  In Gale Crater near Mars' equator, dunes and ripples of sand stand out from
the general orderless, rocky terrain. In addition, images from Curiosity, the
Mars Science Laboratory rover, reveal more subtle orderly forms: widespread,
meter-scale domains of evenly spaced, pebble-size rocks (termed clasts) on
wind-blown sand in scattered locations. Here, we examine quantitatively several
clast domains on both Mars and Earth, and compare their geometry with that of
random points. The clast distributions are more orderly than expected by
chance; they differ significantlty from those associated with uniform (Poisson)
random processes. Moreover, they are hyperuniform, a self-organized state
recently recognized in diverse active materials and biological systems but that
appears novel for planetary surfaces. These patches are often surrounded by
recent wind-borne ripples, suggesting an interplay between sand transport,
ripple activity and clasts. Using numerical simulations, we show that clast
displacements induced by gravity, combined with the evolution of the sand
surface caused by aeolian sand transport and ripple migration, can produce
realistic hyperuniform and random clast distributions, as well as distinct
clast alignements. Our findings highlight the existence of easily overlooked
disordered hyperuniform states on ground surfaces, suggesting novel
self-organized states beyond distinct geometric patterns.
