Placeholder Image

字幕表 動画を再生する

  • This episode is sponsored by The Great Courses Plus.

  • [♪ INTRO]

  • Saturn's beautiful rings might be the most recognizable thing in all of astronomy,

  • but it won't be that way forever.

  • In 2018, planetary scientists realized that the rings

  • are disappearing way faster than previously expected.

  • In fact, some researchers went as far as to say this was theworst-case scenario.”

  • Now, before the wave of grief overwhelms you, remember that this is astronomy.

  • In this case, “way fastermeans that the rings may only be around for another

  • hundred million years or so.

  • What might be even more surprising about this research is that it suggests Saturn's rings

  • might also only be around a hundred million years old,

  • billions of years younger than some astronomers have suspected.

  • That complicates our understanding of where the rings might have come from in the first place.

  • And it's making some people wonder if, maybe, the ring system we see today

  • isn't the only one Saturn has ever had.

  • Those 2018 results were thanks to NASA's Cassini mission, which wrapped up in 2017.

  • As the mission came to an end,

  • scientists sent the spacecraft between Saturn and its rings for the very first time.

  • During these final orbits, Cassini detected material falling from the innermost ring onto

  • the planet's upper atmosphere, the first direct measurements of what scientists called ring rain.

  • And the data were backed up by astronomers using the giant Keck telescope in Hawaii.

  • Material falls from the rings for a bunch of reasons, including random collisions between

  • ring particles and particles getting dragged around by Saturn's magnetic field.

  • We've actually seen evidence of this process since the 1980s,

  • so that part of Cassini's discovery wasn't surprising.

  • What did catch scientists off guard, though, was how effective ring rain seems to be.

  • Cassini and Keck's observations allowed scientists to more accurately calculate the

  • rate Saturn's rings are losing material, and they found it could be anywhere from around

  • 5,000 to 45,000 kilograms per second.

  • And that has some significant implications.

  • Researchers have used that new number to run time forward and backward in computer simulations,

  • and they've found that it would only take around a hundred million years

  • for what we see today to disappear.

  • But even more significantly, you'd only have to go back about a hundred million years

  • for Saturn's inner rings to have as much material as the largest one does today.

  • Scientists think that's a pretty good estimate for how old the ring system might be.

  • It's a rough guess, but that value matches other lines of evidence,

  • like how clean the rings seem to be.

  • Either way, what's clear is that the rings are young compared to the four and a half

  • billion-year age of the solar system, and that kind of throws a wrench in things.

  • See, Saturn's rings are the outlier in the solar system.

  • Not only are they much larger than those of other outer planets,

  • but they're also made of nearly pure ice instead of dust and rock.

  • Whatever formed them needs to account for this purity.

  • And that eliminates many options, since most objects in space contain a mix of ice, rock, and metal.

  • The problem is, some of the best hypotheses that do explain the

  • purity really only make sense if the rings are as old as the solar system.

  • Like, one idea is that the rings are the icy outer layers of a large moon

  • that was torn apart by Saturn's gravity.

  • But in order for a moon that size to get close enough to Saturn to be ripped apart,

  • there would have to be a disk of debris around Saturn,

  • and that disk only lasted a short time after the planet formed.

  • Another possibility is that a large asteroid or comet destroyed a medium-sized moon like

  • Mimas, which contains very little rock or metal.

  • But again, that kind of big collision was much more common billions of years ago

  • than a hundred million years ago.

  • Researchers aren't totally out of ideas, though.

  • One hypothesis that might make more sense is a pair of smaller moons colliding in

  • the recent past, similar to how some scientists think the rings of Uranus formed.

  • The gravity of a passing comet might be enough to nudge one object into the orbit of another,

  • and most of Saturn's small moons seem to be nearly pure ice, anyway.

  • Unfortunately, the models for this idea aren't all that supportive so far,

  • so it might be back to the drawing board.

  • Scientists will likely be researching their hypotheses for a while,

  • but there's actually another, even bigger question raised by Cassini's discoveries:

  • If the rings are so young and short-lived,

  • why are we so lucky that we get to be around when they are?

  • Astronomers hate feeling lucky, because it sometimes means

  • that they're not looking hard enough for the deeper answer.

  • So many don't think this is a coincidence.

  • Like, maybe these rings are recent, but what we see is actually just the latest iteration

  • of a process that has happened multiple times in Saturn's history.

  • Maybe Saturn has spent the last four billion years collecting and destroying one ring system after another.

  • If that's true, it might also mean that the other outer planets have had large rings

  • in the past, too, but they just don't right now.

  • There are a lot of questions left to answer here, but they're ones scientists are actively

  • investigating, and they could lead to a new understanding of how ring systems form,

  • and what our solar system looked like not that long ago.

  • Oh, and in case you're still mourning the future loss of the rings,

  • there is one last bit of good news: Even once the main rings have disappeared,

  • Saturn won't be entirely ringless!

  • The dusty G ring and Phoebe ring are constantly being replenished by debris knocked off nearby moons,

  • and the E ring is composed of ice particles ejected by the geysers on Enceladus.

  • So there still will be rings! Everything will be alright.

  • And who knows, maybe by then another planet will have some new bling to show off!

  • If you're interested in learning more about space science and how to understand it,

  • you can check out The Great Courses Plus!

  • It's a subscription-based, on-demand video learning service,

  • and it is full of some seriously impressive lectures and courses.

  • You can watch a lecture from professors at Ivy League universities,

  • other great schools worldwide, or experts from places like National Geographic,

  • The Smithsonian, and the Culinary Institute of America.

  • They have more than 11,000 video lectures to choose from, and you can learn just about anything.

  • They have courses on science, math, history, literature,

  • and even hobbies, like cooking or photography.

  • If you want learn more about the inventions that have helped us explore space,

  • you could watch a course called Space, Technology, and Discovery.

  • It opens with an episode about the Curiosity rover, so you know I am immediately on board.

  • Right now, The Great Courses Plus is giving SciShow viewers the chance to try their content for free!

  • And if you choose to subscribe after the trial, you will be supporting SciShow, too.

  • To learn more, you can visit thegreatcoursesplus.com/SciShowSpace,

  • or click the link in the description to start a free trial.

  • [♪ OUTRO]

This episode is sponsored by The Great Courses Plus.

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B1 中級

土星には複数のリングシステムがあった? (Has Saturn Had More than One Ring System?)

  • 2 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語