Mars Interior Revealed by InSight Seismology: Lumpiness, Crust Dichotomy, and Mantle Patches

Overview

Astrum explains how NASA's InSight lander and its Seismic Experiment for Interior Structure (SEIS) opened a new window into Mars interior. By listening for marsquakes, SEIS provided unprecedented insights into the crust, mantle and core, and how thickness variations and ancient impacts shape the Red Planet today.

• InSight landed on Elysium Planitia in 2018 and deployed SEIS, the most sensitive seismometer on another world
• First martian quakes appeared in 2019 and the mission recorded more than a thousand events, revealing how seismic waves travel through Mars
• Seismic data narrowed the crust thickness to an average of about 24–72 km and mapped the mantle down to a 1560 km depth and a core roughly 1830 km in radius
• In addition to seismology, InSight carried a radio science experiment to probe Mars interior via rotational dynamics
• A 2025 Science paper shows the mantle is not uniform but lumpy, likely containing ancient debris from early solar system impacts

These findings are reshaping how scientists think about Mars and rocky planets beyond Earth.

Introduction: A Tiny Lander with a Giant Goal

NASA’s InSight mission marked a milestone in planetary science by combining a stationary lander with a highly sensitive seismometer to study the interior of Mars. The seed idea was simple but profound: if we could listen to Mars from the surface, we could infer what lies beneath, much as seismology does for Earth. InSight’s Seismic Experiment for Interior Structure (SEIS), built in part by the French space agency CNES, was designed to detect ground motions small enough to reveal how Mars’s crust, mantle and core differ from Earth and other rocky planets. The mission was because Mars preserves a largely undisturbed interior, offering a fossil-like record of planetary formation.

How Seismology Works on Mars

Seismic waves travel differently through materials of varying density and composition. Primary (P) waves move by compression and can pass through both solids and liquids, while secondary (S) waves move by shear and cannot travel through liquids. By analyzing how P and S waves change speed, bend, and reflect, scientists can reconstruct the planet’s internal layering. On Mars, the challenge was to translate these signals into a coherent picture of a smaller, cooler world with a crust, mantle, and core that diverge from Earth’s. SEIS’s extraordinary sensitivity was essential because Marsquakes can be subtler than many Earthquakes, and the data must be clean enough to extract interior properties from a quiet, geologically quiescent planet.

The InSight Era: A Quiet Planet with a Dynamic Interior

InSight touched down near the equator on 26 November 2018 on a flat plain chosen for stability. Its mission duration extended through 2022, during which it recorded thousands of seismic events, including a magnitude around 5 quake in 2022. The seismic data enabled researchers to estimate Mars crust thickness, which is variable across the planet, and to infer mantle depth and core size. In addition, InSight contributed to a high-precision rotation science experiment that helped constrain the interior’s mass distribution. The fusion of these datasets provided an unprecedented glimpse into the Red Planet’s interior structure and history.

Key Interior Structure Findings

• The crust thickness on Mars is variable, with estimates converging toward an average range of roughly 24 to 72 km depending on the method and location, far thinner in some regions than others.
• The mantle extends to roughly 1560 km beneath the crust, indicating Mars’s mantle is substantial even after billions of years of cooling.
• The Martian core radius is inferred to be about 1830 km, composed of iron, nickel, and sulfur, consistent with a differentiated interior that cooled substantially over time.
• The crustal dichotomy on Mars—thin crust in the north and thick crust in the south—remains a striking feature requiring further study to determine its origin.

The 2025 Breakthrough: Lumpiness in the Martian Mantle

In 2025 scientists published results in Science showing that Mars’ mantle is not smooth and uniform. Seismic waves slowed in distinct regions across the mantle, revealing a patchwork of material properties, temperatures, and structures. These anomalies likely trace back to early solar system events when giant impacts created debris that sank into the mantle and became trapped, forming a legacy pattern that persists to today. The lead author Constantinos Haralambous emphasized that the pattern is reminiscent of shattered glass, with large shards and many smaller fragments. This mantle lumpiness provides crucial clues about Mars’s formation and early evolution and could influence later volcanic activity and crust formation. The finding suggests that other tectonically quiet terrestrial planets may also harbor lumpy mantles, reshaping models of planetary interiors across the solar system and beyond.

Why This Matters: Habitability and Exoplanet Insight

Understanding how interiors drive a planet’s magnetic field, atmosphere, and surface water is key to assessing habitability. Mars offers a time capsule of early planetary development, and lumpiness in the mantle hints at complex formation histories, including late-stage accretion and giant impacts. These results refine how scientists model the transition from a molten world to a planet with a stable crust and potential volcanic activity. In a broader sense, they also provide a framework for interpreting interior structures of rocky exoplanets where direct seismology is not possible, guiding the search for worlds that might harbor life.

Future Directions: From Robotic Seismology to Exoplanetary Science

The InSight era demonstrates that robust seismology can reveal internal planetary architecture even in small, distant worlds. Future missions may deploy more capable landers or orbiters to refine crustal maps, mantle dynamics, and core composition. As technology advances, new remote sensing methods could be developed to infer exoplanet interiors from afar, potentially helping identify planets with Earth-like habitability signatures. The overarching message is clear: understanding planetary interiors is essential for understanding their histories, and InSight has shown that seismology is a powerful tool for unlocking those deep secrets.