Unveiling Mars' Subsurface Enigmas: Revised Findings from NASA’s InSight Lander Illuminate the Planet's Liquid Layers

An illustrative representation of Mars’ inner structure depicts the spread of waves from a meteorite impact in September 2021, as recorded by the SEIS seismometer onboard NASA’s InSight mission. The waves traverse the wholly liquid section of the silicate layer located at the mantle’s foundation, characterized by reduced seismic speeds. Credit: IPGP / CNES / N. Starter

New evidence contradicts earlier conclusions from NASA’s InSight Mars Lander about the planet’s internal architecture. Scientists have identified a liquid silicate layer at the base of Mars’ mantle, which implies a more compact and denser core than formerly calculated.

Initial results from NASA’s InSight mission enabled researchers to ascertain the inner structure of Mars, as detailed in scientific papers released in the summer of 2021. However, an analysis of fresh data, spawned by a significant meteorite collision on September 18, 2021, has called into question these original assessments of Mars’ inner composition.

The investigation into the wave propagation times caused by this impact involved a multinational consortium led by Henri Samuel, a CNRS researcher at the Paris Institute of Globe Physics. The team also included experts from CNRS, ISAE-SUPAERO, and Université Paris Cité, supported by CNES and ANR, along with collaborators from the Royal Observatory of Belgium, Universities of Maryland and Bristol, the Zürich Polytechnic School, the Russian Academy of Sciences, and NASA’s Jet Propulsion Laboratory. Their work revealed a liquid silicate layer at the mantle’s base, covering the metallic core.

Table of Contents

The Evolutionary Path of Mars

The revised model of this structure, published today, October 25, 2023, in the journal Nature, not only aligns more closely with all extant geophysical data but also provides a more accurate account of Mars’ developmental history.

Specifically, the newfound layering of Mars’ mantle clarifies the previously unexplained slow movement of diffracted waves generated by the September 2021 meteorite impact. These waves traverse the completely liquid section of the basal layer where seismic velocities are diminished.

Additionally, for numerous past seismic events, wave arrival times registered on Mars’ surface are consistent with reflections occurring at the upper part of this liquid layer—several tens of kilometers above the core—rather than at the core-mantle boundary as initially presumed.

Finally, the identification of this basal layer aids in understanding the orbit of Phobos, Mars’ nearest moon. The upper, semi-liquid portion of the basal layer effectively absorbs deformations instigated by the gravitational pull of Phobos. In contrast, the solid mantle above is more resistant and poorly attenuating of seismic activity, as evidenced by low-magnitude seismic waves detected on Mars’ surface.

Reassessing the Core of Mars

The discovery of this liquid layer necessitates a reassessment of Mars’ core dimensions and density. The newly proposed metallic core is 150 to 170 km smaller in radius (i.e., a radius of 1650±20 km) and 5 to 8% denser (i.e., 6.5 g/cm3) than what earlier seismic data indicated. This leads to the conclusion that the core comprises an alloy that contains fewer light elements, aligning more closely with cosmochemical data derived from Martian meteorites and high-pressure laboratory tests.

The researchers speculate that Mars likely underwent an early stage characterized by a magma ocean, the crystallization of which formed a stable, iron and radioactive element-rich layer at the mantle’s base. The heat from these elements then generated the aforementioned liquid silicate layer, surmounting the core.

Implications for Mars’ Thermal and Magnetic Characteristics

According to the study, the layered structure of the mantle acts as an insulator for the metallic core, preventing it from cooling and thus inhibiting the generation of a thermal dynamo. Henri Samuel elaborates that external forces would be necessary to explain the magnetic fields documented in Mars’ crust during its initial 500-800 million years. These forces could be energetic impacts or core movements triggered by gravitational interactions with now-extinct ancient satellites.

Contrasting Mars with Earth

The newly discovered layered internal structure of Mars’ mantle significantly diverges from Earth’s, indicating divergent evolutionary paths for these planets. Mélanie Drilleau, a research engineer at ISAE-SUPAERO and co-author of the study, states that this revelation “opens up new avenues for research, as seismic data recorded by InSight’s SEIS instrument will now be re-evaluated in the context of this groundbreaking paradigm.”

Reference and Acknowledgments

The findings are reported in an article titled “Geophysical evidence for an enriched molten silicate layer above Mars’ core,” published on October 25, 2023, in Nature. DOI: 10.1038/s41586-023-06601-8

NASA’s InSight mission concluded its operations in December 2022 after more than four years of unique scientific data collection on Mars.

The mission was managed by JPL for NASA’s Science Mission Directorate and was part of NASA’s Discovery program, overseen by the Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space constructed the InSight probe and was responsible for mission operations. CNES acted as the primary contractor for SEIS, with scientific responsibility assumed by the Paris Institute of Globe Physics (Université Paris Cité/IPGP/CNRS). CNES also funded the French contributions and coordinated the international consortium, which was involved in the integration, testing, and supply of the complete instrument to NASA. IPGP designed the VBB sensors and contributed to their operation on Mars.

Additional operational activities and data management for SEIS and APSS were handled by CNES in collaboration with the Centro de Astrobiologia (Spain). Data formatting and distribution were performed by IPG Paris’ Mars SEIS Data Service.

Other CNRS laboratories also contributed to the InSight mission’s data analysis, supported by CNES and the National Research Agency as part of the ANR MArs Geophysical InSight (MAGIS) project. These labs collaborated with IPGP and ISAE-SUPAERO and include LMD, LPG, IRAP, LGL-TPE, IMPMC, and LAGRANGE. They were also in collaboration with SODERN, JPL, ETH Zurich, the Max Planck Institute for Solar System Research, Imperial College London, and the University of Oxford.

Frequently Asked Questions (FAQs) about Mars’ internal structure

What new findings have been made about Mars’ internal structure?

Researchers have discovered a molten silicate layer at the base of the Martian mantle, which suggests that Mars has a denser and smaller metallic core than previously estimated.

Who led the international research team studying these findings?

The international research team was led by Henri Samuel, a CNRS researcher at the Paris Institute of Globe Physics. The team included scientists from various organizations such as CNRS, ISAE-SUPAERO, Université Paris Cité, and NASA’s Jet Propulsion Laboratory.

How was the data for this research obtained?

The data was obtained through the study of seismic waves generated by a powerful meteorite impact on Mars that occurred on September 18, 2021. The analysis was facilitated by the SEIS seismometer of the NASA InSight mission.

How does this new model differ from previous estimates?

The new model suggests a metallic core that is 150 to 170 km smaller and 5 to 8% denser than previously estimated. It also indicates that the Martian mantle is stratified with a molten silicate layer at its base.

What are the implications of these findings for our understanding of Mars?

The findings imply a different thermal and magnetic evolution for Mars compared to previous models. They also shed light on the observed trajectory of Phobos, Mars’s closest moon, and suggest that external sources are necessary to generate Mars’ early magnetic field.

What is the publication date and source of this new research?

The research was published on October 25, 2023, in the journal Nature.

When did NASA’s InSight mission end?

NASA’s InSight mission officially concluded in December 2022 after more than four years of collecting unique scientific data on Mars.

Who managed and supported the InSight mission?

The InSight mission was managed by JPL on behalf of NASA’s Science Mission Directorate. Lockheed Martin Space built the InSight probe and supported its operation. CNES was the prime contractor for the SEIS instrument and coordinated the international consortium involved in the research.

Are there future research plans based on these new findings?

While the text does not explicitly mention future research plans, the discovery of the molten silicate layer and its implications for Mars’ internal structure are likely to open new avenues for geophysical research and reevaluation of existing seismic data.

Unveiling Mars’ Subsurface Enigmas: Revised Findings from NASA’s InSight Lander Illuminate the Planet’s Liquid Layers