Seismic data from InSight show Mars has a solid inner core enveloped by a liquid outer core
Chinese-led analysis of more than 1,300 marsquakes suggests the red planet’s heart is a small solid iron‑nickel core surrounded by molten metal
Scientists report that Mars possesses a solid inner core surrounded by a liquid outer core, based on seismic data collected by NASA’s InSight lander.
A Chinese-led research team reached the conclusion after analyzing more than 1,300 marsquakes recorded by InSight between the spacecraft’s 2018 touchdown on a broad equatorial plain and its shutdown in 2022. The findings, published Wednesday in the journal Nature, indicate that the Martian inner core extends to a radius of roughly 380 miles (613 kilometers) and is encased by a molten outer layer that reaches as far as about 1,100 miles (1,800 kilometers) from the planet’s center.
The team inferred the core structure by examining how seismic waves from marsquakes propagated through the planet. Differences in wave speeds and conversions at boundaries inside Mars allowed researchers to distinguish solid from liquid layers, a method commonly used in studies of Earth's interior. Previous studies of Martian structure had suggested a largely liquid interior; the new analysis supports a small solid inner core encased by a larger liquid outer core.
The researchers described the inner core as likely composed primarily of iron and nickel, similar to Earth’s, but possibly enriched with lighter elements such as oxygen. The presence of a solid inner core alongside a liquid outer core is consistent with a process of inner-core crystallization that may have occurred in the past and could still be ongoing, the team said in the paper.
Determining Mars’ internal structure informs models of the planet’s thermal evolution and its ancient magnetic history. Mars currently lacks a global magnetic field, although remnant magnetism in portions of the crust shows that a planetary dynamo once operated. A solidifying inner core and molten outer core are relevant to theories about how and when that dynamo might have been sustained and why it eventually ceased.
InSight, a lander designed to study the Martian interior, recorded seismic activity across a range of magnitudes and depths before contact ended in 2022. The mission’s seismic catalogue provided an unprecedented dataset for probing Mars’ deep interior and has enabled multiple teams to refine estimates of the planet’s size, composition and internal layering.
The Nature paper presents one of the most detailed seismic assessments of Mars to date and narrows uncertainties about the planet’s core dimensions. The authors emphasize that continued analysis of InSight’s dataset, together with future seismic measurements and spacecraft missions, will further refine understanding of Mars’ interior and its geological history.
The new results align Mars more closely with Earth in terms of core structure while underscoring differences in scale and evolution. Mars’ inner core, at roughly one-fifth the radius of Earth’s inner core, reflects the red planet’s smaller size and distinct thermal path since formation. The study provides a clearer picture of how solidification and internal heat loss may have shaped Mars’ long-term geologic and magnetic development.