Mars Wobble & Core Size Confirmed By NASA's InSight Lander

Scientists have unveiled the most accurate measurements ever recorded of Mars' rotation, shedding light on the planet's subtle wobble caused by the movement of its molten metal core. The remarkable findings draw upon data gathered by NASA's InSight Mars lander, which diligently operated for an impressive four years before concluding its extended mission in December 2022.

Using InSight's Rotation and Interior Structure Experiment (RISE), a sophisticated array consisting of radio transponders and antennas affixed to lander, researchers were able to meticulously monitor the spin rate of Mars, leading to the unearthing of a surprising revelation.

Mars' rotation is undergoing an acceleration of approximately 4 milliarcseconds per year, resulting in a minuscule but perceptible shortening of the Martian day by a fraction of a millisecond annually.

The cause of this subtle acceleration remains an intriguing enigma, with scientists speculating on several potential factors. Among these ideas is the possibility of ice accumulation on the planet's polar caps or the phenomenon of post-glacial rebound, wherein landmasses elevate after being released from the weight of ice. Analogous to an ice skater executing a spin and subsequently retracting their outstretched arms, this shift in mass can induce acceleration in a planet's rotation.

How Does RISE Work?

Rotation and Interior Structure Experiment (RISE) is part of a Mars exploration tradition using radio waves for science, builds upon previous missions like Viking and Pathfinder.InSight's advanced radio tech and upgraded Deep Space Network antennas offer data five times more accurate than Viking.

RISE involves beaming a radio signal to InSight, which reflects it back for analysis. Doppler shift in the reflected signal helps determine Mars' rotation speed.

“What we’re looking for are variations that are just a few tens of centimeters over the course of a Martian year...It takes a very long time and a lot of data to accumulate before we can even see these variations.” - Sebastien Le Maistre, Lead Author and RISE’s Principal Investigator at the Royal Observatory of Belgium.

A recent study used InSight data from 900 Martian days.

“We have spent a lot of time and energy preparing for the experiment and anticipating these discoveries. But despite this, we were still surprised along the way – and it’s not over, since RISE still has a lot to reveal about Mars.” - Sebastien Le Maistre, Lead Author and RISE’s Principal Investigator at the Royal Observatory of Belgium.

Mesuring The Mars Core

Scientists have also be able to use RISE data to gauge Mars' nutation, an oscillating movement caused by the sloshing of its liquid core. 

This measurement enabled scientists to estimate the core's dimensions at approximately 1,140 miles (1,835 kilometers). Researchers then compared this value with two previous measurements of the core obtained InSights seismometer. They specifically analyzed the behavior of seismic waves as they traversed the planet's interior, assessing whether they encountered resistance from the core or propagated through it unhindered.

By considering all three measurements, they estimated the core's radius to fall within the range of 1,112 to 1,150 miles (1,790 to 1,850 kilometers), approximately half the size of Earth.

The assessment of Mars' wobble also yielded insights into the core's shape.

“It’s really cool to be able to get this latest measurement – and so precisely...I’ve been involved in efforts to get a geophysical station like InSight onto Mars for a long time, and results like this make all those decades of work worth it.” - Bruce Banerdt, InSight Principal Investigator at NASA’s Jet Propulsion Laboratory

The implications of this revelation are far-reaching, as they provide a deeper understanding of Mars' internal dynamics and its geological evolution over time.

This achievement underscores the tremendous advancements in planetary exploration and scientific ingenuity that continue to reshape our understanding of the universe.