translated from Spanish: The internal structure of Mars revealed thanks to its seismic movements

The internal structure of Mars has been studied through a series of seismic movements recorded on the planet, which have allowed an estimate of the size of the nucleus, the thickness and structure of the crust and the mantle, according to a series of articles published today by Science.Los estudios, of an international collaboration with the participation of the Spanish Consejo Superior de Investigaciones Científicas (CSIC) , are an important step in understanding the formation and evolution of the planet. The investigations are based on the seismic signals of a dozen “marsmotos” collected by the SEIS seismometer of the INSight mission of the US agency NASA, a lander that arrived on Mars in 2018 to drill its surface. This is the first exploration by seismology of the internal structure of a telluric planet different from earth and the first time that direct measurements are obtained, explains To Efe Martin Schimmel, researcher of the Geociencias Barcelona (GEO3BCN-CSIC) who participated in two of the studies. These direct measurements – he points out – are fundamental to determine its internal structure and its geological and geochemical evolution. In addition, they serve to narrow down the large number of existing models that explain the evolution of Mars to its current state and can help to understand that of the Earth and the Solar System.Mars, according to the new data, would have a liquid core with an estimated radius of between 1,790 and 1,870 kilometers, a size that suggests the presence of light elements , such as sulfur, oxygen or hydrogen, inside, which would consist mainly of iron and nickel. The size of the core and the inner structure of the planet is also important in mantle convection processes that manifest on the surface, such as volcanic and tectonic activity. The thickness and structure of the crust is the subject of the second study, coordinated by the Paris Institute of Physics of the Globe (IPGP), with which Schimmel collaborates, in which the behavior of seismic waves and environmental seismic noise below the InSight landing site is analyzed.At this point, the crust has two strata or discontinuities , the first at about ten kilometers deep and under this one of twenty kilometers, where “it is supposed to be the base of the crust”, explains the expert. In addition, there could be a third layer, less defined, at 39 kilometers, although for this the data are inconclusive, says Schimmel.” The seismic waves of an earthquake are like the echo we generate when we scream in the mountain. And it is the echoes of these waves, which are generated when they are reflected in the core or in the boundary between it and the mantle, that we look for in the signals thanks to their similarity with the direct waves of the marsmoto, “explains Philippe Lognonné, of the IPGP, in a statement. The deployment in early 2019 of the SEIS seismometer on the surface of Mars allowed to “hear” hundreds of seismic events, some of which occurred thousands of kilometers away. A dozen of them contained information about the deep structure of the planet. Schimmel adds that the study of that data was “a challenge, but also fascinating,” among other reasons because the mars tsunamis recorded so far are of lower intensity than on Earth.” We have not had earthquakes of magnitudes greater than four degrees” and it was not always possible to establish clearly the direction in which the waves were arriving. In addition, they could only count on a seismograph and they had to learn to differentiate everything that the device recorded to clean and filter the noise generated by the wind on the surface or the deformations linked to the sudden changes in temperature that occur on the planet. The expert highlights the importance of the Twins weather station, on board InSight, built and operated by the Spanish Astrobiology Center (INTA-CSIC).” When we see very weak signals we must be sure that it has not been due to a blow of wind that has moved parts of the lander”, for which it is very useful to know the weather conditions, because “they generate a good part of the environmental seismic noise”. Until now, the internal structure of Mars was little known, as the models were based on data taken by orbiting satellites and analysis of its surface, which indicated that the radius of the nucleus was between 1,400 and 2,000 kilometers and that the crust was between 30 and 100 kilometers thick.

Original source in Spanish