Length of a day on Mars is shrinking as planet is strangely spinning faster every year, Nasa says

Data from Nasa’s InSight Mars lander suggests the Red Planet’s rotation is strangely accelerating every year, leading to a fractional shortening of the length of the Martian day.

The research, published recently in the journal Nature, found Mars’ rotation on its axis is accelerating by about 4 milliarcseconds each year – corresponding to a shortening of the Martian day by a fraction of a millisecond per year.

Scientists, including those from Nasa’s Jet Propulsion Laboratory in California, are unsure what is causing this subtle speeding up of the Red Planet’s rotation, but they have some ideas.

“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,” study co-author Bruce Banerdt said.

In the research, scientists made the most precise measurements ever of Mars’s rotation as well as detecting how the planet wobbles due to the “sloshing” of its molten metal core.

The study suspects factors such as ice accumulating on Mars’ polar caps or post-glacial rebound where landmasses rise after being buried by ice could be behind this acceleration of the planet’s spin.

Nasa likens this shift to the change in rotation speed to an ice skater spinning with their arms stretched out and pulling their arms in.

The new research assessed data from InSight’s first 900 Martian days to look for variations in the planet’s rotation.

For the study, scientists used Nasa’s Deep Space Network on Earth, and InSight’s instruments – a radio transponder and antennas collectively called RISE.

They would beam a radio signal to the lander using the Deep Space Network which RISE would then reflect back to Earth.

In the reflected signal, researchers would look for tiny changes in frequency caused by the Doppler shift – the same effect that causes an ambulance siren to change pitch as it gets closer and farther away.

By measuring this shift, they could determine how fast the planet rotates.

“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,” said study lead author Sebastien Le Maistre from the Royal Observatory of Belgium.

“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,” said Dr Le Maistre.

The new findings suggest there is a “slow acceleration” in the Martian rotation rate.

Scientists conclude that this could be an indication of a “long-term trend” either in the internal dynamics of Mars or in its atmosphere and ice caps.