New research using NASA’s InSight seismic waves reveals Mars has a solid inner core

Mars may share structural similarities with Earth, according to new research using seismic data from NASA’s InSight lander. Between 2018 and 2022, InSight recorded over 1,300 Marsquakes, allowing scientists to probe deep beneath the planet’s surface. The findings, published in Nature, suggest Mars has a solid inner core about 600 kilometres in radius, surrounded by a liquid outer core. This hardened heart, composed mainly of iron and nickel with lighter elements, challenges previous ideas of a fully liquid core. The discovery could reshape theories about Mars’ past, particularly how and why it once generated, and then lost, its global magnetic field.From late 2018 to 2022, NASA’s InSight lander sat on Mars’ dusty surface, recording the planet’s subtle rumblings. During its mission, it detected more than 1,300 Marsquakes, offering scientists the most detailed insight yet into the Red Planet’s hidden layers. Just as earthquakes help researchers understand Earth’s deep structure, Marsquakes acted as natural probes. Their seismic waves bent, bounced, or reflected as they travelled through different layers, leaving behind vital clues about what lies beneath Mars’ surface.The analysis, published in Nature in September 2025, revealed something unexpected: evidence that Mars has a solid inner core about 600 kilometres in radius, surrounded by a liquid outer core. This hardened heart, likely made mostly of iron and nickel mixed with lighter elements, challenges earlier models that suggested Mars’ core was entirely liquid. The discovery could transform our understanding of the planet’s history, including how it once generated a global magnetic field and why that shield eventually disappeared, leaving Mars the cold, barren world we see today.For years, scientists knew Mars had a liquid metal core, but whether it also had a solid inner heart remained uncertain. On Earth, the solid inner core is a key feature that helps sustain the magnetic field protecting our planet.Seismologist Daoyuan Sun of the University of Science and Technology of China and colleagues analysed 23 low-frequency Marsquakes, located about 1,600 to 2,400 kilometres from InSight.The team noticed that some seismic waves travelled through Mars’ core and arrived 50 to 200 seconds earlier than expected if the core were entirely liquid. This suggested a denser, solid layer deep inside. Other waves even appeared to ricochet off a boundary between the inner and outer core, evidence that points strongly to the existence of a hardened heart.By calculating wave travel speeds and paths, researchers estimated the solid inner core’s radius to be around 600 kilometres. That makes it roughly one-fifth of the planet’s thickness.The team’s computer simulations indicate that Mars’ inner core is mostly iron and nickel, potentially mixed with oxygen. The surrounding liquid outer core likely contains a blend of sulphur, oxygen, and carbon, which explains its lower density.If Mars truly has a solid inner core, it could rewrite theories about the planet’s past. Early in its history, Mars had a global magnetic field, similar to Earth’s. This shield once protected its atmosphere from being stripped away by solar winds.On Earth, the magnetic field is powered partly by the growth of the solid inner core and heat flowing from the outer core. Mars, however, lost its global magnetic field billions of years ago. If the Red Planet does have a hardened heart, scientists will need new explanations for why its magnetic shield disappeared.Uncovering a solid core inside Mars is more than a scientific curiosity, it may help answer bigger questions about planetary formation and evolution. Understanding how Mars’ interior differs from Earth’s provides clues about why the Red Planet became a barren desert world while our own remains habitable.NASA’s InSight mission may have ended in 2022, but the data it collected continues to deliver groundbreaking discoveries. With new analysis techniques, researchers hope to confirm whether Mars truly has a solid core and what role it played in shaping the planet’s history.