October 1, 2002
Your birthday coincides with the eternal dance of celestial bodies — planets tracing their ancient orbits, moons rising and setting, comets...
Rectangular Ridges on Mars
Birthday · October 1, 2002
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APOD published October 1, 2002. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
What could cause rectangular ridges on Mars? As data flows in from the two spacecraft currently orbiting Mars, surface structures are seen that are not immediately understood. These structures pose puzzles that planetary geologists are eager to solve, as they might provide clues to past processes that have shaped Mars over billions of years. On the right of the above image is an unusual array of ridges first spotted in Mariner 9 data in 1972. A ridge wall runs for about 5 kilometers. Two competing progenitor theories include hardened sand dunes and once-molten rock that seeped through surface cracks and cooled. Dubbed "Inca City" for their resemblance to stone walls of an ancient Earth civilization, the new Mars Global Surveyor images now show them to be part of a larger circular pattern, indicating an origin possibly related to the impact crater. (Non-natural origin hypotheses are not invoked by conservative scientists unless clear indications exist that natural processes could not work.)