Mars Has Liquid Guts and Weird Insides, InSight – Ars Technica suggests

Image of a lander on a dry, reddish planet showing two circular solar panels and several instruments.
Increase / Artist’s impression of what InSight looked like after landing.

Mars appears to be a frozen expanse of red dust, craters and rocky terrain on the outside, but what lies beneath its windswept surface? NASA’s InSight lander may have discovered it before it took its proverbial last breath in the dust storm.

Whether the core of Mars is solid or liquid has long been debated. Although there is no way to directly observe the core of Mars, InSight tried. Its seismometer, SEIS, was the first instrument to find possible evidence of a liquid core. Meanwhile, its RISE (Rotation and Internal Structure Experiment) instrument measured tiny changes in the planet’s rotation as it orbited, “wobbled” on its axis, caused by the Sun’s gravitational push and pull.

“Our analysis of InSight radio tracer data argues against the existence of a solid inner core and reveals the shape of the core, indicating that there are internal mass anomalies deep in the mantle,” the instrument’s researchers wrote in a recently published study. Nature.

Slowly to RISE

RISE works by transmitting radio signals to Earth. By tracking changes in these signals, researchers can detect extremely small changes in its location relative to our receivers. These changes cause fluctuations in the rotation of Mars, called nutations. The distance and direction the axis moved due to these nutations can be used to infer information about the internal composition of Mars.

The Red Planet was previously thought to have a liquid core based on measurements of seismic waves. But detecting these changes based on radio signals proved difficult. It took some time for signals to emerge from the noise of the planet’s movements. Mars also churns up dust storms, and the storms that occurred before and after InSight landed changed the planet’s rotation rate for a while. Its axis of rotation also undergoes slight changes due to the gravitational forces exerted by the moons Phobos and Deimos.

For the RISE experiment to work, researchers needed to know exactly where InSight landed on Mars. The landers have planned landing sites, but they’re not precise—even the scientists following them can’t pinpoint where they are until they interpret the first data the lander sends back to Earth.

The first RISE data was processed by radio scientist Sébastien Le Maistre of the Royal Observatory of Belgium, and the positional estimate was uploaded to the Mars Reconnaissance Orbiter (MRO), which took an image of the site. The image showed that InSight was located with amazing accuracy.

There are nutations in your rotation

After RISE learned exactly where its lander was on Mars, how did the nutations it discovered indicate a liquid core? Nutations can be progressive (the axis moves counterclockwise relative to its surroundings) or retrograde (opposite). Le Maistre and his team already knew that if Mars really had a liquid core beneath a solid shell, that would mean the axis would oscillate backwards and also move a bit more than if the core were solid. When they checked it with InSight data, it was a coincidence.

“Nutational analysis based on radiometric measurements is the only method that can provide direct estimates [the] Properties of the Martian core,” the researchers also stated in the study.

Further analysis revealed that the Martian core is likely made of an alloy of liquid iron and sulfur, and that it is constantly undergoing convection, with hotter liquid rising and cooler liquid sinking. Unlike the Earth’s core, it is also believed to be completely liquid. Earth’s outer core is an alloy of liquid iron and nickel, while the inner core is solid and made mostly of iron.

Scientists say it is possible that Mars’ lower mantle may also have melted, which would affect the size and shape of the core. Molten mantle could create underwater mass anomalies, regions where material is more or less dense than the surrounding material. It turned out that one of these anomalies appeared to be much deeper below the surface than the other. The anomalies could partly explain the slight flattening of Mars’ surface and core as it spins on its axis.

In the future, Le Maistre hopes to analyze more RISE data in the same data set that removed the anomalies and the liquid core. There is still a huge amount of data available from InSight, just waiting to tell us more about Mars. “RISE is not just about deep inside, it’s about atmosphere and rotation,” he said in a press release. “[It can] provide an orientation and rotation model that can serve as a reference for the scientific community.

Nature, 2023. DOI: 10.1038/s41586-023-06150-0

Elizabeth Rein is a writing creature. Her work has appeared on SYFY WIRE,, Live Science, Grunge, Den of Geek, and Forbidden Futures. When not writing, she’s either shape-shifting, drawing, or cosplaying as a character no one has ever heard of. Follow her on Twitter @quothravenrayne.

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