APOD: The Fractured North Pole of Saturn's... (2015 Oct 21)

[APOD Robot]

The Fractured North Pole of Saturn's Enceladus

Explanation: The north pole of Saturn's moon Enceladus is unexpectedly fascinating and complex. Previous to the latest flyby of the robotic Cassini spacecraft, the northern region was known mostly for its unusually high abundance of craters. Last week's flyby, however, returned images of unprecedented detail, including the featured image showing the expected craters coupled with an unexpected and circuitous pattern of picturesque cracks and fractures. Broken terrain has been recorded at lower latitudes, with deep canyons dubbed Tiger Stripes near Enceladus' South Pole. The fractures may further indicate global interplay between the surface and potential seas underneath, seas that future missions might target for signs of life.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[Boomer12k]

WOW, what a pic!!

Hope there is life, but there have only been found "simple organic carbon containing compounds" around the "tiger stripes"....maybe deeper in the interior where it could be warmer/hotter because of the Tidal Heating...but I kinda doubt it... You don't get life from just water, you need CELLULOSE....Earth is abundant. Enceladus? Maybe not so much. But some bacteria can produce it. So, if present, there is a chance, with other right circumstances.
But at least we know where to go for a drink of water. We could also use Electrolysis and make Hydrogen, and get Oxygen...and we may even be able to harvest the geysers in space and not even have to land.

Heres Hoping...
:---[===] *

[workgazer]

All life needs is a form of energy, no need for light. If bacteria are present in large quanties then something could evolve to use or eat them, some thing could predate that, think global scale blacksmokers of our own deep oceans.

Any idea why all the fractures are running top to bottom, they alsoapear to run up and over the crater edges, i assume that means the crater is older than the fracture?

[hoohaw]

Is the vertical scale exaggerated?

[geckzilla]

Is the vertical scale exaggerated?

Nope, this is how Enceladus actually appears. This is not a rendering. It looks a bit unreal because some of the spots are so bright that the details were lost in the highlights. The contrast is extremely harsh in the shadowed regions which does make it look almost like a 3D rendering with some rudimentary ray tracing. I think the blackness and the horizon was filled with pure black, too. Normally there's some diagonal grainy stripes in Cassini's imagery.

[Ann]

Love that stark whiteness of Enceladus!

And the craters seem "softened", not really sharp-edged, as if they had melted. And all those thin fractures are fascinating.

Great APOD!

Ann

[neufer]

Broken terrain has been recorded at lower latitudes, with deep canyons dubbed Tiger Stripes near Enceladus' South Pole. The fractures may further indicate global interplay between the surface and potential seas underneath, seas that future missions might target for signs of life.

[b][size=150][color=#0000FF]Here be Serpentine[/color][/size][/b]

---

Geochemical process on Saturn’s moon linked to life’s origin

<<New work from a team including Carnegie’s Christopher Glein has revealed the pH of water spewing from a geyser-like plume on Saturn’s moon Enceladus. The present team, including lead author Glein, John Baross of the University of Washington, and J. Hunter Waite Jr. of the Southwest Research Institute, developed a new chemical model based on mass spectrometry data of ice grains and gases in Enceladus’ plume gathered by Cassini, in order to determine the pH of Enceladus’ ocean. The team’s model, constrained by observational data from two Cassini teams, including one led by coauthor Waite, shows that the plume, and by inference the ocean, is salty with an alkaline pH of about 11 or 12, which is similar to that of glass-cleaning solutions of ammonia.

The model suggests that the ocean’s high pH is caused by a metamorphic, underwater geochemical process called serpentinization. On Earth, serpentinization occurs when certain kinds of so-called “ultrabasic” or “ultramafic” rocks (low in silica and high in magnesium and iron) are brought up to the ocean floor from the upper mantle and chemically interact with the surrounding water molecules. Through this process, the ultrabasic rocks are converted into new minerals, including the mineral serpentine, after which the process is named, and the fluid becomes alkaline. On Enceladus, serpentinization would occur when ocean water circulates through a rocky core at the bottom of its ocean.

“Why is serpentinization of such great interest? Because the reaction between the metallic rocks and the ocean water also produces molecular hydrogen (H₂), which provides a source of chemical energy that is essential for supporting a deep biosphere in the absence of sunlight inside moons and planets,” Glein said.>>

[Ron-Astro Pharmacist]

On the animation in the "latest flyby" link it almost appears Enceladus is could be self-propelled by its jets. Of course it's not undergoing propulsion but it will garner a lot of attention years from now if NASA could JET to Enceladus and Titan and return LIFE.

[starsurfer]

This is an incredibly detailed and mystical image of one of my many favourite moons of Saturn! Not only does the whole moon look very interesting but also a small part. Could the fractures be the result of cryovolcanism?

[MarkBour]

"Here be Serpentine". I love it.
What is the surface of Enceladus made of ? It appears to be mostly ice (?)

[Chris Peterson]

"Here be Serpentine". I love it.
What is the surface of Enceladus made of ? It appears to be mostly ice (?)

The surface is primarily water ice.

[Tekijä]

Toward the lower border is a horizontal "linear crater" which seems a bit different. Perhaps a meteor snowballed tangentially from left to right or the other way, causing a "snowball track". Without rolling of course.

[MarkBour]

"Here be Serpentine". I love it.
What is the surface of Enceladus made of ? It appears to be mostly ice (?)

The surface is primarily water ice.

So, Enceladus shows us how meteor impacts look on an ice ball. If the ice layer was thin enough, over a subsurface ocean, then you would tend to get "punctures of the windshield". I also wonder what other features you'd get, if the meteor heated up the subsurface layer enough to have some after-effect. If the ice is thick enough, as it appears to be here, you should get some melting and flow as the material re-froze, I suppose(?) The impact craters in this image look different than they do on our rocky moon. I don't see any crater rims, and I don't see any central upwelling in them. Also, no rays. I think that meteors striking Enceladus tend to bury themselves nicely in the ice, and it then tends to smooth itself out somewhat after the impact. I'd love to watch a meteor strike to see.

[Ron-Astro Pharmacist]

Toward the lower border is a horizontal "linear crater" which seems a bit different. Perhaps a meteor snowballed tangentially from left to right or the other way, causing a "snowball track". Without rolling of course.

Now I know how bobsledding got its start. How it ends is another matter.

[Chris Peterson]

If the ice is thick enough, as it appears to be here, you should get some melting and flow as the material re-froze, I suppose(?) The impact craters in this image look different than they do on our rocky moon.

In fact, the material doesn't much matter. Ice and rock crater the same way. What may change the cratering more is nonisotropic materials, layered materials, or impact speed. Neither melting nor flow are likely to be significant factors, except for very low speed impacts. And while low speed impacts (as low as 240 m/s) are possible on Enceladus, they are likely to be rare, given that the environment is dominated by Saturn's gravitational field. Most impacts are likely to much faster- tens of kilometers per second. At those speeds, material is vaporized and it doesn't matter if it's rock or ice.

In this case, the main reason the craters look different is probably because we have a tectonically active surface (unlike the Moon), so most features are new, and most are being remodeled at a pretty high rate.

[MarkBour]

In fact, the material doesn't much matter. Ice and rock crater the same way. What may change the cratering more is nonisotropic materials, layered materials, or impact speed. Neither melting nor flow are likely to be significant factors, except for very low speed impacts. And while low speed impacts (as low as 240 m/s) are possible on Enceladus, they are likely to be rare, given that the environment is dominated by Saturn's gravitational field. Most impacts are likely to much faster- tens of kilometers per second. At those speeds, material is vaporized and it doesn't matter if it's rock or ice.

After reading your answer, and realizing that you have a lot more of this sorted out than I had even thought to ask, I started looking around the net, and discovered that folks have been watching Earth's moon and have caught some live meteor impacts on its surface. A really cool event in Sep 2013 was captured (http://www.space.com/24789-moon-meteori ... osion.html), and they even seem to have estimates for its impactor mass: 400kg, speed: 61000 km/h, diameter: ~ 1m. And the resulting crater was apparently about 40m in diameter. However, I don't know how they would have obtained these estimates. I'll try to read more about it. A basic question, though, would be: Can you look at a crater and make many deductions about the impactor based on simply the size and shape of the crater? I wonder at the physics that would inform such deductions.

[neufer]

I started looking around the net, and discovered that folks have been watching Earth's moon and have caught some live meteor impacts on its surface. A really cool event in Sep 2013 was captured (http://www.space.com/24789-moon-meteori ... osion.html), and they even seem to have estimates for its impactor mass: 400kg, speed: 61000 km/h, diameter: ~ 1m. And the resulting crater was apparently about 40m in diameter. However, I don't know how they would have obtained these estimates. I'll try to read more about it. A basic question, though, would be: Can you look at a crater and make many deductions about the impactor based on simply the size and shape of the crater? I wonder at the physics that would inform such deductions.

61000 km/h = 17 km/sec is actually incredibly slow for a meteor hitting the moon considering that the Earth/Moon are already moving at ~30 km/sec. The slowest major meteor shower is the 24km/sec Alpha Capricornid shower (July 11th to August 10th). More likely it was probably assumed that this September 11th impactor was an early 17 mile/sec (28km/sec) meteor from the Southern Taurid meteor shower (September 7th to November 19th). Once the speed is assumed the impactor mass/diameter would be a simple function of the crater size.

[MarkBour]

Once the speed is assumed the impactor mass/diameter would be a simple function of the crater size.

I can imagine this statement to be true if you are talking about a relatively constant set of materials (the make-up of the impactor and of the impacted landscape, that is). And if you're using knowledge of past events to calibrate this. Or are you able to deduce this from deeper principles? Although Chris made a comment that craters form pretty much the same in ice or rock landscapes, I'm not sure he meant to indicate that size would be the same as well.

Certainly if a meteor hits an ocean, you get nothing. If it hits a thin ice shell above a liquid ocean, you get the smallest possible crater, perhaps -- just the size of the meteor. If a solid body hits something else solid (neither of which are strangely explosive) and the meteor vaporizes, that's what we're talking about ... is the size independent of the materials? That sounds too good to be true. But perhaps one of you will tell me that you can figure out precisely that.

I'm kind of hoping you'll answer that we need more data. I think it would be fun to run some experiments to calibrate the expected size. I guess speeds are typically like 10-50 times the speed of a rifle bullet, so it would be hard to try this at full scale in a lab. Hurling rocks at high velocity at an asteroid (in the name of science, of course) sounds like a bit of fun.

[Chris Peterson]

Once the speed is assumed the impactor mass/diameter would be a simple function of the crater size.

I can imagine this statement to be true if you are talking about a relatively constant set of materials (the make-up of the impactor and of the impacted landscape, that is). And if you're using knowledge of past events to calibrate this. Or are you able to deduce this from deeper principles? Although Chris made a comment that craters form pretty much the same in ice or rock landscapes, I'm not sure he meant to indicate that size would be the same as well.

To a large degree, the size of the crater is determined by the kinetic energy of the impact (that is, the mass and speed of the impactor). For a wide range of realistic impact surfaces, the material simply isn't very important. At hypersonic speeds, the impactor is moving much faster than the velocity of sound in the medium, which tends to normalize the cratering physics across most surface types.

Certainly if a meteor hits an ocean, you get nothing. If it hits a thin ice shell above a liquid ocean, you get the smallest possible crater, perhaps -- just the size of the meteor. If a solid body hits something else solid (neither of which are strangely explosive) and the meteor vaporizes, that's what we're talking about ... is the size independent of the materials? That sounds too good to be true. But perhaps one of you will tell me that you can figure out precisely that.

Not independent, but not nearly as dependent as you would think. Yes, you can construct extreme cases like thin ice or deep sand impacts. But these aren't typical for most of what we actually see in the Solar System- impacts on deep rock, deep ice, or a mixture of the two.

I'm kind of hoping you'll answer that we need more data. I think it would be fun to run some experiments to calibrate the expected size. I guess speeds are typically like 10-50 times the speed of a rifle bullet, so it would be hard to try this at full scale in a lab. Hurling rocks at high velocity at an asteroid (in the name of science, of course) sounds like a bit of fun.

Much of our basic understanding of cratering processes comes from shooting very high velocity pellets using tools like the Ames Vertical Gun Range. In addition, modern supercomputers are able to numerically model high speed collisions with (apparently) great accuracy. As such things go, the physics and the models are fairly simple.

[MarkBour]

Hurling rocks at high velocity at an asteroid (in the name of science, of course) sounds like a bit of fun.

Much of our basic understanding of cratering processes comes from shooting very high velocity pellets using tools like the Ames Vertical Gun Range. In addition, modern supercomputers are able to numerically model high speed collisions with (apparently) great accuracy. As such things go, the physics and the models are fairly simple.

Dang! They beat me to it. (It's depressing that whenever I have an idea like this, it seems that NASA not only beat me to it, but they did it a very long time ago. )

Anyway, thanks for the pointer to this, it was fun reading about this gun and the highly developed complementary experimental apparatus ! (Probably lots more fun to get a tour of the place.)

I'm also still trying to imagine roughly what happens in these collisions. I think I started with a false notion that there are explosive materials, like TNT, and non-explosive materials, such as a rock. But perhaps in these circumstances the distinction breaks down. When an otherwise non-volatile rock hits a sufficiently big, deep pile of dirt ... at 30,000 m/s. I guess all of that kinetic energy has to be converted rapidly to heat energy as the rock decelerates. So, does this heat vaporize molecules of the rock and many of the dirt molecules into a gaseous phase? Which thus explodes? I'm beginning to see that this is really not very different than what I've thought of as explosives.