Deep in the Sahara Desert lies a crater. Nearly a perfect
circle, it is 1.9 kilometers (1.2 miles) wide, and sports a rim
100 meters (330 feet) high. The crater sits in a vast plain of
rocks so ancient they were deposited hundreds of millions of
years before the first dinosaurs walked the Earth. Modern
geologists long debated what caused this crater, some of them
favoring a volcano. But closer examination of the structure
revealed that the crater’s hardened “lava” was actually rock
that had melted from a meteorite impact. Advanced Spaceborne
Thermal Emission and Reflection Radiometer (ASTER) on NASA’s
Terra satellite captured this image of Tenoumer Crater in
Mauritania on January 24, 2008. In this simulated-true-color
image, the arid landscape appears in varying shades of brick
red, brown, and tan. The crater’s outline is unmistakable, yet
it doesn’t necessarily look like a crater; the light and shadows
make it look more as if someone pressed a giant cookie cutter
into the rock. In this image, the sunlight sh