Tracks of dust devils spotted from space.

Scientists scanning satellite images of the southern Sahara have detected trails left on the landscape by the whirlwinds commonly known as dust devils, the first such observations made from Earth orbit.

Cameras on several spacecraft that have landed on Mars have spotted such whirlwinds, and some images of the Red Planet from orbit show shadows cast by dust-filled funnel clouds, says Angelo Pio Rossi of the International Research School of Planetary Sciences in Pescara, Italy.

When Rossi and his colleague Lucia Marinangeli looked at satellite photos of Earth for similar tracks, they found them on images of central Niger. Several shots taken between 2000 and 2002 show traces that average a few dozen meters wide and 3 kilometers long. The trails aren't aligned with prevailing winds, so they probably aren't small drifts of dust. Repeated images of the same locale at different times suggest that the tracks last, at most, only a few weeks. That makes sense, the researchers say, because dust devils tend to scour only a thin layer of material from Earth's surface.

That's why the tracks probably aren't exposed dark soil, which lies at least several centimeters beneath the sand in that region, the researcher say. Instead, they suggest that the windswept tracks reflect less sunlight than normal because the dust devils whisk away oust and small sand grains.

The findings appear in the March 28 Geophysical Research Letters.