NASA scientists say they have solved a mystery that has lasted a long time: a day on the planet Saturn.
The researchers said it was 10 hours, 33 minutes and 38 seconds.
Planet scientists have been trying to find out for decades, but they have not been able to because Saturn is made of gas.
It also doesn't have a solid surface with landmarks that can be tracked when spinning.
It also has an unusual magnetic field that blurs the rotation rate.
But the researchers said they found it using new data from NASA's Cassini spacecraft.
They can study the wave pattern in Saturn's ring to find out the length of the day.