The stiffness contrast is what was measured; the temperature is an interpretation laid on top of it. Berne's team found the Martian mantle must differ in stiffness by more than 20 percent between hemispheres, rigid in the north and softer in the south [8]. Read as a springy, purely elastic response, that gap implies a north-south temperature difference above 1,000 degrees C, which Berne discards because the whole southern half would then be molten and visibly is not [9]. The published figure of 200 to 400 C instead assumes the tidal flexing creeps slowly across the Martian year rather than snapping back [10]. That substitution is doing a factor of 2.5 to 5 of work [11]. Anyone using the temperature number downstream is also buying the creep model.
The alignment is what changes the argument. Southern warmth on its own was already in circulation: a 2024 study of marsquakes recorded by InSight floated it to explain why seismic energy dies away faster in the south [13]. What the new simulations add is geometry, with the deep stiff-soft boundary tracing the surface boundary even where that line wanders north or south [12]. A crustal feature 25 kilometres deep in average thickness contrast [3] whose deep counterpart follows its wiggles is not easily read as damage done from outside.
Not easily, but not impossibly, and this is where the clean story stops. Phys.org, reporting the same paper, says the cause of the anomaly remains unclear and lists a giant impact releasing heat from the north alongside past spontaneous convection in the southern mantle and thick geological features trapping heat [19]. Depth does not kill the impact hypothesis. It hands it a worse exam question: why an impact-generated thermal anomaly would still be registered against the topographic boundary, contour for contour, after four billion years, and why fifty years of debate [4] has not settled it.
The other thing worth noticing is how thin the seismic base is. Almost everything known about Mars's deep interior comes from InSight, a single station in the northern lowlands operating from 2018 to 2022 [14], roughly four years of listening from the cold, stiff side [16]. One station cannot tell north from south, so most later interior models simply assumed the same rocks at the same temperature at any given depth, all the way around [15]. The gravity route gets around that with archive material: velocity wobbles of Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter [6], 16 years of radio tracking [5], which is about eight and a half Martian years of tidal cycles [17].
If the structure holds, it becomes answerable for more than topography. The team suggests a hot southern mantle could account for the magnetic anomalies in southern iron minerals, implying a field once strong enough to imprint a north-south difference [20]. Co-author Amirhossein Bagheri, a Caltech postdoc and former InSight team member, ties the dichotomy to Martian hydrology and the formation of basins that may have held water [21]. One structure carrying several observations is efficient, and also fragile: a better anelasticity measurement could take all of it down at once.
