Olympus Mons Hides Its Own Slope

Olympus Mons on Mars rises about 21.3 km above the Martian surface and sprawls roughly 600 km across, making it the tallest known planetary mountain in the solar system. Because its flanks average only about a 5% slope, the volcano climbs so gradually that the planet’s curvature hides the rise. An observer near the summit would not see a dramatic mountainside, because the slope stretches beyond the horizon only a few kilometers away.

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