Comments on: The rings of Saturn

By: BSJ

BSJ — Wed, 22 Mar 2017 11:54:24 +0000

My response was to The Local Fluffer’s “If ringed planets were common,” comment.

100% in our system makes ’em pretty common in my book.

By: LocalFluff

LocalFluff — Tue, 21 Mar 2017 23:40:51 +0000

Even Mars will have rings in only 10-30 million or so years (at 99% of Mars’ existence, active old warrior!) when its moon Phobos disintegrates from tidal forces. It is supposed to transform from a discernible moon to a ring within a matter of weeks when it happens. Phobos is a more than half-vacuous “ring in a box” to be delivered. Rings could be common also at terrestrial planets.

Earth cannot have any small rubble pile moonlet because our Big Sister Luna wouldn’t accept it with her eccentric orbit. Luna has cleared away anything during her billions of years long spiraling outwards.

Venus could’ve had moonlets like Phobos. Maybe that was what destroyed her life? After having been endowed with a ring of marriage for a while before it came crashing down and melted her surface maybe about 0.3 billion years ago.

Mercury is way too eccentric, the Sun would’ve rubbed him of any moonlets right from the nursery home.

The (new) planet definition is based on roundness. If a collection of mass is great enough to have its own gravity push it to became round(ish), then it will also stick together. Anything less than roundish is at great risk of being tidally disrupted by anything major in its vicinity. The Moon will never get tidally disrupted (because it is round). Phobos will (because it isn’t round). That is probably not an explicit part of the new planet definition (because there are likely some exceptions), but it is an argument for it.

By: Robert Zimmerman

Robert Zimmerman — Tue, 21 Mar 2017 21:45:28 +0000

In reply to BSJ. BSJ: Of course they all do. But when you can take a picture of Jupiter, Neptune, Uranus and show a ring as striking as Saturn's, talk to me then. The differences here are quite profound. Don't be silly and make believe they don't exist.

By: BSJ

BSJ — Tue, 21 Mar 2017 19:26:00 +0000

All of our gas giants have rings.

By: LocalFluff

LocalFluff — Tue, 21 Mar 2017 19:06:45 +0000

If ringed planets were common, I would think that many confirmed transiting exoplanets would have had them. I don’t think more than a handful out of 4000 exoplanets have been detected to have rings. There was an online talk on how to discover exoplanetary rings on the SETI institute just the other week, I haven’t seen, but Cassini makes this topic hot this year:
http://www.seti.org/weekly-lecture/search-extrasolar-moons-and-rings-using-transit-observations

Since the particles are so small and bafflingly well organized, just intuitively to me it looks as if the ring system is VERY long lived. What force is there around to disrupt this? Still I heard only months ago that they could be as young as 0.2 billion years, based on how three or so of the moons near the rings should’ve changed orbital resonances with each other. That was probably also a SETI talk.

By: Diane Wilson

Diane Wilson — Tue, 21 Mar 2017 18:00:24 +0000

If camera “speed” (really sensor speed) is the only issue, the result might be streaks in place of particles. We can still learn a lot from streaks. If the issue is resolution, well, we still don’t know the particle size, so I don’t think we can do more than guess. Yet.

I’d love to know how much real control the Cassini team has over its orbit. If Cassini could come close to matching velocity with the rings, then we would get some truly astonishing images.

This does promise to be an interesting year, with Cassini’s mission end, Juno, Curiosity finally across the dunes, and SpaceX’s several possibilities (Falcon Heavy, reusing both Falcon and Dragon, Dragon 2 first flight). Let’s hope that all the surprises this year are good ones.

By: BSJ

BSJ — Tue, 21 Mar 2017 17:25:15 +0000

I wonder if Cassini’s cameras are ‘fast’ enough to capture fine detail as it zip past on the closer approaches.