Mars is spinning faster and its days are getting shorter — and scientists aren't sure why

• Measurements from NASAs' InSight Mars Lander have uncovered a new Martian mystery.
• The red planet seems to be spinning faster, making its days a little shorter every year.

Our days on Earth may be getting longer, but on Mars, they are mysteriously getting shorter.

The red planet's rotation is speeding up by 4 milliarcseconds per year, which in turn makes the Martian 24.6-hour-day a few fractions of a millisecond shorter every year, according to NASA.

The discovery, made using measurements from NASA's Insight lander, has left scientists baffled.

"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," said aerospace engineer Sebastien Le Maistre of the Royal Observatory of Belgium, a lead scientist on the study.

While researchers aren't exactly sure what could be causing this landmass shift, a leading theory suggests it could be down to Martian ice.

Though the red planet may look like a barren wasteland from afar, there is ice on Mars, usually a mixture of water and carbon dioxide ice (or dry ice).

Martian ice has been detected in several places around the planet, but it is most visible at the poles, growing and thawing with the seasons.

This could be also triggering a process called post-glacial rebound, said NASA. This is when land that was trapped under a large mass of ice bounces up after that ice melts.

A little melting ice doesn't seem like it should be heavy enough to affect the rotation of such a huge planet. But this isn't unheard of.

For instance, the Earth's rotation around a polar axis is thought to have drifted about 13 feet since the 80s because of its melting glaciers.

Meanwhile, the moon's gravitational pull has been making our days ever so slightly longer. Scientists estimate that the pull adds around 2.3 milliseconds to the length of each day every century.

The latest findings about Mars are the result of years of data gathered from NASA's Insight Lander over 900 Martian days.

The lander gathered information about quakes and meteor impacts on the red planet for four years before it ran out of power after its solar panels became covered in dust. But scientists are still learning from the data that was sent back over that time.

"It's really cool to be able to get this latest measurement — and so precisely," said InSight's principal investigator, Bruce Banerdt of NASA's Jet Propulsion Laboratory in Southern California in the press release.

"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."