The core of Mars is completely liquid!

A few months ago, in December 2022, the Inside lander was breathing its last breath, unable to recharge its battery and its solar panels completely covered in dust. But the analysis of countless data collected by this small seismic station placed on the surface of Mars since November 2018 has not been interrupted, on the contrary!

Thanks to the analysis of seismic waves recorded by the instrument, we now know the internal structure of the Red Planet better. Insight data, particularly data collected during a strong meteorite impact in December 2021, have made it possible to more clearly establish the structure of the Martian crust on a large scale. But these data made it possible to explore the depths beyond the Martian crust. For the first time, seismic waves have been recorded through the core, allowing an unprecedented exploration of the planet’s deepest levels. Conclusion: The core of Mars is mainly liquid and contains not only iron but also a significant fraction of sulfur and light elements. Observations that help us better understand the planet’s formation and evolution compared to Earth.

Listen to its distant tremors to picture the depths of Mars

To achieve this, not one, but two seismic events were used. For seismic waves to travel through the epicenter, the events must occur far away from the seismic station and be large enough to be detected by seismometers. A much longer period than expected fortunately allowed the recording of two cases presenting these conditions. The first (S0976a) was a magnitude 4.2 earthquake. The second (S1000a) corresponds to a meteorite impact. Its magnitude is estimated at 4.1. The centers of both events were located in opposite hemispheres from InSight.

In both cases, the seismometer was able to detect the arrival of so-called SKS waves. However, these types of seismic waves are well known on Earth. They are what made it possible to discover the liquid nature of Earth’s outer core. S waves are actually shear waves. In fact, they cannot propagate in liquid media. But SKS waves represent shear waves in the mantle and pressure waves in the fluid core before reemerging as S waves.

A completely fluid core?

Also, unlike Earth, which has a liquid outer core and a solid inner core, Mars’ core is predominantly, if not entirely, liquid. ” At this time, we have not collected any clues indicating the presence of a solid seed in the heart of Mars. “, explains Jessica Irving of the University of Bristol, first author of the study published in the journal PNAS. ” We currently have only two seismic events, which do not allow us to image the exact core of the planet. It could be the smallest solid core we can’t see yet because of seismic signals. Seismic data, however, suggest that if the planet had a solid seed, it would have a radius of less than 750 kilometers (compared to 1,221 kilometers for Earth) and a liquid core thickness of 1,799 to 1,814 kilometers (compared to 2,300 kilometers for Earth). The liquid nature of the Martian core has been proposed before, but the new results suggest that it may be slightly smaller than previously thought. It may be a little denser than previous studies have suggested. The speed of propagation of seismic waves depends on the density of the medium, which is intrinsically linked to its composition.

A very different composition of the Earth’s core

The velocity of the seismic waves, as they pass through the core, is that it is not made of liquid iron, but contains a considerable amount of light elements, especially sulfur, as well as small amounts of oxygen, carbon, and hydrogen. The fraction of light elements in the core of Mars is twice that of the outer core of Earth. This combination could explain the absence of a particularly solid core,” Light elements lower the temperature at which the core can maintain itself in a completely liquid state ” says Jessica Irving.

These differences in the composition and structure of the core between Earth and Mars lead to a better understanding of the internal formation of the planets of the Solar System. It is indeed possible that planets located far from the center of the original solar nebula, such as Mars, incorporated more light-evaporating elements at the time of their formation. ” However, a more precise determination of the amounts of these elements is necessary to better understand that the differences between Earth and Mars result from material accumulated during their formation and are linked to the physical processes at play during planetary differentiation. “, explain the authors in the study.

An impact on the Martian magnetic field

The difference in internal structure between the two planets may play a role in the habitability of both worlds. While on Earth, the existence of a solid inner core and a liquid outer core allowed the establishment of a magnetic field, which permanently protected the planet’s surface from the damaging effects of the solar wind and allowed it to retain its water. Mars would not have been favorable. However, the planet had a magnetic field in its youth, before it gradually declined, making Mars inhospitable to life. This evolution may be related to the entire fluid structure of the fetus.

The data collected by Insight is continuously analyzed. ” Seismic records can contain much more informationJessica Irving adds. Combined with other scientific results, such as new measurements of the properties of iron alloys under high pressure and temperature, the conditions for the formation of Mars and other planets in the Solar System can be better controlled. »