Hop, skip and a jump
The bouncing grains of Martian sand
By Sid Perkins
The Martian atmosphere is thin, but it can whip up a mean sandstorm: On the Red Planet, wind-driven grains travel up to 10 times faster than those blowing along Earth’s surface, new analyses suggest.
As on Earth, most windblown sand grains on Mars get where they’re going by saltating, or repeatedly bouncing along the surface. On Mars, however, sand grains can hop higher than they do on Earth because gravity at the planet’s surface is much weaker than it is here on Earth, says Eric J.R. Parteli, a physicist at the Federal University of Ceará in Fortaleza, Brazil. That, in turn, stretches the length of each hop, a parameter that influences the spacing of ripples and other features on dunes, which are massive accumulations of tiny grains (SN: 10/19/02, p. 248).
Using a detailed model of turbulent winds, as well as data gathered by Mars rovers and satellites, Parteli and his colleagues analyzed how saltating sand grains behave on the Red Planet. Grains of Martian sand are made of basalt, which is denser than the quartz that makes up much of our planet’s sand, suggesting they wouldn’t bounce as high. However, the gravity at Mars’ surface is less than 40 percent that experienced at ground level on Earth.