Titan has the perfect name: With a diameter of 5150 kilometers, not only is it Saturn's largest moon but it also surpasses Mercury and Pluto. Unfortunately, Titan's atmosphere is thicker than ours and contains orange haze that shrouds its surface (inset). Now, the Cassini spacecraft, orbiting Saturn, has used radar to measure the moon's heights and depths. In the July issue of the journal Icarus, planetary scientists present the first global topographic map of the distant world. In the main image, north is up and south is down; red and orange represent Titan's highest altitudes, blue and green its lowest. Whereas Earth's tallest mountain towers nearly 9 kilometers above sea level, Titan's topographic variations are mild: Its highest point is just half a kilometer above the mean and its lowest just 1.7 kilometers below, perhaps because Titan's crust isn't strong enough to support tall mountains or because its thick atmosphere unleashes methane rains that erode them away.
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