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Saturn has not always had rings



Analyzes of data from Cassini's last days suggest that the rings are a late addition and use them to solve a Saturnian mystery.

  Cassini Grand Finale

An artist's view of Cassini throwing through the gap between Saturn and its rings. NASA / JPL

If the early dinosaurs had star celebrations, they probably weren't impressed with Saturn. Based on data from Cassini's spacecraft's last hurray, planetary scientists are planning that the iconic hula hoop of icy particles enclosing Saturn is a relatively new addition.

Astronomers have made this suggestion before, but with different hesitation. What they really needed was a good understanding of how many things the rings contain, and how quickly they get dark by catching space waste. These types of information will indicate how long the rings could survive in their current ice-cold state.

Cassini gave a unique opportunity to test the hypothesis. When the spacecraft's gas meter sank to the ground, the missionaries switched the orbiter to take 22 daredevil dives between the planet and its rings. As it went through, the spacecraft felt gravity on both the planet and the rings. Luciano Iess (Sapienza University of Rome) and colleagues made a complex analysis of these dives and plagued the ring's contributions from the planet.

Report January 1

7 in the journal Science the team concludes that rings have a mass of 15 million trillion (1.5 x 10 19 kg), about 40% of Saturn's mid-size month Mimas or about a millionth of the earth's mass. Other Cassini data also show that approx. 10 times more room dust is counting on the rings than expected, which means they cannot be too old and look as bright as they do. Combined with other measurements, the observations support an age for the rings of approx. 10 million to 100 million years, favoring the higher end of this range. Earlier work suggests that the rings do not last forever, either – maybe another few hundred million years.

Top end of age group echoes, previously suggested for several of Saturn's middle ice moon. Some planetary scientists believe that these satellites are formed from a previous generation of lunar masts who smashed into one another and wiped out. However, how this event and the current ring system can be connected remains unclear: It is difficult to understand why detritus constituting the rings would have migrated so close to the planet rather than lump into further moons further out, the team notes. paper. An alternative idea is that Saturn captured a transient comet or icy asteroid and tore it apart and then attached it to the wreck.

In a separate study, graduate students Christopher Mankovich (University of California, Santa Cruz) used the rings to answer a decade-long question: How long is Saturn's day?

Astronomers can determine the duration of Jupiter's day based on a periodic radio signal, created as Jupiter twirls around the planet's mismatched rotational and magnetic axes. But Saturn's magnetic field is almost perfectly matched to its axis of rotation.

Instead, Mankovich and his colleagues used Saturn's rings as a kind of seismometer. Vibration in the planet causes shifts in its gravitational field and these create wave patterns in the rings. The patterns of the patterns again show how fast the planet rotates: 10 hours, 33 minutes and 38 seconds. This estimate is nearly 6 minutes shorter (and far more solid) than one based on Voyager data. The results are shown on January 20 Astrophysical Journal .

Read more about the age of the rings in press releases from NASA JPL and the University of California, Berkeley. You can find more about day measurement in publications from the University of California, Santa Cruz and NASA JPL.

References:

Luciano Iess et al. "Measurement and Impact of Saturn's Gravity Field and Ring Mass." Science . January 17, 2019.

Christopher Mankovich et al. "Cassini Call Seismology as a Probe of Saturn's Interior. I. Stiff Rotation." Astrophysical Journal . January 20, 2019. Full preprint text here.

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