Recent research has revealed that Mars possesses an interior structure strikingly similar to that of Earth. Findings from NASA's InSight mission suggest that the red planet features a solid inner core encased in a liquid outer core, potentially shedding light on a longstanding enigma surrounding its geological history. These groundbreaking results, published in the prestigious journal Nature, hold significant implications for our understanding of how Mars evolved over billions of years.
In the distant past, Mars may have boasted a much thicker atmosphere, which could have supported the presence of liquid water on its surface. This thicker atmosphere may have been maintained by a protective magnetic field, akin to the one that envelops Earth. However, Mars currently lacks such a magnetic field, leading scientists to question whether its absence facilitated the gradual loss of the atmosphere to space. This atmospheric depletion has contributed to Mars transforming into the cold, arid desert we observe today.
A key attribute of Earth is its core, which consists of a solid center surrounded by a liquid outer layer. The convection in this liquid layer generates a dynamo effect, producing a magnetic field that deflects charged particles emitted by the sun. This magnetic field plays a crucial role in preventing atmospheric erosion, allowing for the habitable conditions we enjoy on Earth. Evidence suggests that Mars once had a similar magnetic field, likely stemming from a core structure reminiscent of Earth's. However, it appears that at some point in its history, Mars' core cooled and ceased movement.
Despite the current thin atmosphere of Mars, there is substantial evidence that liquid water once flowed across its surface, indicating more hospitable conditions in the past. This evidence manifests in various forms, including dry lake beds containing minerals formed underwater, as well as extensive valley networks carved by rivers and streams. Yet, today, the necessary quantities of liquid water are nowhere to be found on the Martian surface.
The journey toward understanding Mars' core structure took a significant step forward with the deployment of NASA's InSight lander. Utilizing seismometers, the InSight team first identified the Martian core and found it to be primarily liquid. New research led by Huixing Bi from the University of Science and Technology of China, along with colleagues, indicates that there may also be a solid inner layer within this liquid core.
The question of Mars' interior structure has long puzzled scientists: Was it ever like Earth, with a dynamic liquid layer surrounding a solid core? Or did the red planet's smaller size hinder the formation of such structures? Understanding these aspects is crucial for piecing together Mars' evolutionary journey. The interplay of Mars' atmosphere, water presence, and core structure has sparked interest in numerous high-profile Mars missions.
While NASA’s Mars rovers—Spirit, Opportunity, Curiosity, and Perseverance—have explored surface mineralogy, other missions like the European Space Agency's ExoMars Trace Gas Orbiter are examining the Martian water cycle. Additionally, NASA's Maven spacecraft is investigating atmospheric loss, while the InSight lander focuses on seismic activity.
In 2021, Simon Stähler from ETH Zurich and colleagues published a pivotal paper analyzing seismic waves generated by Mars quakes. This analysis provided the first evidence of the Martian core and helped to determine its size and density. Their model suggested a single liquid core layer, which was unexpectedly larger and less dense than anticipated, with no solid inner core identified. Subsequent studies revealed a core around 900 km in radius, indicating it contained lighter elements like carbon, sulfur, and hydrogen.
The recent discovery of a solid inner core, reported by Huixing Bi and colleagues, is immensely significant. The mere existence of this solid layer indicates that crystallization and solidification are occurring as Mars cools. This core structure bears a closer resemblance to Earth's, making it more plausible that a dynamo effect was present in Mars’ past. On Earth, thermal changes between the solid inner core and liquid outer layer drive convection, which in turn generates a magnetic field.
With contrasting findings from Stähler and Bi, one might expect controversy; however, this scenario illustrates the progress being made in scientific data collection and analysis. InSight, which landed on Mars in November 2018, continued to transmit data until December 2022. Stähler's original model was later refined by Henri Samuel from Université Paris Cité, leading to a revised understanding of Mars' core size and density. This evolution of research showcases the scientific community's commitment to exploring the mysteries of the Martian interior.
Understanding the interior structure of planets within our solar system is vital for developing theories about their formation, growth, and evolution. Prior to the InSight mission, models of Mars that mirrored Earth's structure were considered, but they lacked substantial support. As new data emerges, the scientific community will continue to examine the implications of these findings and their relevance to our understanding of planetary climates and atmospheres.
