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The concept of "day" seems so obvious to humans that it is often a surprise that the day on other planets may be very different from ours. Perhaps even more shocking is that we did not know the duration of a day on Saturn until today. Thanks to the data collected by the Cassini mission, we finally have an answer to this long-standing mystery.


Saturn rotates on its axis in 10 hours, 33 minutes and 38 seconds.

Planetary scientists often use magnetic fields to estimate planetary rotation. If the magnetic field and rotational axis of a planet are not aligned, it is possible to measure periodic signals in radio waves that are repeated every day. But on Saturn, the magnetic field is almost in perfect alignment, so that was not possible.

Therefore, the researchers had to present a different approach and hypothesized that studying the rings of Saturn could be the key to finally defining a number. As the planet rotates, subtle differences in gravity generate waves within the rings, and they can be used to estimate the duration of a day.

"The particles along the rings cannot but feel these oscillations in the gravitational field of the planet," said Christopher Mankovich, a researcher at the University of California. "At specific locations in the rings, these oscillations pick up the particles at the right moment in their orbits to gradually accumulate energy, and that energy is carried as an observable wave," he concluded.

This result was made possible by Cassini's observations of the planet's rings. The mission team made the decision to crash the spacecraft on Saturn when it began running out of fuel, but not before being moved to a nearer and bolder orbit. This "Grand Finale" phase led Cassini between Saturn and its rings, giving researchers’ unparalleled visions. The mission, a collaboration between NASA, the European Space Agency and the Italian Space Agency, ended in September 2017. [ IFLS ]
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