The crater in the center of this HiRISE image determines where the zero length of Mars is, as the Greenwich Observatory for Earth does. Credit: NASA / JPL-Caltech / UArizona
Although the photo above is not new (it was taken by the Mars Reconnaissance Orbiter’s HiRISE science experiment on September 8, 2021), NASA just posted it on Instagram this week. The stunning image went viral, with some saying it looked like an alien footprint.
You are watching 0 ° longitude of Mars – the equivalent of the Greenwich Observatory on the Red Planet. The Greenwich Observatory marks the main meridian of the Earth, which is a north-south line that determines where east meets west and is used as a zero reference line for astronomical observations.
When we reduce it a bit, we see that the Airy-0 crater is a wider context. Credit: NASA / JPL-Caltech / UArizona
The larger crater in this crater, called the Airy Crater, originally defined zero length for Mars, but as higher-resolution images became available, a smaller feature was needed. This crater, called Airy-0 (zero), was chosen because it does not need to correct existing maps.
Nowadays, the length of Mars is measured even more accurately with the help of radio-tracking landers such as InSight, but everything is still defined to keep the zero length at the center of this crater.
The full image shows more than the surroundings of the Airy-0 crater on Mars. Credit: NASA / JPL-Caltech / UArizona
This image was taken by the high-resolution scientific experiment (HiRISE) on the Mars orbiter. The map is designed here at a scale of 50 centimeters (19.7 inches) per pixel.
For a more recent image of stunning craters on Mars, see Martian Brain Freeze: Mars Express Reveals Utopia Planitia.
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