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In Gale Crater near Mars equator, dunes and ripples of sand, as well as
ground patterns locally stand out from the general lack of order of the rocky
terrain. In addition, images from Curiosity, the Mars Science Laboratory rover,
reveal more subtle orderly forms: widespread, meter-scale domains of evenly
spaced rock fragments (known as clasts) on sand in scattered locations. Here,
we examine quantitatively several clast domains on Mars and Earth, and compare
their geometry with those of random points. The clast distributions are not
only more orderly than expected by chance; they are hyperuniform, a
self-organized state recently recognized in diverse active materials and
biological systems but that appears novel for planetary surfaces. Using
numerical simulations, we show that clast displacements induced by gravity,
combined with changes of sand surface topography caused by aeolian sand
transport and ripple migration, can produce hyperuniform clast distributions
like those observed.
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