Mars is kind of like Texas: things are just bigger thereRipples of sand sculpted by wind on the Martian surface soar higher than their terrestrial counterparts in relation to the distance between each one, a new study shows. While several conditions might contribute to the difference, observations of Mars are not yet fine enough to tell exactly what's going on.
These ripples, like small sand dunes, are common on Mars and are usually found in low-lying areas and inside craters. They can be 20 feet (6 meters) tall and form dramatic patterns.
Windblown sand also creates larger repeating dunes that resemble the Pacman gaming character, horseshoe crabs, and even a brain. Though some look almost sculpted by knowing hands, they are merely the result of wind doing constant battle with gravity. The details of their development are not understood.
The new study, by Kevin Williams of the Smithsonian National Air and Space Museum, shows that the heights of ripples are twice what typically occurs on Earth for ripples of a given separation.
Using pairs of images from NASA's Mars Global Surveyor to gain a stereo effect, it is the first study to pin down the heights of Martian ripples. Previous work has measured taller dunes.
In a telephone interview, Williams explained what might be happening.
Unlike regular sand dunes -- which on both planets can be taller than ripples -- the ripples on Mars might be composed of small pebbles moved along when hit by smaller windblown particles, Williams said. Since gravity is weaker than on Earth, Mars' strong winds might carry the particles farther, resulting in ripples with longer wavelengths. The conditions may also allow material to move higher up a developing slope.
"When particles are hit and jump into the air, they would travel further before falling," he said.
Because no spacecraft has ever investigated the grain size of particles in individual ripples, though, firm conclusions can't be drawn. Lower air density may also play a role.
Williams presented his findings Nov. 3 at the annual meeting of the Geological Society of America in Seattle.
Dunes on Earth can be exotic, too. And as with those on Mars, sometimes you have to back up a ways to see the remarkable patterns. A recent satellite image showed dunes in the Namib Desert in southwest Africa that are among the biggest in the world, nearly 1,000 feet (300 meters) tall.
Williams said some dunes on Mars might also approach that height.
A pair of NASA rovers en route to the red planet could answer some questions about the ripples, Williams said.
If one of the crafts lands near small ripples or larger dunes -- and that won't be known until after the landing -- it could be sent to inspect the size of particles or pebbles of which the features are composed. This would help scientists figure out how the things form and how the winds of Mars act over time.
This article is part of SPACE.com's weekly Mystery Monday series.
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