On 26 November 2018, the NASA InSight lander successfully set down on Mars in the Elysium Planitia region. Seventy Martian days later, the mission’s seismometer SEIS began recording the planet’s vibrations. A team of researchers and engineers at ETH Zurich, led by ETH Professor Domenico Giardini, had delivered the SEIS control electronics and is responsible for the Marsquake Service. The latter is in charge for the daily interpretation of the data transmitted from Mars, in collaboration with the Swiss Seismological Service at ETH Zurich. Now, the journal Nature Geoscience published a series of articles on the results of the mission in the first months of operation on Mars.
As reported in these articles, InSight recorded 174 events until the end of September 2019. Since then, the measurements have continued leading to more than 450 observed marsquakes as of today, which have not yet been analysed in detail. This accounts for one event a day on average.
The data allows researchers observing how seismic waves travel through the planet and unveiling its internal characteristics – similar to how x-rays are used in medical tomography. Before InSight landed, researchers had developed a wide range of possible models to represent the internal structure of the red planet. The recorded marsquakes, already after few months, enable refining the understanding of the structure of the planet and to reduce the uncertainties.
Interpreting marsquake data is challenging
Marsquakes are similar to the seismic events we see on Earth, although they are generally of smaller magnitude. The 174 registered marsquakes can be categorized in two families: One includes 24 low-frequency events with magnitudes between 3 and 4, as documented in the papers, with waves propagating through the Martian mantle. A second family of marsquakes comprises 150 events with smaller magnitudes, shallower hypocentral depth and high frequency waves trapped in the Martian crust.
“Marsquakes have characteristics already observed on the Moon during the Apollo era, with a long signal duration (10 to 20 minutes) due to the scattering properties of the Martian crust”, explains ETH Professor Giardini. In general, however, he says, interpreting marsquake data is very challenging and in most cases, it is only possible to identify the distance but not the direction from which the waves are arriving.
