Starship Asterisk*

• Science 344(6179) 78 (04 Apr 2014) DOI: 10.1126/science.1250551

http://en.wikipedia.org/wiki/Enceladus wrote:

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<<Model of the interior of Enceladus from 2006.

The inner, silicate core is represented in brown, whereas the outer, water-ice-rich mantle is represented in white.

The yellow and red colors in the mantle and core respectively represent a proposed diaper diapir under the south pole.>>

neufer wrote:

http://en.wikipedia.org/wiki/Enceladus wrote:

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<<Model of the interior of Enceladus from 2006.

The inner, silicate core is represented in brown, whereas the outer, water-ice-rich mantle is represented in white.

The yellow and red colors in the mantle and core respectively represent a proposed diaper diapir under the south pole.>>

BDanielMayfield wrote:
Which view is right? I guess it Depends.

neufer wrote:

BDanielMayfield wrote:
Which view is right? I guess it Depends.

And are the geysers always around the South Pole or is there incontinental drift?

Nitpicker wrote:Seems to me like there is little evidence to support one kind of structure over the other (diapir or a "sandwiched ocean"). There is evidence of southern geysers forming the E-ring, but that doesn't really tell us anything about the geological structure creating the geysers. I might have been less likely to recoil from the "sandwiched ocean" idea, if the image was not described as a cartoon, and south was not drawn at the bottom, making it look like a low point for water to drain.

APOD Robot wrote:Most recently, an analysis of slight gravity deviations has given an independent indication of underground oceans.

So how do astronomers map the interior of a moon using only an orbiting spacecraft?

It all comes down to the subtle effect of gravity. We tend to think of the force of gravity on any planet as a constant. But in reality it varies depending on your global location and the composition of the planet under your feet. For example, Earth’s gravity measured at our equator is 9.788 m/sec2, whereas at one of the poles it may be as high as 9.838 m/sec2 (a difference of 0.5%).

“Gravity allows us to open a window into the interior of the moon,” said Iess. During three close flybys of Enceladus, Cassini measured variations in how the moon’s gravity pulled on the spacecraft. These variations revealed the large-scale characteristics of the moon’s surface and interior, including any mass anomalies — spots where there is an excess or lack of mass — typically due to a bulge or a basin, or even just a change in density.

While flying past Enceladus’s south pole, Cassini spotted a negative mass anomaly, likely due to a depression in the icy surface.

“When you look at the actual surface you see that, although there is indeed a depression, it is much larger than that needed to explain the gravity,” said coauthor David Stevenson (Caltech). In other words, there simply isn’t enough mass at the surface of the south pole to account for the gravitational field present there. So there has to be something more massive underneath the surface. “A natural way to do this is to have a layer of water, because water is more dense than ice.”

Nitpicker wrote:I didn't say it had no evidence. I said there is little evidence to support one kind of structure over the other.

DavidLeodis wrote:
The image was brought up through the "Pictured above" link where in its caption it stated the image was "a full-disk view of the anti-Saturn hemisphere on Enceladus". I take the "anti-Saturn" to mean the image shows a side of Enceladus that is not facing Saturn but does it also mean that side never shows its face to Saturn (like the far side of our Moon never faces the Earth).

neufer wrote:

DavidLeodis wrote:
The image was brought up through the "Pictured above" link where in its caption it stated the image was "a full-disk view of the anti-Saturn hemisphere on Enceladus". I take the "anti-Saturn" to mean the image shows a side of Enceladus that is not facing Saturn but does it also mean that side never shows its face to Saturn (like the far side of our Moon never faces the Earth).

Yes,

Art Neuendorffer ("anti-Satur(atfordia)n"