Analysis of 16 years of measurements from three orbiters has revealed a difference of about 200–400 degrees Celsius between the mantle of Mars' southern and northern hemispheres. The finding may explain differences in the surface, magnetism, and tremors of Mars.
כוכב הלכת Mars Divided into two very different halves not only on the surface, but probably also deep down. An international team of researchers has found that the mantle beneath Mars' southern highlands is about 200–400 degrees Celsius warmer than the mantle beneath the northern lowlands. The finding is based on tiny seasonal changes in the planet's gravitational field, measured over 16 years using three probes.
The study, published in the journal Nature, presents for the first time tomography of The face of Mars Through its changing response to the sun's tidal forces. The researchers call the method "Tidal tomography". Similar to medical tomography, which uses indirect measurements to reveal what's going on inside the body, the new method uses tiny deformations of the planet to map differences in the structure of the mantle.
Two different halves of the same planet
The difference between the north and south of Mars has been known for decades. Most of the northern hemisphere is covered in low, relatively smooth plains. In contrast, the southern hemisphere is higher, rough, ancient, and densely cratered. The crust in the south is also about 25 kilometers thick on average, assuming similar densities in the two regions.
This division is called the Martian crustal dichotomy. It is evident not only in the height and appearance of the surface, but also in the strength of the rocks' magnetism and the behavior of seismic waves. Martian tremors measured by the lander InSight It has already been suggested that seismic waves weaken more rapidly in the south, a phenomenon that could correspond to a warmer mantle.
There is still no consensus on how the dichotomy came about. One hypothesis is that a massive impact early in Mars' history excavated the vast basin of the northern lowlands or altered the structure of the southern lowlands. Another hypothesis attributes the difference to the movement of material in the mantle, which raised and thickened the crust in one hemisphere and lowered the crust in the other.
The new finding shows that the distribution seen on the surface surprisingly corresponds to a thermal distribution that is preserved at depth even today.
How to measure temperature deep inside Mars without a thermometer
The researchers didn't directly measure the temperature in the mantle. They analyzed radio tracking data from the dashes. Mars Global Surveyor, Mars Odyssey and-Mars Reconnaissance OrbiterNASA's Deep Space Network has measured tiny changes in spacecraft motion from Earth, and from these changes it is possible to reconstruct changes inThe gravitational field of Mars.
Mars' orbit around the Sun is more elliptical than Earth's, and its axis of rotation is tilted. Therefore, the strength of the Sun's pull and its direction relative to the planet vary over the course of a Martian year, which lasts 687 Earth days. These tidal forces distort Mars slightly, and the response to the deformation depends on the stiffness of the materials inside it.
On a spherical, uniform planet, seasonal variations in the gravitational field should follow a relatively simple pattern. However, the researchers found that some components of the changing field deviated by up to 300% from what would be expected for a symmetrical Mars. They also examined the effect of seasonal variations in the atmosphere, including the transfer of carbon dioxide between the atmosphere and the polar caps, and concluded that it did not explain the full signal.
The models that best fit the data included a difference of more than 20% in the effective stiffness of the mantle between different regions. Over long timescales, such as a Martian year, mantle rocks behave not only as a rigid solid but also as a material that can deform slowly. The hotter the rock, the softer it is, so the researchers translated the difference in stiffness into a temperature difference of about 200–400 degrees Celsius.
Not an ocean of magma
The difference found does not prove that there is an ocean of molten rock beneath southern Mars. According to the researchers, the data could also be explained by solid but hotter and softer rock. However, the high temperature may allow for partial melting and localized pockets of magma beneath the lithosphere.
If such pockets do exist, it is unclear why the southern plateaus do not show clear evidence of young volcanism. The researchers suggest that the thick southern crust and the compressive forces acting on it may stop the magma from reaching the surface. In that case, it would accumulate as magmatic intrusions within the crust, which would be difficult to detect in orbit photographs.
The situation is different in the Cerberus Fossae region of the northern lowlands, where evidence of relatively young volcanic and seismic activity has been found. There, the local stress field may allow magma to exploit cracks and rise to the surface.
Early damage, insulation or flow in the shell
The researchers offer several possible explanations for the origin of the thermal anomaly. One possibility is a large-scale flow in the mantle, in which hot material rises from beneath the south. Another possibility is that the thick crust of the southern highlands acts as an insulating layer, retaining the heat beneath it for billions of years. A higher concentration of radioactive elements in the crust could also add to the heating over time.
A giant impact alone is difficult to explain how a difference of hundreds of degrees was maintained for billions of years. However, a combined scenario is possible: an ancient impact created or strengthened the difference between the halves of Mars, and as a result, the thick crust in the south continued to isolate the mantle and preserve the anomaly to this day.
The models also found that the southern mantle may be up to 5% richer in iron than the northern one. However, the researchers conclude that different composition alone cannot explain the measured changes, and that temperature is likely the main factor.
A hint at the disappearing magnetic field
Mars does not currently have a global magnetic field like Earth, but large areas of the southern crust carry ancient magnetism. This is evidence that early in the planet's history a dynamo operated in its core, creating a magnetic field.
Thermal distribution may explain why the southern crust is more magnetized. Stronger heat flow beneath the south could have affected the cooling of the rocks and the time at which they dropped below the Curie temperature and acquired permanent magnetism. It is also possible that differences in heat flow between the core and the mantle may have strengthened the dynamo beneath the southern hemisphere in the past.
Thus, the anomaly measured today may be a remnant of processes that occurred more than four billion years ago, when Mars was a more active world, with a dense atmosphere and water on its surface.
What is the connection between water and the possibility of ancient life?
The northern lowlands have previously been proposed as the site of an ancient ocean. So understanding how the north-south divide formed is also important for reconstructing the history of water on Mars. If the dichotomy formed early, it could determine where basins accumulated, how water flowed, and which areas maintained conditions suitable for life.
The study does not show evidence of life or detect liquid water today. It provides another piece in the puzzle of Mars' evolution and the transition from a warmer, wetter world to the cold, dry planet we know today.
Next step: A dedicated gravity map for Mars
The current measurements were collected from missions not specifically designed to map the mantle in 3D. A dedicated gravity mission, similar to the GRAIL missions on the Moon or GRACE on Earth, would be able to measure the changes with higher precision and on shorter timescales.
Future electromagnetic measurements could also test whether the hot region contains isolated pockets of melting or a more continuous layer of molten material. The researchers note that tidal tomography could also be used in the future to study other bodies, including Ganymede, Mercury, Io and Enceladus – without the need to land seismometers on them.
Questions and Answers
Have 200–400 degrees been directly measured inside Mars?
No. The temperature difference was inferred from seasonal changes in the gravity field and models of the response of mantle rocks to tidal forces. Therefore, it is an estimate based on data and models, not a measurement using a heat sensor.
Does this mean that there is liquid magma beneath southern Mars?
Not necessarily. A warmer, softer mantle could explain the signal even without melting. The study allows for the existence of pockets of partial melting, but does not prove that they exist.
Why is the Southern Hemisphere warmer?
The cause is still unknown. Possibilities include a flow of hot material in the mantle, insulation by the thick southern crust, radioactive heating, or the long-term result of a giant impact that changed the structure of Mars.
Why is the discovery important for the search for life on Mars?
It helps to understand when and how the basins and topographic differences that influenced water flow and ancient climate were formed. The discovery is not direct evidence of life.
מקור
The scientific article in Nature, by Alexander Berne and colleagues, published August 26, 2026. The article and its images are distributed under license CC BY 4.0 License.
More on the subject on the science website
- A surprising discovery on Mars: a massive mantle plume is pushing the surface of Mars upwards
- News from inside Mars
- The Mars InSight spacecraft was successfully launched to explore the Martian soil.
- Meteor collides with Mars: Seismic waves shake the Red Planet
- Plasma waves increase Martian atmosphere loss
For the scientific article: Opening the scientific article
