Diverse Patterns of Pebbles on Sand on Mars and Earth

Abstract On Mars, fields of sand dunes contrast with the generally cratered, rocky terrain commonly seen from orbit. Near the equator, in Gale Crater, images from the rover Curiosity also reveal order on smaller scales: ripples on dunes, and ground patterns in scattered sites. The patterns include relatively inconspicuous forms: evenly spaced pebble‐size rocks (here termed clasts) on meter‐scale domains of wind‐blown sand. Here, we examine quantitatively several such domains on both Mars and Earth. The clasts are significantly more orderly than expected by chance. Moreover, many are “hyperuniform,” a self‐organized state recently recognized in diverse active materials and biological systems but that appears novel for planetary surfaces. We use numerical simulations to examine how diverse clast distributions, ranging from random and hyperuniform dispersions to distinct alignments, can emerge spontaneously from clast displacements induced by gravity combined with the wind‐driven evolution of the surface, sand transport, and ripple migration. This paper highlights clast arrangements, often‐overlooked relative to more obvious ground patterns. Moreover, our methods and findings may have quantitative implications for issues of global significance on Earth and other planets, including dust emission from vast areas into the atmosphere, and planetary energy budgets.