The first direct seismic observations from the InSight lander of the POT on Martian soil have been featured this week in the journal Science. The results provide key information on internal structure and the composition of Mars. The international team has analyzed data from a dozen ‘martemotos’ recorded by the ultrasensitive broadband seismometer SEIS (Seismic Experiment for Interior Structure), deployed by this mission.
Information about the interior of Mars
“These three studies provide important clues about the structure of Mars and they are also key to improving our understanding of how this planet formed billions of years ago and evolved over time, ”write the seismologists Sanne cottaar, from the University of Cambridge, and Paula Koelemeijer, from the Royal Holloway of the University of London (both in the UK), in a related opinion piece in the same journal.
The study and analysis of seismic data recorded by SEIS has allowed scientists to determine the thickness and structure of the crust of Mars. This is the focus of one of the studies, whose first author is Brigitte Knapmeyer-Endrun, geophysicist at the University of Cologne (Germany). In this work he has collaborated Martin Schimmel, researcher of Geosciences Barcelona (GEO3BCN-CSIC).
Thus, Knapmeyer-Endrun and his colleagues have used Martian earthquakes and ambient seismic noise to image the structure of the planet’s crust under the InSight landing site.
The team found evidence of a multi-layered crust, which could have two or three levels. Extrapolating these data to the entire planet, the researchers showed that the average thickness of the crust of Mars could be between 24 and 72 kilometers.
Measuring the thickness of the crust at the InSight landing site is sufficient to map the crust of the entire planet. Measurements made from satellites orbiting Mars provide a very clear picture of its gravitational field, allowing scientists to compare relative differences in crust thickness with measurements made at the landing site. “Combining these data provides an accurate map,” the researchers note.
“What seismology can measure is mainly speed contrasts. These are differences in the speed of propagation of seismic waves in different materials, ”says Knapmeyer-Endrun.
According to this geophysics, “in a very similar way to optics, we observe phenomena such as reflection and refraction. When it comes to the crust, we also benefit from the fact that the crust and the mantle are made up of different rocks, with a strong jump in speed between them. From these jumps, you can determine with great precision the crust structure”, He clarifies.
A statement issued by the University of Cologne highlights that the study of the crust of Mars is especially interesting because it was formed at an early stage from the remains of a molten mantle: “Data on its current structure also provide information on how Mars evolved. In addition to a more precise understanding of the red planet evolution, helps to decipher how the first differentiation processes developed in the solar system and why Mars, Earth and other planets are so different today ”.
Thick lithosphere and a liquid and metallic core
For its part, the team of Amir khan, from the Institute of Geophysics at ETH Zurich (Switzerland) and first author of another of the works, used the direct and reflected seismic waves on the surface of eight low-frequency Martian earthquakes to probe more deeply and reveal the structure of the mantle of Mars up to a depth of almost 800 km. Their findings indicate that there is a thick lithosphere at almost 500 km below the surface and that, like the Earth, possibly has a low velocity layer underneath.
Deeper still, Simon Stähler, a geophysicist in the Department of Earth Sciences at ETH Zurich, and his colleagues used the faint seismic signals reflected at the boundary between the core and the Martian mantle to investigate the Martian core. The GEO3BCN-CSIC researcher Martin Schimmel has also collaborated in this research.
The data suggest that the liquid core of Mars would have a radius of around 1,830 km (between 1,790 and 1,870 km). This size indicates, according to the authors, the presence of a series of light elements (such as sulfur, oxygen or hydrogen) inside, consisting mainly of iron Y nickel.
Schimmel comments that “the studies published today provide the first direct measurements of the inner layers of another planet. These data are key to determine its interior structure, as well as its geological and geochemical evolution ”. This researcher has been collaborating for some years in the development of seismic signal processing next to Eléonore Stutzmann, Zongbo Xu Y Philippe Lognonné, from the Institute du Physique du Globe in Paris (IPGP) and co-authors of the published works.
Thanks to the sensitivity of the SEIS instrument, scientists have been able to ‘hear’ seismic events that were happening thousands of kilometers away. The waves vary in speed and shape when they travel through the different materials that make up the interior of the planet, which has allowed seismologists to study the internal structure of the planet.
Thanks to the data recorded by the wind and temperature sensors of the TWINS Instrument incorporated in the InSight probe, developed by the Spanish Astrobiology Center (CAB, CSIC-INTA), the authors were able to verify that the seismic waves analyzed were either generated by vibrations produced by the wind.
The team of Mars Quake Service The mission was thus able to record and catalog a total of 600 seismic events, of which about 60 correspond to relatively distant so-called ‘martemotos’. A dozen contained information about the deep structure of the planet.
NASA’s InSight lander retracted its robotic arm on October 3, 2020, revealing the spot where the self-digging “mole” attempted to burrow into the planet’s surface. (Image: NASA / JPL-Caltech)
Riddles of the evolution of Mars
Schimmel points out that “knowing the size of the core of Mars and its structure provides information on how the magnetic field that once protected the planet’s atmosphere from high-energy particles from the sun could have been generated.”
In addition, the researcher emphasizes, the size of the nucleus and the interior structure of the planet play a key role in the convection processes of the mantle that are manifested on the surface, such as the volcanic and tectonic activity. “Understanding the evolution of Mars also helps to understand why the Earth evolved in a certain way and better understand our solar system,” he points out.
“Direct seismic observations on Mars represent a breakthrough in planetary seismology,” write Cottaar and Koelemeijer. “In the coming years, when more measurements of Martian earthquakes are obtained, scientists will refine these models of the red planet and reveal more enigmas of this planet,” they conclude.