New exciting research, based on seismic data from NASA’s InSight mission, reveals that Mars’ mantle is far from smooth and homogeneous—instead, it resembles a “Rocky Road” brownie filled with compositional chunks up to 4 km wide. These fragments are remnants of Mars’ violent early history: colossal impacts that formed global magma oceans and deposited chemically distinct materials. As the planet cooled and its crust formed a rigid, immobile lid, these ancient mantle pieces became effectively sealed in place, preserving a geological record of Mars’ formative events that occurred during its first 100 million years, still detectable after more than 4.5 billion years.
https://www.jpl.nasa.gov/news/nasa-marsquake-data-reveals-lumpy-nature-of-red-planets-interior
Why this is surprising
When Mars formed, it should have melted inside from all the heat of impacts and radioactive decay, creating a global “magma ocean.” That molten phase ought to have smoothed everything out, erasing big blobs of material. Yet InSight’s data shows the lumps are still there—frozen in place for billions of years. This means Mars didn’t mix itself as thoroughly as scientists expected, or giant impacts later on stirred new chunks into the mantle. Either way, it makes Mars’ interior far messier—and more interesting—than the standard textbook picture.
Earth has its own mystery blobs
Deep inside our planet, seismologists have found two giant lumps at the base of the mantle—one under Africa and one beneath the Pacific. These shouldn’t really be there either, because Earth’s mantle is constantly stirred by plate tectonics and convection. Yet they’ve survived for billions of years. A 2023 study suggests they may actually be the buried remains of Theia, the protoplanet that smashed into Earth and gave rise to the Moon
(Yuan et al., 2023). Just like Mars, Earth may also carry fossil scars of its earliest, most violent days, only hidden much deeper down. Earth is larger than Mars and Theia is said to have been the size of Mars.
How can we tell that Mars has chunks inside?
When Marsquakes occur, they generate P-waves (compressional) and S-waves (shear) that travel through the planet. On a homogeneous planet, these waves would travel smoothly, with predictable speeds and arrival times. But when waves encounter heterogeneities — regions with different density, temperature, or composition, they scatter, reflect, or slow down.
InSight’s SEIS seismometer, sensitive enough to detect Mars quakes from the other side of the planet (!!!) collected over 4 years of data, with hundreds of events (from local quakes to meteorite impacts). The seismic waves arrived “smeared out” and scattered. When they modelled this, the scientists who published the study realised that the scattering could only be explained by the mantle being “lumpy”, filled with bodies up to up to 4 km across that have different seismic velocities from their surroundings. So InSight effectively measured how seismic waves were scrambled by these hidden structures in the mantle.
Insight working on Mars
What does it mean?
Was there life on Mars? Since David Bowie and other people who asked themselves the same question, humanity has been wondering. The more we learn about it, the more we realise that Mars (and Earth, and our Solar System) has a very interesting history, more interesting than we previously thought. How did Mars became the rusty, dusty planet that it is today? And would have, at some point, Mars had the conditions to create life? On Earth, wherever there is liquid water there is life. The oceans of water on Mars slowly started drying out about 3.2 billion years ago! Was it because of this giant impact? Was there a giant impact? If Mars had oceans does that mean that Mars had developed life?
The “Rocky Road” Mantle as a Fossil Record
The new InSight seismic analysis showing 4 km–scale heterogeneities in Mars’s mantle shows that Mars never fully mixed its interior after its magma-ocean phase. Unlike Earth, where plate tectonics, convection, and resurfacing recycle crust and mantle continuously, Mars quickly “froze” under a stagnant lid. That’s why those primordial fragments are still there, frozen time capsules from the planet’s first ~100 Myr. It’s geological memory on a planetary scale.
Atmospheric Loss and Magnetic Field Shutdown
The preservation of those chunks ties directly into why Mars lost its atmosphere. Early Mars did have a magnetic field, generated by a convecting liquid core, but evidence suggests it shut down by ~4.1–4.0 billion years ago. Without a magnetic shield, the solar wind directly interacted with the upper atmosphere, stripping it away over hundreds of millions of years (as MAVEN has beautifully measured).
The same stagnant-lid behaviour that preserved the mantle heterogeneity also doomed Mars: without vigorous convection or plate tectonics to keep its core dynamo going, the field collapsed. So the “fossilised” mantle and the atmospheric loss are two sides of the same coin, Mars cooled fast and locked itself in.
Impact Connections: Hellas, Alba Mons, and the Moons
- Hellas Basin (~2300 km wide) is one of the largest impact structures in the Solar System. On Earth, we’d expect such an impact to have erased mantle signatures through global mixing. On Mars, because the crust and mantle locked in early, the record of Hellas could still be preserved in both crustal thickness maps and compositional heterogeneity.
- Alba Mons, the largest volcano on Mars, nearly antipodal to Hellas (Zhang et al., 2022)(Williams & Greeley, 1994), , could be a surface expression of the impact’s shock-focusing effect, similar to how seismic waves from the Chicxulub impact may have influenced Deccan volcanism on Earth.
- Phobos and Deimos: One leading hypothesis is that a giant impact generated a debris disk around Mars that later coalesced into these moons. The Hellas-forming event is a good candidate in terms of scale, although some models suggest the Borealis Basin impact in the northern hemisphere was more directly responsible. Either way, the new mantle heterogeneity finding strengthens the view that Mars’s violent bombardment phase had system-wide consequences—core, crust, volcanism, and satellites.
The Bigger Picture
Mars is essentially a planetary time capsule:
- It preserves mantle fragments from its birth.
- It froze its crust early, retaining impact scars and chemical fingerprints.
- It lost its dynamo, exposing its atmosphere to the solar wind.
- It still carries moons that may be “living fossils” of those giant impacts. That we might be able to find out if is true or not sooner than we think, when the Martian Moons eXploration (MMX) robotic space probe, set for launch in 2026 will bring back the first samples from Mars’ largest moon Phobos.
Where Earth’s hyperactive geology erases its childhood, Mars wears its scars openly. We often think of Mars as similar to Earth. Also, if you send a robot to Mars, chances are it will still be there in twenty years and not lasting only four hours like on the surface of Venus. Mars is not too far either, so a trip there does not take years but months and finally, despite its orange looking sky, Mars is a place that when we look at, we can recognise, as scientist Ashwin Vasavada said. But just how much is Mars like Earth?
References and read more
Mantle Heterogeneity & Stagnant-Lid Evolution
Charalambous, C., Samuel, H., Stähler, S. C., Verhoeven, O., Bagheri, A., Drilleau, M., et al. (2025). Seismic evidence for kilometer-scale heterogeneities in the Martian mantle. Science.
NASA/JPL-Caltech. (2025, August 28). Mars’ mantle revealed as rocky road of colossal chunks [Press release].
Hellas Basin & Antipodal Alba Mons
Williams, D. A. (1994). Alba Patera and the northern Tharsis plains: Geologic history from impact basin to volcanic province. Icarus, 109(2), 288–303.
Zhang, C., Wang, H., & Xiao, L. (2022). Is Alba Patera the antipodal effect of Hellas basin? The Innovation, 3(8), 100268. (Models the Hellas–Alba Patera antipodal effect; finds Alba is ~2° (~119 km) from the theoretical antipode and explains it via early crustal properties/partial melt. Great figures.)
Crustal Dichotomy & Giant Impacts
Andrews-Hanna, J. C., Zuber, M. T., & Banerdt, W. B. (2008). The Borealis basin and the origin of the Martian crustal dichotomy. Nature, 453(7199), 1212–1215.
Ballantyne, G. M., Reese, C. C., & Collins, G. S. (2023). Revisiting giant impact models for the origin of the Martian crustal dichotomy. Icarus, 391, 115264.
Cheng, C., Zhu, M.-H., & Wünnemann, K. (2024). Formation of the Martian crustal dichotomy: Giant impact and subsequent evolution. Icarus, 406, 115720.,
Dynamo History & Magnetic Field
Hsieh, W.-P., Huang, S., & Zhang, J. (2024). Thermal conductivity of iron-sulfur alloys at core conditions: Implications for the Martian dynamo. Science Advances, 10(4), eadi6789.
Samuel, H., Stähler, S. C., Verhoeven, O., Bagheri, A., & Giardini, D. (2023). Structure and composition of Mars’ core and mantle revealed by InSight. Nature, 615(7953), 306–311.
Steele, L. J., Johnson, C. L., Mittelholz, A., Langlais, B., Oliveira, J. S., & Weiss, B. P. (2024). Weakly magnetized Martian basins and implications for a reversing dynamo. Nature Communications, 15(1), 5024.
Steele, L. J., Weiss, B. P., Mittelholz, A., & Johnson, C. L. (2023). Evidence for a long-lived Martian dynamo from meteorite paleomagnetism. Science Advances, 9(2), eade7335.
Atmospheric Escape
Dong, C., Jin, M., & Ma, Y. (2023). The evolution of Martian atmospheric escape under solar EUV radiation. Icarus, 394, 115301.
Jakosky, B. M., Brain, D., & Grebowsky, J. (2018). Loss of the Martian atmosphere to space: MAVEN results and integrated perspective. Icarus, 315, 146–157.
NASA Goddard / MAVEN Mission Team. (2025, April 16). MAVEN makes first direct observation of atmospheric sputtering at Mars [Press release].
Zhang, T. L., Guo, J., & Fang, X. (2025). Variability of ion escape from Mars under quiet solar wind conditions. Nature Communications, 16(1), 1712.
Phobos & Deimos Origins
Spectroscopically, both moons look a lot like carbon-rich asteroids or Jupiter’s Trojan companions — dark, primitive bodies that formed in the outer Solar System. For decades, that led many scientists to think they were captured asteroids. But there’s a catch: their orbits don’t behave like captured objects. Instead of being tilted, elongated, or chaotic, Phobos and Deimos move in nearly perfect circles right above Mars’ equator — something capture alone can’t explain. The simplest way to reconcile this puzzle is that the moons were born from material ejected off Mars itself. In this scenario, a giant impact blasted debris into orbit, which then coalesced into small moons. That’s why their orbits fit Mars so neatly, even if their surfaces still resemble asteroids
Kuramoto, K. (2024). The origin and evolution of Phobos and Deimos: Insights from theory and the MMX mission. Annual Review of Earth and Planetary Sciences, 52, 123–152.
Wargnier, Q., Rivkin, A. S., & Barucci, M. A. (2025). Compositional constraints on the origin of Phobos and Deimos. Astronomy & Astrophysics, 689, A10.
Hyodo, R., Genda, H., Charnoz, S., & Rosenblatt, P. (2019). On the impact origin of Phobos and Deimos: Implications for their compositions and dynamical evolution. Scientific Reports, 9, 19833.
Earth’s own lumps
California Institute of Technology. (2023, November 1). The remains of an ancient planet lie deep within Earth.
Yuan, Q., Li, M., Desch, S. J., Ko, B., Deng, H., Miyazaki, Y., Asimow, P. D., et al. (2023). Moon-forming impactor as a source of Earth’s basal mantle anomalies. Nature, 623, 95–99.