probe upon Titan? Possibly, but the question is not entirely closed.

I find it very hard to decypher these papers, but it seems the Schumann resonance is caused by a highly conductive layer, which would possibly a sub-surface ocean. Anyone knows what they're actually talking about??

But I guess if they did find evidence for such a thing they would have submitted it to nature or science...

[TheChemist]

I struggled myself quite a bit too.
From what I understand, and awaiting opinions from people more familiar with Titan's atmospheric phenomena :

1. There is a curious signal detected by Huygens' PWA at 36 Hz.
2. First, it has to be made sure it is not an artefact (Icarus paper).
3. If it is natural, a source must be found for the electromagnetic disturbance causing the low frequency atnospheric wave (Icarus paper).
4. If the source is found, and if the 36 Hz signal is due to a Schumman resonance, then one way of explaining it is a reflection from the solid/liquid boundary of a subsurface ocean, according to the modelling in the PSS paper.

The Icarus paper link is http://dx.doi.org/10.1016/j.icarus.2007.04.005

P.S. This whole thing might pose interesting dilemmas to certain forum members who like Titan but trash Europa

[David]

If there's a Xanadu on Titan, then obviously its rivers must flow down to a sunless sea.

[Littlebit]

There is an overview here:

http://saturn.jpl.nasa.gov/news/features/f...re20070601c.cfm

But perhaps the biggest mystery is what generated the ELF wave in the first place. On Earth, they are initiated by lightning strikes that make electrons in the atmosphere oscillate, releasing the ELF waves.

The PWA was designed to search for ELF waves on Titan while a microphone on Huygens kept an ear out for thunder - a sure sign of lightning. Cassini has also been watching for lightning using its cameras.

However, Huygens suggests that there is no lightning, or very little. "If there is lightning on Titan, it is significantly less than the amount of lightning that Earth experiences," says Simões. So what generated Titan's ELF? No one is quite sure yet. "It might be generated by an interaction with Saturn's magnetosphere or related to Titan's intrinsic fields," suggests Simões. "Titan is proving to be an intriguing environment."

To say the least.

[mchan]

If there's a Xanadu on Titan, then obviously its rivers must flow down to a sunless sea.

Heh-heh-heh. Good one.

[Stu]

Sorry, but everytime Xanadu comes up I have horrible flashbacks to that dreadful film with Olivia Newton John and Jean Kelly...

[ngunn]

The possibility of underground lakes of methane/ethane in the upper regions of Titan's icy crust was discussed in an earlier thread relating to the very low density/porosity/possibly cavernous nature inferred from radar measurements for parts of Xanadu. The layer of water/ammonia invoked to contain this possible ELF resonance would on the other hand be located at the bottom of the icy crust, where conditions are presumably a bit warmer. So it's possible that Titan actually posesses two different kinds of sunless sea, one at the bottom of the Alph and one at the bottom of the ELF.