APOD: Enceladus: Ringside Water World (2015 Dec 03)

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APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by APOD Robot » Thu Dec 03, 2015 5:13 am

Image Enceladus: Ringside Water World

Explanation: Saturn's icy moon Enceladus poses above the gas giant's icy rings in this Cassini spacecraft image. The dramatic scene was captured on July 29, while Cassini cruised just below the ring plane, its cameras looking back in a nearly sunward direction about 1 million kilometers from the moon's bright crescent. At 500 kilometers in diameter, Enceladus is a surprisingly active moon though, its remarkable south polar geysers are visible venting beyond a dark southern limb. In fact, data collected during Cassini's flybys and years of images have recently revealed the presence of a global ocean of liquid water beneath this moon's icy crust. Demonstrating the tantalizing liquid layer's global extent, the careful analysis indicates surface and core are not rigidly connected, with Enceladus rocking slightly back and forth in its orbit.

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Indigo_Sunrise » Thu Dec 03, 2015 11:26 am

This is an awesome APOD! I especially like that some 'geyser action' can be seen.
Very cool!

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by bls0326 » Thu Dec 03, 2015 1:44 pm

+1 Awesome APOD. Who would have thought any moon was "sloshing" around in orbit!

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by retrogalax » Thu Dec 03, 2015 2:42 pm

Beautiful conjunction !

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by heehaw » Thu Dec 03, 2015 2:46 pm

Will Cassini ever be put on a course to glide closer and closer to the rings, giving us a REALLY close up view of a section of the rings? Clumps of snowballs drifting together....

heehaw

Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by heehaw » Thu Dec 03, 2015 2:47 pm

And by the way, the largest object the New Horizons probe passed was Jupiter....

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Ann » Thu Dec 03, 2015 3:20 pm

heehaw wrote:Will Cassini ever be put on a course to glide closer and closer to the rings, giving us a REALLY close up view of a section of the rings? Clumps of snowballs drifting together....
Going in close might put the (in)famous Star Wars asteroid field scene to shame.
Click to play embedded YouTube video.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Normus Svanstukker » Thu Dec 03, 2015 3:31 pm

Waht is truly amazing is that the temperatures out there are cold enough to make water ice hard as steel. Therefore the internal temperatures of Enceladus must be warmer than zero Celsius (32F) so initially the water must be liquid as it passes through the vents. Otherwise there'd be no cryovolcanic action. I like using that word - "cryovolcanic".

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Ron-Astro Pharmacist » Thu Dec 03, 2015 4:05 pm

Is that a filling station I see around that gas giant? Well – maybe one day. I suppose Enceladus could fill that role instead… Not giving too much away Sandford, et al really tried to keep the science in science fiction. :clap:
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by MarkBour » Thu Dec 03, 2015 6:20 pm

I would love to get a large-screen TV, hang it on my living room wall, and just put a feed from Cassini on it.
That would top any other piece of art I could put there.
The top of the ring looks hazy in this image. Is there a reason for that?
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Alohascope » Thu Dec 03, 2015 8:28 pm

With comets ruled out as source of earth's water, the source of earth's water is an "open question."

http://www.esa.int/Our_Activities/Space ... h_s_oceans

With the smooth surface of Enceladus making asteroid source water highly unlikely, we might try radical thought in finding an answer to the question of where water comes from.

Concerning Enceladus' heat source we might consider bacteria. http://compost.css.cornell.edu/microorg.html

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by MarkBour » Thu Dec 03, 2015 11:22 pm

Alohascope wrote:With comets ruled out as source of earth's water, the source of earth's water is an "open question."

http://www.esa.int/Our_Activities/Space ... h_s_oceans
So, can someone explain to me why it is thought that Earth's water was not here from the beginning?
Or, to be more specific, why is it believed that Earth's original water would have "boiled away"?
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Ann » Fri Dec 04, 2015 12:37 am

MarkBour wrote:
Alohascope wrote:With comets ruled out as source of earth's water, the source of earth's water is an "open question."

http://www.esa.int/Our_Activities/Space ... h_s_oceans
So, can someone explain to me why it is thought that Earth's water was not here from the beginning?
Or, to be more specific, why is it believed that Earth's original water would have "boiled away"?
Be warned that I'm replying to this without googling any of the claims I'm making here.

It is believed that the very early Earth collided with a Mars-sized object. This was an absolutely titanic collision that utterly smashed both the Earth and the Mars-sized object to smithereens. Eventually, the present-say Earth as well as the Moon formed out of this solar system train wreck.

It is generally believed that such an immense collision would have boiled the Earth's water away. Bear in mind, too, that the Earth formed on the "warm side" of the so-called snow line in the solar system. Objects on the "cold side" of the snow line tend to be either gas giants or icy objects, because they formed out of "dirty iceballs" flying around out there. Objects on the warm side of the snow line, Mercury, Venus, Earth and Mars, are rocky objects with small amounts of ice. That's because the ice evaporated close to the young Sun, and only "dry pieces of rock" were available for planet-building in the inner solar system. Compared with the icy objects in the outer parts of the solar system, the Earth actually contains very little water.

But I think many astronomers now think that some water was still incorporated in the rocks that formed the Earth after its collision with the Mars-sized object. I think the general opinion now is that the Earth's water is a mixture of water that came here on comets and asteroids and water that was incorporated in the Earth as it formed, and which later made its way to the surface of the Earth and contributed to the formation of the oceans.

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Boomer12k » Fri Dec 04, 2015 12:54 am

Truly an AMAZING shot....

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Alohascope » Fri Dec 04, 2015 7:56 pm

Ann wrote:
MarkBour wrote:
Alohascope wrote:With comets ruled out as source of earth's water, the source of earth's water is an "open question."

http://www.esa.int/Our_Activities/Space ... h_s_oceans
So, can someone explain to me why it is thought that Earth's water was not here from the beginning?
Or, to be more specific, why is it believed that Earth's original water would have "boiled away"?
Be warned that I'm replying to this without googling any of the claims I'm making here.

It is believed that the very early Earth collided with a Mars-sized object. This was an absolutely titanic collision that utterly smashed both the Earth and the Mars-sized object to smithereens. Eventually, the present-say Earth as well as the Moon formed out of this solar system train wreck.

It is generally believed that such an immense collision would have boiled the Earth's water away. Bear in mind, too, that the Earth formed on the "warm side" of the so-called snow line in the solar system. Objects on the "cold side" of the snow line tend to be either gas giants or icy objects, because they formed out of "dirty iceballs" flying around out there. Objects on the warm side of the snow line, Mercury, Venus, Earth and Mars, are rocky objects with small amounts of ice. That's because the ice evaporated close to the young Sun, and only "dry pieces of rock" were available for planet-building in the inner solar system. Compared with the icy objects in the outer parts of the solar system, the Earth actually contains very little water.

But I think many astronomers now think that some water was still incorporated in the rocks that formed the Earth after its collision with the Mars-sized object. I think the general opinion now is that the Earth's water is a mixture of water that came here on comets and asteroids and water that was incorporated in the Earth as it formed, and which later made its way to the surface of the Earth and contributed to the formation of the oceans.

Ann
Any ideas on where the water so abundant in the 'snow side' of the solar system came from? And where the waters in comets and asteroids came from?

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by MarkBour » Sat Dec 05, 2015 12:08 am

Ann wrote:Be warned that I'm replying to this without googling any of the claims I'm making here.
Thanks for your summary, Ann. Since you mentioned it, I decided to do just that ... I googled it some more. And what I found agreed with your summary rather well. So, much is still open for debate. I liked a recent finding that I came across that indicated our water might have come primordially, and hence the inference would be that some of it (perhaps lots of it) may have survived said major collision (http://www.sciencemag.org/content/350/6262/795).
Alohascope wrote:Any ideas on where the water so abundant in the 'snow side' of the solar system came from? And where the waters in comets and asteroids came from?
The simplest idea is that there was a lot of water in the cloud that formed our Solar system ... if that's what you're asking. This still leaves a complex history of how it all ended up where it did, why some of it left parts of the system (Venus and inward, Mars), and why it remained in other places (Earth, and lots of places beyond the "snow line"). I'm betting, though, that we will learn lots more about this in coming years.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by bystander » Sat Dec 05, 2015 4:03 am

Alohascope wrote:
Any ideas on where the water so abundant in the 'snow side' of the solar system came from? And where the waters in comets and asteroids came from?

Hydrogen, Helium, and Oxygen are the three most abundant elements in the Universe. Water is a simple molecule. Hydrogen and Oxygen are both highly reactive. To me it would be amazing if there wasn't an abundance of water available while the Solar System was forming.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by Ann » Sat Dec 05, 2015 6:33 am

Alohascopa wrote:
Any ideas on where the water so abundant in the 'snow side' of the solar system came from? And where the waters in comets and asteroids came from?
Well, like bystander said, there clearly was a lot of hydrogen and oxygen in the early solar system, which easily combined into water. But now consider the snowline. On the warm side of the snowline, water is a gas. That is because it is too warm there in the protoplanetary disk for the water to be a solid (and if it is a solid, it is ice), and it can't be a liquid there, because the ambient pressure is too low. Think of it. Water is liquid on the Earth not only because Earth is the right temperature, but also because we have an atmosphere that creates just the right atmospheric pressure to force water to be liquid here.

This youtube video explains that water boils at a lower and lower temperature as you get higher and higher up on Mount Everest, and the atmospheric pressure around you keeps dropping:
Click to play embedded YouTube video.
There might have been some "atmospheric pressure" in the protoplanetay disk that the Earth formed from, so there might have droplets of water there, for all I know. But mostly, the water there was gaseous. Beyond the snow line, the water was solid. It was ice.
I once listened to an astronomer who said that making planets or moons on the cold side of the snowline is like making a snowball. You just scope up the snow and ice and compress it, along with some pebbles and gravel that happen to be mixed with the snow.

But you can't make a "liquid water ball" or a "water vapor ball" by trying to scope up water vapor and compress it. You can just grab a handful of pebbles, and the water you get is the water that might be incorporated inside the pebbles. And we really know that the pebbles in the protoplanetary disk did contain some water.

But most of the water on the warm side of the snowline probably never got incorporated in any planets at all. It just kept floating around there in molecular form in orbit around the Sun. In contrast, most of the water on the cold side of the snow line grew into large "snowballs" and turned into planets and moons, comets and asteroids. (So what happened to the asteroids that robbed them of most of their water? Well... I read about a hypothesis that there might have been a large shakeup in the early solar system, where Jupiter and Saturn first moved closer to the Sun and then turned back again. Maybe Jupiter pushed the proto-asteroids in front of it, and their ice melted and their water evaporated, and then the asteroids as we know them today formed out of those desiccated rocks... I haven't got the faintest idea.) :wink:

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by dcrouchman » Mon Dec 21, 2015 2:49 am

Could anyone please explain why the backgroud of this picture is black instead of having stars.

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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by geckzilla » Mon Dec 21, 2015 2:55 am

dcrouchman wrote:Could anyone please explain why the backgroud of this picture is black instead of having stars.
The exposure time was too short to capture enough light from background stars.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by neufer » Mon Dec 21, 2015 4:00 pm

geckzilla wrote:
dcrouchman wrote:
Could anyone please explain why the backgroud of this picture is black instead of having stars.
The exposure time was too short to capture enough light from background stars.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by geckzilla » Mon Dec 21, 2015 4:23 pm

neufer wrote:as the Earth & Venus are visible in some overexposed Cassini shots:

http://apod.nasa.gov/apod/ap060927.html
http://apod.nasa.gov/apod/ap131113.html

...but one seldom has such objects in the field of view.
Those two are special because the sun was behind Saturn. I'd hesitate at calling them overexposed, but I suppose the use of that word is a matter of personal preference.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by neufer » Mon Dec 21, 2015 10:29 pm

geckzilla wrote:
neufer wrote:
The brightest stars might just be visible
as the Earth & Venus are visible in some overexposed Cassini shots:

http://apod.nasa.gov/apod/ap060927.html
http://apod.nasa.gov/apod/ap131113.html

...but one seldom has such objects in the field of view.
Those two are special because the sun was behind Saturn. I'd hesitate at calling them overexposed, but I suppose the use of that word is a matter of personal preference.
It's overexposed compared with typical Cassini shots.

My point is that a bright star (e.g., Aldebaran, Spica, Antares, Pollux, Formalhaut, Regulus, Castor) would easily be visible in this [15º ?] wide overexposed Cassini shot. Such bright stars might also be just visible in normally exposed narrow angle shot but it would have to be a very lucky angled shot.
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Re: APOD: Enceladus: Ringside Water World (2015 Dec 03)

Post by geckzilla » Tue Dec 22, 2015 1:03 am

Then you would mean to say that the mosaic contains more lengthy exposures than is typical for Cassini's imagery. The word "overexposed" has a negative denotation.
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