APOD: Ganymede from Juno (2021 Jun 14)

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APOD: Ganymede from Juno (2021 Jun 14)

Post by APOD Robot » Mon Jun 14, 2021 4:09 am

Image Ganymede from Juno

Explanation: What does the largest moon in the Solar System look like? Jupiter's moon Ganymede, larger than even Mercury and Pluto, has an icy surface speckled with bright young craters overlying a mixture of older, darker, more cratered terrain laced with grooves and ridges. The cause of the grooved terrain remains a topic of research, with a leading hypothesis relating it to shifting ice plates. Ganymede is thought to have an ocean layer that contains more water than Earth -- and might contain life. Like Earth's Moon, Ganymede keeps the same face towards its central planet, in this case Jupiter. The featured image was captured last week by NASA's robotic Juno spacecraft as it passed only about 1000 kilometers above the immense moon. The close pass reduced Juno's orbital period around Jupiter from 53 days to 43 days. Juno continues to study the giant planet's high gravity, unusual magnetic field, and complex cloud structures.

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Ann » Mon Jun 14, 2021 4:46 am

Last edited by Ann on Mon Jun 14, 2021 9:15 am, edited 1 time in total.
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Chris Peterson » Mon Jun 14, 2021 5:18 am

Ann wrote:
Mon Jun 14, 2021 4:46 am

It is interesting to contemplate the similarities and differences of our own Moon and Ganymede.

It's easy to see how the impact craters got there, but what about the general surface markings?
The difference between being made of rock and being made of ice?
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by VictorBorun » Mon Jun 14, 2021 6:06 am

this monochromatic image shows dark low plains and white highlands.

A lower resolution color 3d model also renders lowlands as dark but different plains with different thickness of brown: thinner brown is yellowish. I have tried to rotate the 3d Ganymede at the visual applet and then rotated 90° counter-clockwise to somewhat fit the posted high resolution pic:
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by VictorBorun » Mon Jun 14, 2021 6:16 am

Chris Peterson wrote:
Mon Jun 14, 2021 5:18 am
The difference between being made of rock and being made of ice?
"underground saltwater ocean on Ganymede" does not imply an icy surface. It can all be proper rock.

By the way, how has smaller Titan managed to grow a thicker atmosphere?

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Alex_515 » Mon Jun 14, 2021 7:36 am

On the left part of the image, middle, between the dark rectangular area and a bright area, there is a strange alignment of small craters.

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Chris Peterson » Mon Jun 14, 2021 7:41 am

VictorBorun wrote:
Mon Jun 14, 2021 6:16 am
Chris Peterson wrote:
Mon Jun 14, 2021 5:18 am
The difference between being made of rock and being made of ice?
"underground saltwater ocean on Ganymede" does not imply an icy surface. It can all be proper rock.

By the way, how has smaller Titan managed to grow a thicker atmosphere?
There's no known geological mechanism for creating a body consisting of a rocky crust on top of a thick layer of water.

In any case, spectroscopic data reveal that the surface of Ganymede is made of ice, primarily water ice, but also various other ices as well.
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by JohnD » Mon Jun 14, 2021 9:06 am

AHEM! "no known geological mechanism"???

Chris, see: https://www.theguardian.com/environment ... rrier-reef Underwater eruptions produce pumice, lava so full of gas that when solidified, it floats.

How long it can go on flaoting is the subject of research: https://www.universityofcalifornia.edu/ ... cks-pumice

And thank you for a thoroughly 'scientific' APOD - and beautiful as well!

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Chris Peterson » Mon Jun 14, 2021 9:13 am

JohnD wrote:
Mon Jun 14, 2021 9:06 am
AHEM! "no known geological mechanism"???

Chris, see: https://www.theguardian.com/environment ... rrier-reef Underwater eruptions produce pumice, lava so full of gas that when solidified, it floats.

How long it can go on flaoting is the subject of research: https://www.universityofcalifornia.edu/ ... cks-pumice

And thank you for a thoroughly 'scientific' APOD - and beautiful as well!

JOhn
Again, there is no known geological mechanism for a rocky crust floating on a thick water layer. We're not talking about some bits of rock that have a density less than water due to trapped gas, but the entire crust of a planetary body! Ganymede is a fairly conventional terrestrial body- an iron core, surrounded by a rocky mantle, with an outer ocean, the uppermost part of which is frozen.
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Ann » Mon Jun 14, 2021 9:16 am

Chris Peterson wrote:
Mon Jun 14, 2021 5:18 am
Ann wrote:
Mon Jun 14, 2021 4:46 am

It is interesting to contemplate the similarities and differences of our own Moon and Ganymede.

It's easy to see how the impact craters got there, but what about the general surface markings?
The difference between being made of rock and being made of ice?
Right, Chris. That ought to make a difference, I agree.

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by JohnD » Mon Jun 14, 2021 9:22 am

Chris Peterson wrote:
Mon Jun 14, 2021 9:13 am
JohnD wrote:
Mon Jun 14, 2021 9:06 am
AHEM! "no known geological mechanism"???

Chris, see: https://www.theguardian.com/environment ... rrier-reef Underwater eruptions produce pumice, lava so full of gas that when solidified, it floats.

How long it can go on flaoting is the subject of research: https://www.universityofcalifornia.edu/ ... cks-pumice

And thank you for a thoroughly 'scientific' APOD - and beautiful as well!

JOhn
Again, there is no known geological mechanism for a rocky crust floating on a thick water layer. We're not talking about some bits of rock that have a density less than water due to trapped gas, but the entire crust of a planetary body! Ganymede is a fairly conventional terrestrial body- an iron core, surrounded by a rocky mantle, with an outer ocean, the uppermost part of which is frozen.
OK, point taken, but there IS a geological mechanism!

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by javachip2 » Mon Jun 14, 2021 10:57 am

Is this photo the Jovian or anti-Jovian hemisphere? Earth's moon is significantly more cratered on the far side than the near side. Is this also true of Ganymede? How does the difference between Jovian and anti-Jovian compare with the difference between leading and trailing hemispheres in terms of cratering?

If Ganymede's crust is mostly water ice, it's interesting that impact craters look similar to those on our Moon. Impacts entail the release of vast amounts of thermal energy, which should cause widespread changes if the surface melts at 0C rather than 1000C.

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by VictorBorun » Mon Jun 14, 2021 12:16 pm

offtopic
Our notion of Earth's Moon seems to have already got influenced by telescopic images. Delivering you the moon advertisment features Moon rather than the moon of the cry for the moon phrase.

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by VictorBorun » Mon Jun 14, 2021 12:28 pm

Chris Peterson wrote:
Mon Jun 14, 2021 7:41 am
In any case, spectroscopic data reveal that the surface of Ganymede is made of ice, primarily water ice, but also various other ices as well.
I wonder what ices give Ganymede its brown tint

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by orin stepanek » Mon Jun 14, 2021 12:29 pm

VaultOutput.png
Kinda looks like the continents may be submerged inside the ocean! :roll:

0100358.jpg
Kitty better not fall in the watering can; it may be full of water! :wink:
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by neufer » Mon Jun 14, 2021 1:53 pm

https://en.wikipedia.org/wiki/Ganymede_(moon) wrote: <<Ganymede is composed of approximately equal amounts of silicate rock and water. It is a fully differentiated body with an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth's oceans combined. Its surface is composed of two main types of terrain. Dark regions, saturated with impact craters and dated to four billion years ago, cover about a third of it. Lighter regions, crosscut by extensive grooves and ridges and only slightly less ancient, cover the remainder. The cause of the light terrain's disrupted geology is not fully known, but was likely the result of tectonic activity due to tidal heating. The dark terrain, which comprises about one-third of the surface, contains clays and organic materials that could indicate the composition of the impactors from which Jovian satellites accreted.

Cratering is seen on both types of terrain, but is especially extensive on the dark terrain: it appears to be saturated with impact craters and has evolved largely through impact events. The brighter, grooved terrain contains many fewer impact features, which have been only of a minor importance to its tectonic evolution. The density of cratering indicates an age of 4 billion years for the dark terrain, similar to the highlands of the Moon, and a somewhat younger age for the grooved terrain (but how much younger is uncertain). Ganymede may have experienced a period of heavy cratering 3.5 to 4 billion years ago similar to that of the Moon. If true, the vast majority of impacts happened in that epoch, whereas the cratering rate has been much smaller since. Craters both overlay and are crosscut by the groove systems, indicating that some of the grooves are quite ancient. Relatively young craters with rays of ejecta are also visible. Ganymedian craters are flatter than those on the Moon and Mercury. This is probably due to the relatively weak nature of Ganymede's icy crust, which can (or could) flow and thereby soften the relief. Ancient craters whose relief has disappeared leave only a "ghost" of a crater known as a palimpsest.

The heating mechanism required for the formation of the grooved terrain on Ganymede is an unsolved problem in the planetary sciences. The modern view is that the grooved terrain is mainly tectonic in nature. Cryovolcanism is thought to have played only a minor role, if any. The forces that caused the strong stresses in the Ganymedian ice lithosphere necessary to initiate the tectonic activity may be connected to the tidal heating events in the past, possibly caused when the satellite passed through unstable orbital resonances. The tidal flexing of the ice may have heated the interior and strained the lithosphere, leading to the development of cracks and horst and graben faulting, which erased the old, dark terrain on 70% of the surface. The formation of the grooved terrain may also be connected with the early core formation and subsequent tidal heating of Ganymede's interior, which may have caused a slight expansion of Ganymede by 1–6% due to phase transitions in ice and thermal expansion. During subsequent evolution deep, hot water plumes may have risen from the core to the surface, leading to the tectonic deformation of the lithosphere. Radiogenic heating within the satellite is the most relevant current heat source, contributing, for instance, to ocean depth. Research models have found that if the orbital eccentricity were an order of magnitude greater than currently (as it may have been in the past), tidal heating would be a more substantial heat source than radiogenic heating.>>
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by johnnydeep » Mon Jun 14, 2021 7:44 pm

Alex_515 wrote:
Mon Jun 14, 2021 7:36 am
On the left part of the image, middle, between the dark rectangular area and a bright area, there is a strange alignment of small craters.
[I do wish people would post pictures!...] But I assume you're talking about this nicely linear grouping of sometimes slightly overlapping craters:

linear craters on ganymede.JPG

My guess is it was caused by an asteroid that broke apart on it's way in (like that string of comet fragments that hit Jupiter in 1994 - see https://solarsystem.nasa.gov/resources/ ... iter-1994/), or perhaps this was a case of a "stone skipping on water" effect?
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Enki Catena

Post by neufer » Mon Jun 14, 2021 9:04 pm

johnnydeep wrote:
Mon Jun 14, 2021 7:44 pm
Alex_515 wrote:
Mon Jun 14, 2021 7:36 am

On the left part of the image, middle, between the dark rectangular area and a bright area, there is a strange alignment of small craters.
My guess is it was caused by an asteroid that broke apart on it's way in (like that string of comet fragments that hit Jupiter in 1994 - see https://solarsystem.nasa.gov/resources/ ... iter-1994/), or perhaps this was a case of a "stone skipping on water" effect?
https://en.wikipedia.org/wiki/Crater_chain wrote: <<A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena, plural catenae (Latin for "chain"), as specified by the International Astronomical Union's rules on planetary nomenclature.

Many examples of such chains are thought to have been formed by the impact of a body that was broken up by tidal forces into a string of smaller objects following roughly the same orbit. An example of such a tidally disrupted body that was observed prior to its impact on Jupiter is Comet Shoemaker-Levy 9. During the Voyager observations of the Jupiter system, planetary scientists identified 13 crater chains on Callisto and three on Ganymede (except those formed by secondary craters). Later some of these chains turned out to be secondary or tectonic features, but some other chains were discovered. As of 1996, 8 primary chains on Callisto and 3 on Ganymede were confirmed.

Other cases, such as many of those on Mars, represent chains of collapse pits associated with grabens (see, for example, the Tithoniae Catenae near Tithonium Chasma). Crater chains seen on the Moon often radiate from larger craters, and in such cases are thought to be either caused by secondary impacts of the larger crater's ejecta or by volcanic venting activity along a rift.>>
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Re: Enki Catena

Post by johnnydeep » Mon Jun 14, 2021 9:09 pm

neufer wrote:
Mon Jun 14, 2021 9:04 pm
johnnydeep wrote:
Mon Jun 14, 2021 7:44 pm
Alex_515 wrote:
Mon Jun 14, 2021 7:36 am

On the left part of the image, middle, between the dark rectangular area and a bright area, there is a strange alignment of small craters.
My guess is it was caused by an asteroid that broke apart on it's way in (like that string of comet fragments that hit Jupiter in 1994 - see https://solarsystem.nasa.gov/resources/ ... iter-1994/), or perhaps this was a case of a "stone skipping on water" effect?
https://en.wikipedia.org/wiki/Crater_chain wrote: <<A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena, plural catenae (Latin for "chain"), as specified by the International Astronomical Union's rules on planetary nomenclature.

Many examples of such chains are thought to have been formed by the impact of a body that was broken up by tidal forces into a string of smaller objects following roughly the same orbit. An example of such a tidally disrupted body that was observed prior to its impact on Jupiter is Comet Shoemaker-Levy 9. During the Voyager observations of the Jupiter system, planetary scientists identified 13 crater chains on Callisto and three on Ganymede (except those formed by secondary craters). Later some of these chains turned out to be secondary or tectonic features, but some other chains were discovered. As of 1996, 8 primary chains on Callisto and 3 on Ganymede were confirmed.

Other cases, such as many of those on Mars, represent chains of collapse pits associated with grabens (see, for example, the Tithoniae Catenae near Tithonium Chasma). Crater chains seen on the Moon often radiate from larger craters, and in such cases are thought to be either caused by secondary impacts of the larger crater's ejecta or by volcanic venting activity along a rift.>>
Thanks! I still like my skipping stone idea though :)
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by MarkBour » Tue Jun 15, 2021 12:59 am

I'm struck by the white areas around the largest impact sites. At least they appear white in this image. I guess that when a large impact occurs on Ganymede, what gets thrown up includes a bunch of the subsurface water (saltwater?) which then falls back and freezes on the surface.
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by Chris Peterson » Tue Jun 15, 2021 1:18 am

MarkBour wrote:
Tue Jun 15, 2021 12:59 am
I'm struck by the white areas around the largest impact sites. At least they appear white in this image. I guess that when a large impact occurs on Ganymede, what gets thrown up includes a bunch of the subsurface water (saltwater?) which then falls back and freezes on the surface.
Hypervelocity impacts produce very little melt, whether in ice or rock. Much of the excavated material is almost instantly vaporized, and a lot of what is ejected never has a chance to change phase. You get shocked material (metamorphosed in the case of rock), and some surface melting, but it's unlikely much liquid was spread around, and the crust is probably too thick for most impacts to penetrate to any underlying liquid ocean. Given an icy crust, we can figure that the surface will have some mineral deposits, as well as a lot of space weathering, which produces dark areas. An impact exposes and ejects clean ice, which is close to white.

As always with these images, we've got to be careful with interpreting color and intensity. Images are likely stretched to cover a range from white to black, which hides the true differences between areas. For that we'd need to look at unprocessed, linear images.
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by emc » Tue Jun 15, 2021 1:54 am

Chris Peterson wrote:
Tue Jun 15, 2021 1:18 am
As always with these images, we've got to be careful with interpreting color and intensity. Images are likely stretched to cover a range from white to black, which hides the true differences between areas. For that we'd need to look at unprocessed, linear images.
Always careful

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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by orin stepanek » Tue Jun 15, 2021 12:10 pm

What intrigues me more is the dark area that seems to be inlaid like
a piece of tile!
file.jpg
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by johnnydeep » Tue Jun 15, 2021 12:39 pm

orin stepanek wrote:
Tue Jun 15, 2021 12:10 pm
What intrigues me more is the dark area that seems to be inlaid like
a piece of tile!

file.jpg
if you look at neufer's post above showing a higher-res image of the same area, there is less of a contrast between the two sides, and the primary difference is smoothness and crater density, presumably indicative of relative age (smoother, less cratered being younger and lighter due to less "space weathering"). Still, the almost straight lines and right angles are indeed interesting.
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Re: APOD: Ganymede from Juno (2021 Jun 14)

Post by JohnD » Tue Jun 22, 2021 8:35 am

What ever happened to "craterchains", the apocalyptic contributor who argued they were evidence of prehistoric interplanetary warfare?
He would have loved this!