Saturn's rings haven't always been there

Rainfall detected on Saturn's moon Titan

Iess said NASA's Voyager spacecraft-as well as Cassini-had already provided clues that the rings had not formed with Saturn.

When orbiting Titan, the Cassini spacecraft captured something reflective on the moon's north pole that covered about 46,332 square miles - a "bright ephemeral" reflective feature that didn't appear on previous or subsequent images taken as Cassini repeatedly passed.

After analyzing the final set of orbits in September 2017, however, the extent to which Cassini's trajectory was deflected initially didn't make sense. In effect, the rings act as an extremely sensitive seismograph by responding to vibrations within the planet itself.

According to Mankovich's research published Thursday by Astrophysical Journal, he developed models of Saturn's internal structure that would match the rings' waves. Saturn itself formed about 4.5 billion years ago in the early years of the solar system. Saturn only acquired its rings relatively recently, and for most of its existence it has been as bare as Earth.

Researchers have used new data from NASA's Cassini spacecraft to find out the length of a day on Saturn, which is 10 hours, 33 minutes and 38 seconds.

Luckily, as Cassini approached the end of its life, NASA programmed it to perform 22 dives between the planet and the rings to probe Saturn's gravity field.

Scientists usually rely on magnetic fields to measure planets' rotation rates.

The scientists assessed Saturn's gravitational field by measuring a microwave signal that Cassini sent to receivers on Earth during its "Grand Finale orbits".

Whatever happened, it's looking more and more likely that Saturn's splendid rings are a temporary phenomenon that humans are lucky to get to see at all.

Gravity readings Cassini took from Saturn (rather than its rings) suggest the planet has a mass around 15-18 times that of Earth.

"We predict that there is a massive jet near the equator that rotates 4% faster than the rest of the planet", says team member Burkhard Militzer, of the University of California, Berkeley. Saturn, which is mostly made up of hydrogen and helium, has an interesting atmosphere.

The length of a day on each of our solar system's planets ranges from a mere 10 hours on Jupiter, all the way up to 5,832 hours on Venus.

The prevalence of dust storms and strong winds on Titan implies that the underlying sand can be moved as well and that the "giant dunes" that cover the moon's equatorial regions are constantly changing and still active.

"They used the rings to peer into Saturn's interior, and out popped this long-sought, fundamental quality of the planet". The rings, in turn, detect those movements in the field.

Saturn's E ring, meanwhile, has its own unique source: plumes of water vapor streaming into space from the moon Enceladus, believed to harbor an ocean beneath its surface. Sensors on the spacecraft measured, essentially, how much the gravity of the planet and of the rings tugged it back and forth.

He continued: "Although we don't yet know why, something catastrophic happened, perhaps in the age of the dinosaurs, that resulted in Saturn having a ring system completely unlike Jupiter and the ice giants Uranus and Neptune". Now, Dhingra said the researchers have to "figure out what caused delay".

Iess and colleagues describe their observations in Science.



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