Mars is spinning faster. We don't know why

Scientists have revealed that Mars is spinning faster than previously thought.

The data, collected by NASA's InSight Mars lander before it retired in December 2022, has provided new insights into the planet's rotation and wobble.

The study, published in Nature, relied on one of InSight's instruments, the Rotation and Interior Structure Experiment (RISE).

RISE used advanced radio technology and upgrades to antennas within NASA’s Deep Space Network on Earth to track the planet's spin rate.

The findings showed that Mars' rotation is accelerating by about 4 milliarcseconds per year, resulting in a slight shortening of the Martian day.

Bruce Banerdt, InSight’s principal investigator from NASA’s Jet Propulsion Laboratory in Southern California, expressed his excitement over the precision of the latest measurement. He said, "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.”

The acceleration in Mars' rotation is subtle, and scientists are still unsure of the exact cause.

However, they speculate that it could be due to ice accumulating on the polar caps or post-glacial rebound, where landmasses rise after being buried by ice. This shift in a planet’s mass can cause it to accelerate, similar to an ice skater spinning with their arms stretched out and then pulling them in.

The study also used RISE data to measure Mars’ wobble, known as its nutation, caused by the sloshing of its liquid core.

This measurement allowed scientists to estimate the size of the core, which they believe has a radius of roughly 1,140 miles.

Attilio Rivoldini of the Royal Observatory of Belgium, the paper’s second author, stated that the shape of Mars' core cannot be explained by its rotation alone. He suggested that the shape requires regions of slightly higher or lower density buried deep within the mantle.

This study marks a significant milestone in our understanding of Mars and the final chapter for Banerdt’s role as the mission’s principal investigator.

After 46 years with JPL, he retired on August 1. However, scientists will continue to analyze InSight's data for years to come, potentially unveiling more secrets about the Red Planet.