Monday, January 21, 2019

The Late, Great Cassini's Feast of Saturnalia -- The Ring-a-Ding-Ding Edition

I have to note this amazing finding from the intrepid and awesome Cassini probe -- a probe that will live on in memory forever for all the wonders of Saturn it uncovered -- that was just published in Science

It concerns the mass and hence age of Saturn's awesome ring system.

Here is the key part of an excerpt from an article in The Atlantic last week:

In its last maneuvers, Cassini wove in and out of Saturn's rings. The spacecraft was jostled by the gravity of the bands, as well as powerful winds emanating from deep within the planet’s atmosphere.

Scientists used the data produced by these effects to calculate the mass of the rings. They say that the mass is about 40 percent that of Mimas, a moon of Saturn, which is about 2,000 times as small as Earth’s moon.

In more earthly terms, the rings are about half the mass of the entire Antarctic ice shelf, spread across a surface area 80 times that of Earth.

"It is the most accurate measurement of the rings of Saturn," says Bonnie Buratti, a planetary scientist at NASA's Jet Propulsion Laboratory who worked on the Cassini mission but who was not involved in the study.

"The error margins are kind of pretty big -- there's about a 25 percent, almost 30 percent uncertainty -- but it's way more accurate than anything we've had before."

So! The mass of the mostly water ice that comprises Saturn's ring system -- ranging in size from sand grains to mountains -- is about half the mass of Antarctica's ice cap. And, remember, the rings of Saturn are only on the order of 10 meters to (at most 1 kilometer) thick.

More importantly, though, such a lightweight ring system (relatively speaking) implies that the rings (or at least most of them) are only 10 to 100 million years old and were possibly created by a wayward moon, comet, or asteroid that was ripped apart by Saturn's massive gravitational pull.

A couple of artist conception images of being inside the rings of Saturn …

Abstract of that Science article:

The interior structure of Saturn, the depth of its winds and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and the innermost ring, at altitudes 2600-3900 km above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings.

We find that Saturn's gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 km. The total mass of the rings is (1.54 ± 0.49)×1019 kg (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 107 to 108 years ago.

Artist's conception of the Saturnian atmosphere (above the clouds) with the rings prominently visible …




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