SCIENTISTS have revealed that Mars’ innermost core appears to be a solid metallic sphere, much like Earth’s, according to a Chinese?led study published last week. The team based its conclusions on seismic readings recorded by NASA’s InSight lander, which measured more than 1,300 marsquakes before ceasing operations in 2022. InSight touched down on a broad plain near Mars’ equator in 2018 and provided the first extended seismic record from the red planet. Earlier studies had pointed to a largely liquid core. The new analysis, however, indicates that Mars has a small but solid inner core surrounded by a molten metal outer core. The inner core extends from the planet’s center to a radius of roughly 613 kilometers, the researchers report in Nature. The liquid outer core spans from that boundary out to as far as about 1,800 kilometers from the center. Sun Daoyuan, one of the study’s lead authors from the University of Science and Technology of China, said crystallization of the inner core may have begun in the past and could still be progressing today. He noted that Mars’ core would originally have been entirely liquid. It remains unclear whether the outer core contains suspended solid material — such as droplets — or whether a “mushy zone” exists near the inner-outer core boundary. Although InSight recorded more than 1,300 marsquakes overall, this study relied primarily on 23 relatively weak events whose epicenters lay between about 1,200 and 2,360 kilometers from the lander. Analysis of seismic wave behavior across those events led the team to infer a roughly 30% increase in wave velocity and a 7% density contrast between the outer and inner cores. From these constraints the researchers modeled likely mineral compositions for the inner core. Their results suggest a core composed mainly of iron and nickel, with significant light?element content: about 12–16% sulfur, 6.7–9% oxygen, and up to 3.8% carbon. “Our results suggest that Mars has a solid inner core making up about one?fifth of the planet’s radius — roughly the same proportion as Earth’s inner core,” Sun said. “However, this similarity may be coincidental.” Not all experts consider the issue settled. Nicholas Schmerr of the University of Maryland, who was not involved in the study, praised the work but warned that many details remain unresolved. With InSight no longer collecting data, no new marsquake recordings are available to refine models of Mars’ deep interior, he pointed out. “There are a lot of details about the exact shape of the inner core and the composition of the inner and outer core of Mars that will require a network of InSight?like seismometer stations to resolve,” Schmerr said. Further modeling and additional seismic data will be needed to clarify how the inner core formed and what it implies about Mars’ magnetic history, Sun added. At present, Mars lacks a global magnetic field — a condition that may be linked to slow or limited core crystallization.(SD-Agencies) | 