Astronomers determined that the planet’s spin is increasing by about 4 milliarcseconds per year², or shortening the length of a Martian day by a fraction of a millisecond per year. A Martian day lasts about 40 minutes longer than a day on Earth.

The increased acceleration seems incredibly small, and researchers aren’t quite sure what is causing it. However, they suggest it might be due to ice accumulation at the Martian poles or the rise of landmasses after being covered in ice. When a planet’s mass shifts in this way, it can cause the planet’s spin to accelerate.