Skip to main content

How long is a day on Saturn? Scientists finally have an answer

A puzzle about our Solar System — how long is a day on Saturn? — has kept astronomers up at night for years. This figure was hard to calculate: The gas giant has no solid surface so there are no landmarks to track as the planet rotates. And a magnetic field makes the rate of rotation hard to see. What to do?

Now NASA scientists have used data from the Cassini spacecraft to pin down an answer and solve the puzzle: A day on Saturn is ten hours, 33 minutes, and 38 seconds long. The new day length of 10:33:38 is somewhat shorter than previous estimates, such as the 10:39:22 estimation from 1981 based on magnetic field data from Voyager.

An image of Saturn captured by NASA’s Cassini spacecraft in 2016. The rings of Saturn have been used to work out the length of a day on the planet. NASA/JPL-Caltech/Space Science Institute

The new figure was calculated by looking at Saturn’s rings, about which Cassini gathered lots of detailed data during its mission from launch in 1997 to its eventual destruction in the planet’s atmosphere in 2017. During its orbit of Saturn from 2004 onward, the craft collected high resolution images of the planet and data on its icy, rocky rings. This data was then used by graduate student Christopher Mankovich to study wave patterns within the rings.

Mankovich found that the rings acted as a kind of seismometer, responding to vibrations that occurred within the planet. When the inside of the planet vibrates and earthquakes occur, the vibration frequencies cause variations in the planet’s gravitational field, and these variations are transmitted to the rings. “Particles throughout the rings can’t help but feel these oscillations in the gravity field,” Mankovich explained in a statement. “At specific locations in the rings these oscillations catch ring particles at just the right time in their orbits to gradually build up energy, and that energy gets carried away as an observable wave.”

This means that scientists can now track the movements of the planet’s interior, and from that tracking they can see the planet’s rotation. This is what allowed them to calculate the exact length of a day on Saturn. “The researchers used waves in the rings to peer into Saturn’s interior, and out popped this long-sought, fundamental characteristic of the planet. And it’s a really solid result,” said Cassini Project Scientist Linda Spilker in the same statement. “The rings held the answer.”

The paper is available at physics archive arXiv.

Editors' Recommendations

Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
Long-lost moon could explain how Saturn got its rings
Artistic rendering of the moon Chrysalis disintegrating in Saturn’s intense gravity field. The chunks of icy rock eventually collided and shattered into smaller pieces that became distributed in the thin ring we see today.

Saturn is famed for its beautiful rings, but these rings are something of a puzzle to astronomers. Originally, it was thought that they must have formed around the same time as the planet, over 4 billion years ago. But data from the Cassini spacecraft suggested the rings might be much younger than that, forming less than 100 million years ago. Now, a new study suggests that the rings could have been formed from a long-lost moon, explaining several of Saturn's peculiarities.

Saturn rotates with a tilt of 27 degrees, slightly off the plane at which it orbits the sun, and its rings are tilted too. Recently published research proposes that both of these factors can be explained by a former moon, named Chrysalis, which came close to the planet and was torn apart. Most of the moon was absorbed by the planet, but the rest of it created the stunning rings.

Read more
Hubble gets a peek at how stars could have formed in the early universe
Astronomers have been bemused to find young stars spiralling into the centre of a massive cluster of stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way. The outer arm of the spiral in this huge, oddly shaped stellar nursery — called NGC 346 — may be feeding star formation in a river-like motion of gas and stars. This is an efficient way to fuel star birth, researchers say.

With the early science results coming in from the James Webb Space Telescope we're learning more than ever before about the early universe. But it's not only Webb which is helping scientists to understand the universe when it was young -- as a recent release from the Hubble Space Telescope demonstrates, we also have a lot to learn from other tools too.

Hubble researchers recently shared this image of a cluster of stars in the Small Magellanic Cloud, a dwarf satellite galaxy of our Milky Way. This small galaxy has a different chemical composition than our galaxy and is therefore more like the galaxies found in the early universe, so studying it can help us learn about how stars were born when the universe was still young.

Read more
No one is quite sure how long a day on Earth lasts, it turns out
Earth as seen by NOAA's GOES-18 weather satellite.

As confusing and changeable as the world can be, there are some comforting certainties: The sun rises in the east, summer follows spring, and a day lasts for 24 hours. Right? Unfortunately, not even these basic tenets of life on Earth are set in concrete. In recent years, researchers have noticed that days on Earth are getting shorter, and no one knows exactly why.

The kind of shortening we're talking about is only noticeable due to atomic clocks, which can measure time with extreme accuracy. Since scientists began using these atomic clocks to measure the lengths of days, the record for the shortest day ever recorded was set in July this year.

Read more