APOD: Ice Moon Tethys from Saturn Orbit... (2009 Dec 08)

[APOD Robot]

Ice Moon Tethys from Saturn Orbiting Cassini

Explanation: What processes formed the unusual surface of Saturn's moon Tethys? To help find out, NASA sent the robotic Cassini spacecraft right past the enigmatic ice moon in 2005. Pictured above is one of the highest resolution images of an entire face of Tethys yet created. The pervasive white color of Tethys is thought to be created by fresh ice particles continually falling onto the moon from Saturn's diffuse E-ring -- particles expelled by Saturn's moon Enceladus. Some of the the unusual cratering patterns on Tethys remain less well understood, however. Close inspection of the above image of Tethys' south pole will reveal a great rift running diagonally down from the middle: Ithaca Chasma. A leading theory for the creation of this great canyon is anchored in the tremendous moon-wide surface cracking that likely occurred when Tethys' internal oceans froze. If so, Tethys may once have harbored internal oceans, possibly similar to the underground oceans some hypothesize to exist under the surface of Enceladus today. Might ancient life be frozen down there?

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[orin stepanek]

Tethys; You're one big snowball. 8)

Orin

[neufer]

Code: Select all

Name       Diameter(km) 	Mass(kg)    Orbital radius (km)    Period (days)
-------------------------------------------------------------------------------
Enceladus   	500   	  1.1×10^20         	  238,000     	1.4
Tethys        1060        6.2×10^20              295,000     	1.9

• Oh the weather outside is frightful,
  But the fire is so delightful,
  And since we've no place to go,
  Let It Snow! Let It Snow! Let It Snow!

<<In Greek mythology, Tethys (Greek Τηθύς), daughter of Uranus and Gaia was an archaic Titaness and aquatic sea goddess, invoked in classical Greek poetry but no longer venerated in cult. Tethys was both sister and wife of Oceanus. She was mother of the chief rivers of the world known to the Greeks, such as the Nile, the Alpheus, the Maeander, and about three thousand daughters called the Oceanids. Considered as an embodiment of the waters of the world she also may be seen as a counterpart of Thalassa, the embodiment of the sea.

Burkert sees in the name a transformation of Akkadian tiamtu or tâmtu, "the sea," which is recognizable in Tiamat. Alternatively, her name may simply mean "old woman"; certainly it bears some similarity to ἡ τήθη, meaning "grandmother," and she is often portrayed as being extremely ancient.

One of the few representations of Tethys that is identified securely by an accompanying inscription is the Late Antique (fourth century CE) mosaic from the flooring of a thermae at Antioch, now at the Harvard Business School in Boston, Massachussetts. Tethys—surrounded by fishes—is rising, bare-shouldered from the waters. Against her shoulder rests a golden ship's rudder.

During the war against the Titans, Tethys raised Hera as her god-child. Hera, was not pleased with the placement of Ursa Major and Ursa Minor, so she asked Tethys, to help. Tethys, a marine goddess, caused the constellations forever to circle the sky and never drop below the horizon, hence explaining why they are circumpolar.>>

[Storm_norm]

Some of the the unusual cratering patterns on Tethys remain less well understood, however.

is it me, or could this be written better?

[Chris Peterson]

Some of the the unusual cratering patterns on Tethys remain less well understood, however.

is it me, or could this be written better?

There's not much that couldn't be written better. But I think that sentence is pretty clear.

[geckzilla]

I'm afraid of getting too off topic but Art's barely-on-topic post has inspired me to also be barely-on-topic.
Nano-snowman!

http://www.physorg.com/news179153163.html

From now on I'm going to associate Tethys with snowmen.

[neufer]

I'm afraid of getting too off topic but Art's barely-on-topic post has inspired me to also be barely-on-topic.
Nano-snowman!

From now on I'm going to associate Tethys with snowmen.

The world's smallest snowman measures 0.01 mm across, with a nose just 0.001 mm wide.
The snowman is mounted on a silicon cantilever from an atomic force microscope, whose
sharp tip is used to feel surfaces in order to create topographic surveys at very small scales.

While Cox's snowman holds the record for the smallest, MyFox News notes that the tallest snowman record is still held by the town of Bethel, Maine. Residents of the town built a snowman with a towering height of 34.62 meters, on February 17, 1999.
[about a billion times larger than above]

[orin stepanek]

Might be an endless supply for snow cones!

Orin

[neufer]

[about a billion times larger than above]

Correction: [about a million times larger than above]

[orin stepanek]

I wonder how many snowballs such as Tethys exist in orbit around the sun and between stars! Could it be that some time they could become an important source of water and fuel for spacefarers exploring the galaxy. Ahhh: just daydreaming again. I'm content to let APOD do the exploration of space for me.

Orin

[apodman]

Tethys photo - enhanced.

[Horombo]

in looking at the amazing image of Tethys something unusual jumps out in the center of the moon. It is an almost perfectly symmetrical “tombstone-shaped” pentagon right on the moon’s equator and just to the right of Ithaca Chasma. Is this an artifact of imaging or something more? Nature doesn’t produce that many straight lines, especially those that connect, and certainly not on this scale. Does anyone else see this? Ideas?

[neufer]

in looking at the amazing image of Tethys something unusual jumps out in the center of the moon. It is an almost perfectly symmetrical “tombstone-shaped” pentagon right on the moon’s equator and just to the right of Ithaca Chasma. Is this an artifact of imaging or something more? Nature doesn’t produce that many straight lines, especially those that connect, and certainly not on this scale. Does anyone else see this? Ideas?

The origin of polygonal impact craters - Evidence from Argyre region, Mars.

T. Ohman (Department of Geosciences, Division of Geology, University of Oulu, Finland), M. Aittola, V.-P. Kostama, M. Hyvarinen, J. Raitala (Department of Physical Sciences, Division of Astronomy, Uiversity of Oulu, Finland)

<<Polygonal impact craters are a ubiquitous feature on the surfaces of various bodies throughout the Solar System (Ohman et al., 2005). The currently favoured acoustic fluidisation model of impact crater's modification (collapse) stage requires that the rim material is nearly strengthless during the collapse, and thus can not have a ``memory" of the pre-existing crustal structures. In the view of polygonal crater data, this is not the case. Therefore, at least a slight adjustment is required to the current cratering models for them to correctly depict nature.>>

Iapetus, third largest moon of Saturn, has a massive hexagon shape, and the infamous ridge (JPL)


In this notated image of Phobos, we can see some of the hexagonal shapes on the moon's surface.

The Characteristics of Polygonal Impact Craters on Venus
Marko Aittola1 Contact Information, Teemu Öhman1, 2, Johannes J. Leitner3 and Jouko Raitala1

<<Polygonal impact craters (PICs) are craters whose shape in plan view is more or less angular instead of being circular or ellipsoidal. This type of craters are present and often common on the Moon, Mercury, Mars and several asteroids and icy moons. This survey proves that there are polygonal impact craters on Venus and they may provide a good tool to analyse the properties of the planet’s surface/crust/lithosphere as well as the impact process itself. This study also collaborates our previous results, that PICs are not an anomaly among craters, but an integral part of all impact craters regardless of their size or environment. Our study shows that there are regions where the straight segments of the crater rims most clearly follow the orientations of the dominant tectonic features of the area. Thus, the orientations of crater walls reflect–at least in some places–the local tectonics and zones of weakness also on Venus and could thus tell us about the directions and distributions of fractures or other zones of weakness in the crust.>>

[bystander]

http://apod.nasa.gov/apod/image/0912/tethys4_cassini_big.jpg

tethys_hex.JPG (8.45 KiB) Viewed 5858 times

If you are talking about this, it actually appears to be more hexagonal.

[msvenn]

Hello,

I was adviced to refer here on this matter, so..
Would any of you happen to know what this white spot is in the image?

http://cs.helsinki.fi/u/svenn/tethys4_cassini_big.tif
The second image is large (7,3MB) and in tif format in order preserve the image quality.

The original message:


Hello,

I was just browsing through the Astronomy Picture of the day archive and noticed something while zooming through the image: "Ice Moon Tethys from Saturn Orbiting Cassini" - 2009 December 08.

Close to "equator level" of the moon there's an anomality in pixel color levels compared to the surrounding image area. I added a red arrow to indicate the spot and re-saved the image:
http://cs.helsinki.fi/u/svenn/tethys4_cassini_big.tif

While the "brightest" color levels around the anomality are around (HEX) #ECECEC, this spot is purely white on the grayscale image.

Also, the original image format was JPG - and when comparing the pixel layout around the area where the anomality occurs, the image encoding has encoded this white spot differently. The craters around this spot are smooth, but the spot itself is quite sharp.. so it obviously differs from the rest of the surface.

Would you happen to know what this spot could be? If it's on the surface, it clearly reflects the sunlight better than rest of the surface. If it's not on the surface, could be some piece of rock just about to hit the surface? ..or some interference in Cassini's camera?

Best Regards,
Mikael Svenn,
Helsinki / Finland

[Chris Peterson]

I was adviced to refer here on this matter, so..
Would any of you happen to know what this white spot is in the image?

It appears to be a cosmic ray strike on the sensor. If the image was calibrated with darks or flats, it could also be the product of a cosmic ray strike on one of the calibration frames. In any case, it is certainly an artifact of the imaging process, and doesn't represent anything actually present on or in front of Tethys.