The Sounds Of Venus? Options

[Guest_Richard Trigaux_*]

Think something could be done with a DS2 type mass/volume budget?

Doug

The landers would have need a radio, solar panels, etc...

[4th rock from th...]

... Viking 2's seismometer could operate briefly in full waveform recording mode...

...Much the same could be done with the Apollo seismometer data: 3 Long-period axes and 1 vertical short period channel...

Hi Edstrick,

Is this data avaliable on the net? Some sort of ascii file?
If it is I can give it a try ;-)

[edstrick]

The Viking and Apollo data *MAY* be available on Planetary Data System geophysics or planetary science nodes. The Viking data was a pretty small volume because of data transmission limitations.

The Apollo data is much more extensive and has been extensively "worked" by a variety of international seismic research teams, I (think) that there have been a number of interesting papers by a (I think) Japanese reararch group who's used more advanced software and faster computers to find weak moonquakes in the data. After all, they are <if they can ever launch it> going to fly a lunar orbiter with 2 penetrators containing seismometers. They need experience working with lunar seismic data.

[Decepticon]

One sound I would love to hear is Europa's ice surface hev up and down.

Living in Ontario Canada during the winter most of the smaller lakes freeze over. When ice fishing you can sometimes hear the massive slabs of ice cracking and rubbing together. Very eerie sound.

Just imagine being part way threw its Ice crust and hearing this sound on a foreign moon.

[Guest_Richard Trigaux_*]

One sound I would love to hear is Europa's ice surface hev up and down.

Living in Ontario Canada during the winter most of the smaller lakes freeze over. When ice fishing you can sometimes hear the massive slabs of ice cracking and rubbing together. Very eerie sound.

Just imagine being part way threw its Ice crust and hearing this sound on a foreign moon.

This needs a high frequency seismometre on Europe.

[edstrick]

We do *NOT* know how well the Europa ice-crust is decoupled from the underlying rocky crust. Two things that have been massively ignored by press coverage of Europa are as follows:

1.) The geological activity patterns imply a thickening of the crust and declining activity patterns in each area. Thin-ice-pack breakup and rifting, followed by narrow cracking and/or hot-spot formation.

2.) Post Voyager models suggested that tidal heating in Europa may be inadequate to keep a steady state ocean liquid under a crust, but there may be cyclic heating and activity. The crust largely freezes, tidal energy loss is low, and the orbit builds up eccentricity under pumping from Io and Ganymede. That pushes up tidal heating rates till the crust starts to soften and you get runaway heating, massive melting, an outburst of activity, and the orbit rapidly circularizes, shutting off the heating and starting the next cycle as the crust freezes.

I think the geology is entirely consistent with such models. The one thing from Galileo that pretty much proves the crust isn't frozen down to rock is the magnetic field data that shows there's a conductive, probably brine layer, in the near-subsurface. Probably the crust concentrates salts and acids as it freezes till it can't freeze any deeper.

There's probably a lot of this in the technical planetary geology literature in the last decade that's totally below the horizon of press-release driven reporting which is most everything we see with few exceptions, like Bruce Moomaw's reporting.

[Guest_Richard Trigaux_*]

I think the geology is entirely consistent with such models.  The one thing from Galileo that pretty much proves the crust isn't frozen down to rock is the magnetic field data that shows there's a conductive, probably brine layer, in the near-subsurface.  Probably the crust concentrates salts and acids as it freezes till it can't freeze any deeper.

As a matter of facts when salty water freezes, it concentrate salt. And thus, the freezing point gets lower. So that an equilibrium is reached with a certain salt concentration.

But to have a cyclical activity, in your model, needs to have the water completelly frozen.

Perhaps Ganymede is more salty than Europe.

My idea about Europe is that the activity is rather due to accumulation of volcanic gasses from the rocky core. The gas dissolves in the water, until enough concentration is reached, and then the limnic eruption breaks the ice crust, lefting the blocks chaos which are observed in many places.

You speak of the decoupling of the ice crust from the rocky core. Two extreme cases are possible:
-The water is completelly frozen, we have an ice shield allowing eventual ice mountains to form
-there is a completely free water layer, and ice mountains cannot form

intermediary cases would be:

-the ice layer is free, but can be occasionally blocked by the summit of some rock mountains. In such case, the whole ice raft could break
-The ice layer is not free, but a thin water layer allows it to flow like a glacier.

The point of Decepticon was to hear the creaking of the ice crust, thinking that it floats on liquid water. To hear earthquakes in the underliying rock layer is another story, especially if there is a liquid layer. This is not impossible, this situation occurs on Earth, where seismic waves can travel through the liquid core, or through magma chambers. But I never heard of seismology through the ocean, frozen or not. There is a huge difference of density between water and rock, which makes the coupling low.

[edstrick]

A network of small penetrators with seismograph/geophones + magnetometers + heatflow sensors would be enormously valuable.

Ice-sounding radar has enormous potential at Europa, but from an entirely different radar methodology, so does radar interferometry. The sort of thing that takes dual radar images <as on the shuttle radar topography mission or with the european ERS-1 and 2 satellites flying nearly identical groundtracks> and generates an interferogram from the data. Interference fringes show down to millimeters of relative ground deformation with some 10 meters horizontal resolution. Europa's crust, whether grounded, partially free, or free-floating, *MUST* flex under orbital tidal flexing and should be visible in interferometry data. I know the studies have been done in the context of detailed geophysical models of Europa for what amplitude effects are expected, but I don't know the results of the studies.

There's more than one way to skin the Europan cat <catfish>, all of them well give different views on crustal thickness and dynamics and be of complementary value... too many to fly on single missions, especially limited ones like the pre- and post-Prometheus missions using chemical propulsion must be.

[Guest_Richard Trigaux_*]

A network of small penetrators with  seismograph/geophones + magnetometers + heatflow sensors would be enormously valuable.

Why not sonar sounding, or provoked explosions? As on Earth with seismometres, we should detect easily a liquid layer.

Such penetrators could be VERY small, just an arrow with a piezo detector and a radio. playback of interesting events would require little power, but it would also require a permanent satellite around Europa.

Ice-sounding radar has enormous potential at Europa, but from an entirely different radar methodology, so does radar interferometry.  The sort of thing that takes dual radar images <as on the shuttle radar topography mission or with the european ERS-1 and 2 satellites flying nearly identical groundtracks> and generates an interferogram from the data.  Interference fringes show down to millimeters of relative ground deformation with some 10 meters horizontal resolution.  Europa's crust, whether grounded, partially free, or free-floating, *MUST* flex under orbital tidal flexing and should be visible in interferometry data.

I noted tremendous images of volcanoes or seisms on Earth, with interferometry fringes showing deformations of only centimetres. We could see Europa "breathing" with tides. Perhaps active faults, if there are.

If there are points where the ice crust is linked to the rock core, these points should be very visible as lower deformation points surrounded with very active zones. A case I did not noted is that the crust would move relative to the rock, while touching it in some points, generating friction on these points. If this happens, or happened in past, we should find volcanoes or mountains with a flat summit (ice movement being the most efficient erosion mean).

[tty]

The point of Decepticon was to hear the creaking of the ice crust, thinking that it floats on liquid water. To hear earthquakes in the underliying rock layer is another story, especially if there is a liquid layer. This is not impossible, this situation occurs on Earth, where seismic waves can travel through the liquid core, or through magma chambers.  But I never heard of seismology through the ocean, frozen or not. There is a huge difference of density between water and rock, which makes the coupling low.

Seismology does work through the Earth's core which is liquid and the low-velocity layer that is partly melted. However note that S-waves don't propagate through a liquid but P-waves do, so an analysis of the waves received from a number of seismic events at known distances from a seismometer will yield a profile through Europa. A known azimut would also be valuable if there are local differences in the profile.
The problem with this is that it requires either a network of seismometers or impacts/explosions at known locations relative to the seismometer. Either way means a lot of weight to be moved to Europa.
The most cost-effective solution would probably be one seismometer and a number of small nuclear charges (which can weigh less than 100 lb each). However I imagine the political and ethical problems would be considerable.

tty

[Guest_Richard Trigaux_*]

The most cost-effective solution would probably be one seismometer and a number of small nuclear charges (which can weigh less than 100 lb each). However I imagine the political and ethical problems would be considerable. 
tty

useless: simply projecting some weights at high speed would produce the same effect, as on the Tempel comet.

As for the pollution, it is unacceptable on Earth, and, for weaker reason but still strong enough, also inacceptable on other planets. Remember that many expect that Europa may host life, and, until we have not found evidence of the countrary, for instance after drilling into its ocean, we should treat it as an inhabited world. Even lifeless, we cannot expect what we shall do -or even be- in millions of years, while the nuclear wastes will be still hot, perhaps we shall have some need of Europa. With my opinion having engaged Earh in millions of years of storing and monitoring nuclear wastes was at least not good management, but this is off topic on this forum... and in too many places elsewhere.

Anyway your idea (one seismometre, several explosions) seems fine, and it could be done with one lander, and later a rocket sending a well timed string of bullets.