Unveiling Mars’ Concealed Molten Layer: A Fresh Glimpse Beneath the Martian Mantle

An artist’s portrayal offers a glimpse into the interior structure of Mars, revealing a molten layer at the base of the mantle and above the core. The trajectory of seismic waves generated by a meteorite impact in September 2021, which diffracted along the Core-Mantle Boundary (CMB), is depicted by the purple line. The blue line illustrates the path of a seismic wave reflected at the upper boundary of the molten basal layer. Credit: IPGP / CNES / N. Starter

Recently, a team of scientists, actively engaged in NASA’s InSight mission, concluded an in-depth analysis of seismic data collected on Mars following a meteorite impact that occurred in September 2021. These findings herald a profound transformation in our understanding of the Red Planet’s internal composition and evolutionary history.

In light of these groundbreaking discoveries and prior geophysical observations, a study, co-authored by Attilio Rivoldini from the Royal Observatory of Belgium, has been published in the esteemed journal Nature. This study introduces a novel model for Mars’ internal structure, postulating a heterogeneous mantle encompassing a molten silicate layer above the liquid metal core.

Initial Insights and Assumptions

The initial results, rooted in data gathered during the InSight mission, have significantly enriched our comprehension of Mars’ internal configuration. By assuming a compositionally homogeneous and entirely solid mantle, these findings revealed a liquid metal core with an estimated radius of approximately 1830±40 kilometers and a relatively low density ranging from 6 to 6.2 g/cm³. Notably, the core exhibited a notable concentration of light elements. The determination of the core’s size relied on the detection of seismic waves that were reflected at a boundary known as the Core-Mantle Boundary (CMB), presumed to be the interface between the solid and liquid portions of Mars’ interior.

Reassessment Following a Recent Impact

Nonetheless, the landscape of our understanding shifted dramatically with the analysis of fresh data stemming from a powerful meteorite impact on September 18, 2021. An international consortium, under the leadership of Henri Samuel, a CNRS researcher at the Institute of Globe Physics in Paris, and featuring the involvement of Attilio Rivoldini from the Royal Observatory of Belgium, meticulously examined the propagation times of these seismic waves. Their analysis suggested the presence of a molten silicate layer at the base of Mars’ mantle, positioned above the metallic core, as a plausible explanation for the newfound data.

Consequently, this revelation gave birth to a revised structural model, unveiled on October 26 in the journal Nature. Notably, this model not only aligns more cohesively with the entirety of available geophysical data but also provides a more coherent narrative for Mars’ evolution since its inception.

Clarifying Seismic Oddities

The existence of a molten layer at the base of the mantle offers a compelling explanation for the previously unexplained sluggish propagation of seismic waves that diffracted along the CMB in September 2021. Furthermore, in the context of several prior seismic events, the arrival times of seismic waves appear to be compatible with reflections occurring at the upper boundary of the molten layer, situated several tens of kilometers above the metallic core, rather than at the CMB, as was previously assumed.

Implications for Core Dimensions and Composition

The presence of this molten layer at the base of the mantle has significant ramifications for our understanding of the size and composition of Mars’ metallic core. It suggests that the core’s radius is diminished by 150 to 170 kilometers (i.e., a radius of 1650±20 kilometers) in comparison to earlier estimations.

“At the same time, this smaller core is approximately 5 to 8% denser, measuring at 6.5 g/cm³. The fraction of light elements within the core appears to be less extensive than previously thought, aligning more closely with cosmochemical data derived from the analysis of Martian meteorites and high-pressure experiments,” elucidates Attilio Rivoldini.

Early Evolution of Mars

The authors of this comprehensive study propose a scenario in which Mars underwent an early stage marked by the presence of a magma ocean. The crystallization of this magma ocean subsequently generated a stable layer at the base of the mantle, characterized by a substantial enrichment of iron and radioactive elements. The heat emanating from radioactive decay played a pivotal role in establishing a molten silicate layer above the core.

For further insights on this study, consider exploring the following:

• NASA’s InSight Lander Unveils Mars’ Enigmatic Molten Layer
• Decoding the Mystery of Mars’ Core
• Scientists Unearth Molten Layer Concealing Martian Core

Reference: “Geophysical evidence for an enriched molten silicate layer above Mars’s core” authored by Henri Samuel, Mélanie Drilleau, Attilio Rivoldini, Zongbo Xu, Quancheng Huang, Raphaël F. Garcia, Vedran Lekić, Jessica C. E. Irving, James Badro, Philippe H. Lognonné, James A. D. Connolly, Taichi Kawamura, Tamara Gudkova, and William B. Banerdt, published on October 25, 2023, in Nature.
DOI: 10.1038/s41586-023-06601-8

About InSight and SEIS:

NASA’s InSight mission officially concluded in December 2022, following over four years of collecting invaluable scientific data on Mars.

The management of the InSight mission was overseen by JPL on behalf of NASA’s Science Mission Directorate. InSight formed an integral part of NASA’s Discovery program, administered by the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Lockheed Martin Space in Denver was responsible for constructing the InSight probe, inclusive of its cruise stage and lander, and provided operational support throughout the mission. CNES served as the primary contractor for SEIS (Seismic Experiment for Interior Structure), with scientific oversight falling under the Paris Institute of Globe Physics (Université Paris Cité/IPGP/CNRS). CNES also funded the French contributions, coordinated the international consortium, and oversaw the integration, testing, and supply of the complete instrument to NASA. IPGP took charge of designing the VBB (Very Broad Band) sensors, conducted pre-delivery testing, and contributed to the operation of VBBs on Mars.

The operations of SEIS and APSS (Auxiliary Payload Sensor Subsystem) were conducted by CNES as part of FOCSE-SISMOC, with support from the Centro de Astrobiologia in Spain. SEIS data are meticulously formatted and disseminated through the Mars SEIS Data Service of IPG Paris, forming part of the National Observation Service InSight, in which LPG (Laboratoire de Planétologie et Géodynamique), among others, also plays a role. The identification of daily earthquakes on Mars was carried out by InSight’s Mars Quake Service, a collaborative operational service led by ETH Zurich, featuring the participation of seismologists from IPG Paris, the University of Bristol (UK), and Imperial College London (UK).

Numerous CNRS (Centre National de la Recherche Scientifique) laboratories, including LMD, LPG, IRAP, LGL-TPE, IMPMC, and LAGRANGE

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