WORLD NEWS
Mars’ southern mantle could be 200-400°C warmer than its north, gravity shows asymmetry in the planet’s interior
Analysis suggests that the mantle beneath Mars’ southern highlands could be about 200 to 400°C warmer than beneath its northern lowlands. The researchers estimated the north-south asymmetry of the planet’s interior by looking for subtle seasonal gravitational signals in data that tracked three Mars orbiters for 16 years.
This is not the result of a direct measurement by inserting a thermometer into the ground on Mars. It is a tidal tomography model that links changes in gravity and rock hardness, and the exact size and cause of the temperature difference are not yet confirmed: a giant impact, mantle convection, or insulation by thick crust.
How to read the invisible interior of Mars
Mars orbits the Sun approximately once every 687 days and has a slightly distorted orbit. The sun’s gravity deforms Mars slightly depending on the season, and its response depends on how rigid and uniform the planet’s interior is. The researchers called the method of using these small changes to reconstruct lateral differences inside the planet “tidal tomography.”
What data were used, and for how long?
The researchers combined radio tracking data from Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter. The analysis used minute changes in the orbiters’ speeds measured by Earth’s deep space communication network, and the total observation period was 16 years. The gravitational effect created by atmospheric mass movement was also calculated separately in the model.
What does the 200–400°C difference compare?
This figure is not the Martian surface temperature, but rather an estimate of the north-south temperature difference representative of the mantle at a depth of approximately 50 to 1560 km. The observed gravitational signal could be explained only if the mantle’s effective shear modulus, or the property of resisting torsion, differed by more than 20% depending on location. The researchers calculated that during Mars’ long seasonal cycle, rock hardness becomes so sensitive to temperature that differences of 200 to 400°C could account for the dominant signal.
Why might it be warmer in the south?
The southern hemisphere of Mars has elevated ancient highlands, while the northern hemisphere has many low, flat lands. The thicker crust to the south may have trapped heat like a blanket, or lopsided mantle convection may have lingered. There is an explanation that a giant impact long ago created the north-south difference, but it is impossible to choose between the three based on this data alone.
What will this result change and what will we see next?
The fact that not only Mars’ external appearance but also its interior can vary from north to south is a clue to explaining the history of highlands and lowlands, ancient watery environments, and crustal magnetization. However, this is not evidence that a volcanic eruption is imminent or that there is life. With dedicated gravity missions, more seismic data, and rock composition from different regions, the effects of temperature and iron content can be disentangled more precisely.