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The surface of Europa is famous for all the criss-cross lines thought to be cracks in the ice above a water ocean that somehow re-freeze.

But in the photo below I also see a lot of raised "bumps" with roughly circular bases.

These are pretty tall as their shadows near the terminator can be resolved.

I hadn't heard of these before;

  • Is there a name for this kind of feature on Europa?
  • Are there processes proposed for their formation?
  • Roughly, how tall are they?

Cropped and sharpened from this tweeted image of Europa taken by the Juno spacecraft during a recent close flyby of the moon:

bumps on Europa from a Juno flyby

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  • $\begingroup$ They are called "chaos terrain". $\endgroup$
    – Heopps
    Nov 28, 2022 at 13:08
  • $\begingroup$ I've found a review about them. Not very recent, but there are a lot of pitures from Galileo spacecraft. websites.pmc.ucsc.edu/~fnimmo/website/… $\endgroup$
    – Heopps
    Nov 28, 2022 at 13:17
  • $\begingroup$ "roughly circular bases" Practically anything can be described like that. You are subconsciously adding implied detail I think. $\endgroup$
    – StephenG - Help Ukraine
    Nov 28, 2022 at 13:38
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    $\begingroup$ If you have access, here is the entry in the Encyclopedia of Planetary Landforms: doi.org/10.1007/978-1-4614-3134-3_45 including several models of the driving mechanism of their formation. $\endgroup$
    – Jean-Marie Prival
    Nov 28, 2022 at 15:22
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    $\begingroup$ Is it my imagination, or does the area occupied by the "goose bumps" have a slightly dark hue? Following on from the reference in @Jean-MariePrival's comment the bumps are called lenticulae (Latin for freckles). There are also regions with red lenticulae, which are apparently younger than the gray/blue lenticulae. I don't know if the red ones are related to the one's in your photo, but the one's I've referenced appear to be central mounds within craters - quasi circular depressions. $\endgroup$
    – Fred
    Nov 28, 2022 at 18:04

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The paper Geometry and spatial distribution of lenticulae on Europa gives a good description what is going on.

As I mention in my comment the bumps/domes are called lenticulae, Latin for freckles. In addition to the gray/blue ones in the photo there are also red ones elsewhere on Europa.

enter image description here

Lenticulae tend be "roughly elliptical" in shape and can occur as either domes or pits, or both - see the picture above. General observation of lenticulae are:

(1) pits and domes have similar sizes; (2) chaos are larger than the other lenticulae; (3) pits are clustered within the trailing antijovian quadrant and the leading subjovian quadrant whereas domes, dome/chaos, and chaos terrains are more uniformly distributed; (4) the areal density for all lenticulae is not uniform; (5) lenticulae do not divert the path of younger lineaments such as ridges.

The conceptual model for the lenticulae is that they are,

... a surface expression of dynamics within the ice shell at a different stage of lenticulae evolution. The similar size and shape of pits and domes suggests that one may evolve into the other. Because domes are more numerous and more uniformly distributed than pits, they are more likely to represent the end stage of this evolution, assuming the end-stage leaves a longer-lasting surface expression.

Other observations are:

  • That lineaments do do not offset pits
  • Pits have a preferred northwest-southeast elongation
  • Pits may be an earlier stage in the evolution of lenticulae

The lateral dimensions of the lenticulae range between a few kilometers to tens of kilometers. The heights of the domes typically vary from 40 to 100 m. The pit bottoms are up to 200 m to 300 m deep.

Proposed processes for the formation of lenticulae are plumes and convection in the ocean and plumes and convection within the ice shell, melt throughs, or cryovolcanism.

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