Saturn's rings are far younger than once thought | Hacker News Reader

Saturn's rings are far younger than once thought

colorado.edu

79 pointsgeox35 comments

> The planet’s rings, in other words, are new phenomena, arising (and potentially even disappearing) in what amounts to a blink of an eye in cosmic terms.

If the universe is ~14 billion years, 400 million is only 1/35th. A person blinks thousands of times a day and maybe 400 million times in their lifetime. I don't really know but is 400 million years really a blink of an eye in cosmic terms?

A human blink takes about 0.1s. And spends roughly 75 years alive.

Blink/s/min/hr/day/years= 0.1/60/60/24/365/75 = ~4*e-11 ratio of blinks to years alive

Age of universe is 14Byears

14,000,000,000 * 4*e-11 = 0.59 years.

A cosmic blink is about 7months

Thanks that's actually an amazing perspective. Universe, after all - isn't that old if you think about it.

Especially not in relation to how old it is expected to become

That’s one possibility for the Fermi paradox. We might just be the first technological civilization in our neighborhood.

A trillion years from now this place might be packed with them (red dwarf stars, the most common type of star live about two trillion years, unlike our hotter, larger star.)

> Age of universe is 14Byears

It's age now. What will its age be when it is the relative equivalent of a 75yo human? A cosmic blink will be far longer than 7 months.

i don't think there really is such a relative equivalency. the universe according to best current understanding doesn't have anything which resembles human death to demarcate a lifetime. you could say 'heat death' but i dont think thats a strong comparison because, very much unlike human death, its a state which is approached asymptotically; the universe at heat death will look very much like the universe half way to, or even a millionth of the way to

I suppose the closest would be the point at which multicellular/intelligent life becomes impossible, or perhaps when all life becomes impossible. Stellar formation will end in about 100 trillion years, so that seems a good point.

For reference, the Appalachian mountains are older than this.

Sharks are older.

That’s the one I always like to pull out - if prehistoric sharks had telescopes with which to search the night sky, they would have seen Saturn without its rings.

400 My is almost 10% of the age of the Solar System. Definitely not a blink of an eye.

The total lifetime of the universe will be hundreds of trillions of years, which is perhaps a better scale to compare against.

Should read “in what amounts to a quick commute in cosmic terms”.

More like a year in the life of the cosmos.

Maybe people spend about a year of their lives commuting. If you commute an hour a day, every weekday, for 40 years, that’s 10400 hours, compared to the 8760 hours in a year.

“A quick commute” != “The accumulated time of one’s life spent commuting”

Here's another factor: over 4.5 billion years we really don't have a good idea of what close neighbours the Solar System has had. Stars are orbiting the Milky Way and I seem to remember reading not that long ago (hundreds of thousands of years) our closest neighbour wasn't Proxima Centauri but some other star that is now further away.

What other neighbours have we had? How bright have they been? How close have they been? Could they have been bright enough to melt ice? If so, would this impact the dust layer? Could they be massive enough to disrupt the "dusting"?

None close enough to have any effects like that. If there had been any close enough to have a gravitational influence the planets orbits would be either super scrambled up, or they would have gotten yeeted off into interstellar space.

"Close" in terms of stars is still super duper far apart.

We know close stars back 4 million years, and 5 million years in future. The closest known was 0.17 at 1.2 million years ago. That is close enough to disturb Oort Cloud but not be more than bright star.

I’m amazed that can go back that far with Gaia satellite data. There is a limit where the stars involved are too far away.

The ancient cultures an every habitual continent astronomically identified their "gods" as Mars, Venus, and Saturn. Why did they do that?

It was an inside joke, we don’t get it anymore.

I had always heard they were thought to be much younger than this new number. https://astronomy.com/news/2019/01/saturns-rings-are-surpris...

Yeah, 400 My is definitely on the older side of these "young rings" estimates.

Funny how the old Hebrew word for sun is Shemesh, and the Sumerians astronomically identified Shemesh as shown on the tablets of Shemesh as the planet Saturn. Huh. Weird. Wonder why they would do that.

In 1610, Italian astronomer Galileo Galilei first observed the features through a telescope, although he didn’t know what they were. (Galileo’s original drawings make the rings look a bit like the handles on a water jug).

They are made mostly of ice, which I didn't know, and may be raining down onto the planet. They could disappear in 100 million years.

Surely they must be raining down on the planet unless there’s an energy input from somewhere.

Why do you say that? The moon isn't raining down on us, it's actually slowly drifting away. Is there a reason they couldn't be in a stable orbit?

The Moon is not drifting away, it's been thrown away by tidal interactions. The Earth's spin is slowing down and the moon is accelerating. Energy is going in to the Moon's orbit and coming out of Earth's angular momentum.

My intuition is that without other sources of energy in the rings would decay eventually due to bits of them hitting each other occasionally, thus diverting some of them enough to interact with Saturn's atmosphere. Maybe there's some very small friction with gas from Saturn as well.

The main point is that when anything diverts things down, the results are asymmetric with up, making down the overall trend.

But as the article says, there is considerable energy input, with sunlight adding electromagnetic excitement so that things are getting diverted by the planet's magnetic field.

For sure. Seems hard to say, I'll bow to anyone's superior knowledge since I'm speculating right now, but I reckon a ring system may sometimes be a sort of natural optimizer which finds a stable configuration where they're far enough away to avoid the atmosphere and sparse enough that the effects between particles are negligible. The mechanism I propose here is that the most unstable parts of the system might deorbit first, leaving behind something stable.

Again, wanton speculation from someone on the internet who's qualifications are that they thinks this is an interesting question to consider, don't take it anymore seriously than that.

Yes, that's true. Saturn's gravity is slowly pulling the particles in the ring. In a few million years, the rings will completely disappear. Source -- StarTalk podcast (https://drpawd.com/search?query=are+saturn%27s+rings+falling...)

which makes me think, what a spectacle it must have been 200-300 million years ago

If we blow ourselves up, will all of the junk we left in orbit around the earth eventually form rings of garbage?

The Wall-E Hypothesis

No, the vast majority is in LEO and will drop in a few decades.

The Geo sats will stay up for millions of years though. The graveyard orbits, just a few hundreds of km above Geo, brushes up on ten million years from what I've been told. I can not actually find a reliable source online that gives any number.

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