NASA's InSight lander discovers possible evidence of Mars' liquid core

This was the first mission of its type, dedicated entirely to studying the innards of Mars. Knowing what lies underneath is critical to understanding the planet's formation and evolution. It could also help to understand the existence of any clues of life that the planet may have supported in its water-rich past. 

Data from RISE instruments 

RISE (Rotation and Interior Structure Experiment) was a dedicated radio-science transponder on InSight. 

This equipment relays radio signals from the lander to Earth. These signals might be used to track minor variations in the rotation of Mars and its wobbles (nutations). And both of these inputs can provide information about the planet's interior structure.

“The RISE transponder has the ability to establish communication with gigantic (up to 70 m dish) radio-telescopes on Earth and of measuring the tiniest variations of the distance between a lander on Mars and Earth, caused by the orbital and rotational movements of the two planets,” said Sébastien Le Maistre, who is the lead author of this new study, in an official release. 

Signature of a liquid core 

The scientists discovered a signal in the data that can only be explained by the presence of a liquid core.

The researchers discovered "internal mass anomalies deep within the mantle" of Mars by monitoring shifts in radio waves. 

These internal anomalies were discovered to extend from the top to the bottom of the mantel. 

“For the first time, we detected at such a large distance, hundreds of millions of km, the 40 cm oscillations due to the presence of the Martian liquid core. These oscillations are affected by a resonant behavior that only occurs when the core is liquid,” explained Le Maistre. 

In this study, the scientists added several other characteristics not previously included for estimating the liquid core. These variables included dust storms, changes in Mars' rotational speed, and nutations caused by the gravitational attraction of the Martian moons Phobos and Deimos. All these elements contributed to accurately determining the planet's rotation. 

This detailed assessment of the internal structure also verified the data obtained by the seismometer on InSight, which had previously suspected the liquid core. 

“Using the novel data we have determined the radius of the liquid core, confirming the value deduced from seismic data, and estimated the density difference between the mantle and the core. Moreover, we have been able to determine the shape of the core, which can only be explained if mass anomalies exist deep within the mantle. Taken together, those new findings increase our knowledge about the interior structure of Mars, its formation, and subsequent evolution,” mentioned Attilio Rivoldini, an expert on the interior of Mars. 

The team posits the Martian core is most likely formed of a liquid of iron and sulfur.  

The team intends to use the LaRa (Lander Radioscience), an instrument designed along the lines of RISE, to study further and demystify the mysteries of the Martian surface. However, that’s not happening anytime soon, as LaRa is waiting for the next Martian mission to fetch a ride.

The results have been published in the journal Nature.

Study abstract:

Knowledge of the interior structure and atmosphere of Mars is essential to understanding how the planet has formed and evolved. A major obstacle to investigations of planetary interiors, however, is that they are not directly accessible. Most of the geophysical data provide global information that cannot beseparated into contributions from the core, the mantle and the crust. The NASA InSight mission changed this situation by providing high-quality seismic and lander radio science data1,2. Here we use the InSight’s radio science data to determine fundamental properties of the core, mantle and atmosphere of Mars. By precisely measuring the rotation of the planet, we detected a resonance with a normal mode that allowed us to characterize the core and mantle separately. For an entirely solid mantle, we found that the liquid core has a radius of 1,835 ± 55 km and a mean density of 5,955–6,290 kg m−3, and that the increase in density at the core–mantle boundary is 1,690–2,110 kg m−3. Our analysis of InSight’s radio tracking 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 within the mantle. We also find evidence of a slow acceleration in the Martian rotation rate, which could be the resultof a long-term trend either inthe internal dynamics of Mars or in its atmosphere and ice caps.