Two giant marsquakes rock Mars’ far side
NASA’s InSight lander touched down on Mars in November 2018 carrying the most sensitive seismometer ever designed. Since the mission’s arrival at the Red Planet, it has detected countless seismic events, dubbed marsquakes, using the signals to map the planet’s interior. But the two newly announced quakes, classified as S0976a and S1000a, were something special. “Not only are they the largest and most distant events by a considerable margin, S1000a has a spectrum and duration unlike any other event previously observed,” said Anna Horleston, a seismologist at the University of Bristol. “They truly are remarkable events in the Martian seismic catalogue.”
The first seismic event, S0976a, was of magnitude 4.2 and occurred on 25 August 2021, originating in Valles Marineris, a vast network of canyons that extends for 4,000 kilometres (2,500 miles) on the opposite side of the planet to InSight. Valles Marineris is what scientists call a graben system – a valley with distinct fault blocks that are relatively lower than the blocks on either side of them. The Martian canyon complex is one of the largest such systems in the entire Solar System. Although previous orbital imagery of Valles Marineris had identified the aftermath of seismic activity on Mars, such as faults and landslides, the 2021 detection is the first time an event has been recorded at this location. The second marsquake, S1000a, occurred 24 days later on 18 September 2021. This event was slightly smaller at magnitude 4.1. The second marsquake’s exact point of origin remains unknown, though scientists have isolated it to the far side of Mars. S1000a also lasted for 94 minutes – the longest seismic event ever recorded on Mars.