SciTechDaily
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Although the photo above isn’t new (it was captured by the High-Resolution Imaging Science Experiment (HiRISE), on the Mars Reconnaissance Orbiter on September 8, 2021), NASA just posted it to Instagram this week. The stunning image went viral, with some saying that it looked like an alien footprint.
You’re looking at 0° longitude on Mars—the Greenwich Observatory equivalent on the Red Planet. The Greenwich Observatory marks Earth’s Prime Meridian, which is a north-south line that defines where east meets west, and is used as the zero-reference line for astronomical observations.