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15-meter ice spikes predicted at Europa's equator

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https://www.nature.com/articles/s41561-018-0235-0

Scientists forecast that conditions on Europa are favorable for huge spikes of ice to form via sublimation, based on current understanding of the same phenomenon on Earth. No direct observations yet. If true, this might complicate design of future landers.

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Like those cute little feathery things I see on plants after a fog in winter here? But the size of a sauropod? The solar system is always full of surprises. What other wonders do those worlds hold? :o

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Posted (edited)

Hehe. I read it too and it reminded me of the spikes on Pol :-)

And like in KSP it may be advisable to send a probe for cartography before choosing a landing site. You might step on something sharp and pointy ....

Edited by Green Baron
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3 hours ago, Green Baron said:

Hehe. I read it too and it reminded me of the spikes on Pol :-)

That is also where my mind immediately went.

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The abstract so you don't need to click the link:

Quote

On Earth, the sublimation of massive ice deposits at equatorial latitudes under cold and dry conditions in the absence of any liquid melt leads to the formation of spiked and bladed textures eroded into the surface of the ice. These sublimation-sculpted blades are known as penitentes. For this process to take place on another planet, the ice must be sufficiently volatile to sublimate under surface conditions and diffusive processes that act to smooth the topography must operate more slowly. Here we calculate sublimation rates of water ice across the surface of Jupiter’s moon Europa. We find that surface sublimation rates exceed those of erosion by space weathering processes in Europa’s equatorial belt (latitudes below 23°), and that conditions would favour penitente growth. We estimate that penitentes on Europa could reach 15 m in depth with a spacing of 7.5 m near the equator, on average, if they were to have developed across the interval permitted by Europa’s mean surface age. Although available images of Europa have insufficient resolution to detect surface roughness at the multi-metre scale, radar and thermal data are consistent with our interpretation. We suggest that penitentes could pose a hazard to a future lander on Europa.

Wikipedia article on the structures (on Earth):

https://en.wikipedia.org/wiki/Penitente_(snow_formation)

Pictures of structures on Earth comparable to the predicted ones on Europa:

Penitentes_Upper_Rio_Blanco_Argentine.jp

Snow_penitentes_Mount_Rainier.JPG

800px-Penitentes_Agua_Negra.JPG

800px-Penitentes_Ice_Formations.png

800px-Penitentes_Ice_Formations.png

If the surface is like that, then the reflection of sunlight must be diffuse and affect the albedo. The bond albedo vs geometric albedo might tells us how smooth the surface is without actually having to get super close. Although I don't think it could tell you if you have 15cm spikes packed close together, or 15 m spikes farther apart.

Geometric albedo assumes diffuse scattering of light... a mirror flat smooth ice surface (like a freshly frozen lake) would not behave like this.

I think having all those nooks and crannies would also mean that there would be a strong opposition effect.

Without being able to read the full paper, I wonder if the authors looked into available data on Europa to see if these observations are consistent.

https://en.wikipedia.org/wiki/Bond_albedo

https://en.wikipedia.org/wiki/Geometric_albedo

https://en.wikipedia.org/wiki/Opposition_surge

The albedo pages give values for Enceladus... and based on my understanding, it implies a very rough surface at the small scale.

Quote

For very bright, solid, airless objects such as Saturn's moons Enceladus and Tethys, whose total reflectance (Bond albedo) is close to one, a strong opposition effect combines with the high Bond albedo to give them a geometric albedo above unity (1.4 in the case of Enceladus). Light is preferentially reflected straight back to its source even at low angle of incidence such as on the limb or from a slope, whereas a Lambertian surface would scatter the radiation much more broadly. A geometric albedo above unity means that the intensity of light scattered back per unit solid angle towards the source is higher than is possible for any Lambertian surface.

The opposition effect seems to be mainly due to "shadow hiding" at low phase angles, which only works if the surface has a lot of shadows, which only works if the surface is very rough to produce those shadows.

So might Enceladus have these spikes too?

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I don't find this that surprising, we have directly imaged this type of terrain on Callisto. 

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You mean its not a perfectly smooth ball?! Preposterous!! Heresy!! 

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4 hours ago, MinimumSky5 said:

I don't find this that surprising, we have directly imaged this type of terrain on Callisto. 

Care to provide these images?

The closest I found was this:

PIA03455_hires.jpg

https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA03455

I'm not sure this is so similar to what they are talking about in that paper.

In particular, pay attention to the 5km scale bar.

Quote

The knobby terrain seen throughout the top inset is unlike any seen before on Jupiter's moons. The spires are very icy but also contain some darker dust. As the ice erodes, the dark material apparently slides down and collects in low-lying areas. Over time, as the surface continues to erode, the icy knobs will likely disappear, producing a scene similar to the bottom inset. The number of impact craters in the bottom image indicates that erosion has essentially ceased in the dark plains shown in that image, allowing impact craters to persist and accumulate.

The knobs are about 80 to 100 meters (260 to 330 feet) tall, and they may consist of material thrown outward from a major impact billions of years ago. The areas captured in the images lie south of Callisto's large Asgard impact basin.

I doubt they are formed by the same process as the earthly examples that were given.

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It would be fun to stick my finger into one and vaporize it with my body temperature untill it collapses, or it least make a hole in it.

9 hours ago, p1t1o said:

You mean its not a perfectly smooth ball?! Preposterous!! Heresy!! 

But hey, thats still makes good Sci-Fi scenery, right?

So, the fantastic lunar landscapes from pre-Apollo Sci-Fi really aren't that fictional after all. Just not on OUR Moon.

14387347151_d6e6d02936_z.jpg

Voyagedanslalune1.jpg

SPCSPCSPC331953.jpg

DestinationMoon-surface.jpg

Now im waiting for them to find a dry lake, too.

Edited by NSEP
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6 hours ago, NSEP said:

Now im waiting for them to find a dry lake, too.

Bet there's one on Mars somewhere, with cracks and everything. 

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On 10/10/2018 at 4:47 AM, p1t1o said:

You mean its not a perfectly smooth ball?! Preposterous!! Heresy!! 

I see what you did there.

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Spoiler

So, was that Europa Report not a documentary?!
There was no spikes. But was an octopussy.

Btw, as there are spikes like in Armageddon, they will need one thing more:

600px-Armag_310.jpg600px-Armageddon_Minigun.jpg

 

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