Ponder Ring Origin

Image source with more information
Credit: NASA/JPL/Space Science Institute

This natural colour image of Tethys and Saturn's rings makes me dizzy. We're looking towards the unilluminated side of the rings - or to put it another way, the sun is shining on the other side of the rings from the side we see here. The thick black strip within the rings is not a gap, but the opaque B ring, which isn't letting any light through.

It's also worth checking out this short article. The Cassini imaging team have pieced together a likely history for Saturn's smaller moons (Pan, Atlas, Prometheus, Janus and others), a history which also provides further hints for the origin of the dazzling rings themselves. In short, Saturn's smaller moons seem to have formed from dense cores which have accumulated ring material into a somewhat larger light-and-frothy moon. The interesting question now is where those original dense cores came from. One obvious possibility is that they were the fragmentary remnants of larger moons that were shattered by impacts - part of one of the favourite hypotheses for the formation of Saturn's rings.


Udge said...

Surely the planetary-collision hypothesis raises more questions than it presumes to answer; for one: why does no other planet have rings, when most planets have moons?

But a lovely photo, as the Cassini's have all been.

Tinker said...

Lovely photo and hypothesis, but does the cheese in the larger, yet light and frothy moons have as many calories? o_0

Pacian said...

@U: Actually all four gas giants have a ring system of some kind. See here.

@T: Well I suppose there'd be less per unit of volume, but the same amount per unit of mass.

Udge said...

So rings relate more closely to gas-giant-ness than to having moons?

Pacian said...

That may be the case, unfortunately, gas-giant-ness is itself closely related to having lots of moons. The gas giants in our solar system each have moons amounting to about 1/10,000 of the planet's mass.

Meanwhile Earth is the only rocky planet to have a sizeable natural satellite - and according to one of the leading hypotheses for the Moon's formation, it may have condensed from a primordial ring around our own world ejected by a cataclysmic impact.

Udge said...

Fascinating. Knowledge itself is fractal: every step one towards a little knowledge of a topic, there appears a new body of detailed or related sub-knowledge equal to of greater than that which was just acquired.

Pacian said...

Yep, but it works the other way too. Learning about one subject means you end up finding out a bunch of adjacent stuff as well, with less effort than it'd take to learn it all separately.