Encyclopedia of the Solar System 2nd ed

Europa 441

FIGURE 13 Examples of chaos on Europa. (a) Conamara Chaos exhibits distinct plates of preexisting terrain (see also Fig. 14). (b)

Murias Chaos, a region of fine-textured chaos that has apparently overflowed its margins on one side, depressing the surrounding plains.

(c) The edge of Thrace Macula, showing fine-textured material and a hint of preexisting terrain within, suggesting that the preexisting

plains material has disaggregated in place. Dark plains material from Thrace has embayed the surrounding ridged plains, suggesting

that it was relatively fluid when it was emplaced. (After Prockter et al., 2004.)

as they rise to the surface, causing disaggregation into matrix
material and local flooding by dark, low-viscosity melt.

4.2.2 CHAOS

Chaos regions are areas in which kilometer-scale blocks of
existing ridged plains material have translated and rotated
with respect to one another within a mixed-albedo matrix
of hummocky material (Fig. 13). The matrix material can
be low-lying or high-standing relative to the surrounding
plains. In one area, Conamara Chaos, at least 60% of the

preexisting terrain has been replaced with or converted into

matrix material, and the matrix in part stands above the sur-

roundings. Some of the broken plates have been rotated

and/or moved by as much as several kilometers. These plates

can be reassembled like a jigsaw puzzle, reconstructing por-

tions of preexisting ridges and troughs (Fig. 14), although

much of the original surface has been destroyed.

Chaos regions have been interpreted as places where

Europa’s heat flow has been enhanced, and where local

melt-through of ocean water to the surface may have oc-

curred. In such a model, the blocks are analogous to

FIGURE 14 Broken plates of

material within the hummocky

matrix of Conamara Chaos (left) can

be reconstructed into their original

positions like a jigsaw puzzle, by

matching up older lineaments. This

exercise shows that the plates may

have moved by several kilometers

(arrows show approximate amount

of displacement), indicating that the

matrix material was originally

mobile. Most of the original terrain

is missing, however, and may have

been subsumed or disaggregated

during formation of the chaos.

(After Spaun et al., 1998.)