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S122a is the most significant earthquake, so far recorded on Mars. It had a magnitude of 4.7, moderate-sized by Earth standards, but caused enough vibrations to reverberate through the planet for at least six hours, which were recorded by NASA’s InSight lander on May 4, 2022. Because its seismic signal was similar to previous quakes known to be caused by meteoroid impacts, scientists who were analysing the quake thought such an impact may have been responsible here as well. They even launched an international search for a crater that ought to have resulted from the impact. It was perhaps the first time that all missions in orbit around Mars collaborated on a single project. However, an investigation, which stretched for many months and even included Mangalyaan, of the Indian Space Research Organisation (ISRO), failed to find any evidence for such a meteor. This led the scientists to conclude that the quake may have been caused by stresses that had built up in the Martian crest. Mars has no oceans so the movement of plates, or plate tectonics, is ruled out as a potential cause.
InSight was a NASA mission dedicated to the study of the Martian interior through geophysics, especially seismological events. During its time on Mars, InSight recorded over 1,300 ‘marsquake’ events. Of these, at least eight were from meteoroid impact events. The largest two formed craters around 150m in diameter. If the S1222a event was formed by an impact, the crater ought to have been at least 300m in diameter.
