Bending to a high-power telescope trained on the moon at the McDonald Observatory in the Davis Mountains of west Texas, specifically the terminator line that is the far reach of the sun’s light at this phase—waning Gibbous moon—the contrast of light and dark makes visible the rims and floors of uncountable impact craters. My companion and I can see the crater walls, the striated lines of some long past moment of chaos, the crusted lip of the crater’s edge where the force of that energy lifted and curled into a rift of moon rocks. The sun’s light on the lunar surface is so mesmerizing along that line, so utterly beautiful, that coming away from the eyepiece, all you can see is moon.

And yet those craters, as wild and deep and fantastic as they are, are little to speak of set beside the highest mountain in the solar system: Olympus Mons, on Mars. The mountain’s base covers an area the size of the state of Arizona, about 114,000 square miles. Its summit rises to nearly 85,000 feet off the Martian surface. By comparison, mighty Mount Rainier National Park covers an area of about 368 square miles, and Mount Everest stands at only 29,029 feet. Olympus Mons is a shield volcano, formed entirely by flowing lava, not unlike Manua Loa, one of the five volcanoes that makes up Hawaii, but 100 times larger—so large, in fact, that if you stood atop Olympus Mons, you wouldn’t know you were on a mountain.

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