Placeholder Image

字幕表 動画を再生する

  • This episode is supported by Cheddar.

  • [♪ INTRO]

  • When astronomers look out into the galaxy, they see all kinds of planets orbiting other stars.

  • But the most common type might be the worlds the size of our solar system's ice giants, Uranus and Neptune.

  • And that's great! It means we have two prime examples right in our own backyard,

  • so we can take a close-up look at what these exoplanets might be like.

  • Unfortunately, we know less about Uranus and Neptune than almost anywhere in our solar system.

  • Which is not so great.

  • We've already done an episode about Neptune and its mysteries, so let's jump back and

  • check out three of our biggest, seemingly most basic, questions about Uranus.

  • The first question is one astronomers have been asking for decades:

  • Why is the planet lying on its side?

  • Relative to the plane of its orbit around the Sun, Uranus is tilted about 98°,

  • four times more than Earth.

  • What's more, whatever happened must have occurred early on because the planet's rings

  • and moons are tilted by the same amount.

  • The accepted idea is that, during the solar system's early days,

  • Uranus was hit by an object several times larger than Earth.

  • That knocked the young planet over, and the moon- and ring-forming

  • disk that surrounded it followed suit.

  • But a giant impact is kind of the default theory in planetary science.

  • Some computer simulations published in 2011 suggest it might have actually taken more

  • than one impact to create what we see today.

  • And one 2009 paper points out that a collision might not have been necessary at all.

  • If any evidence of what truly happened still survives, it's probably deep within the

  • planet's interior, hiding under all those smooth outer layers.

  • The only way to figure out what's down there is through gravity measurements,

  • and those can only be made by a spacecraft in orbit.

  • As the satellite circles Uranus, the extra gravity from denser areas would speed it up

  • a tiny bit, while less dense areas would slow it down.

  • Over time, the pattern of these changes could hint at the planet's internal structure.

  • And if Uranus seems weirdly lumpy on the inside, it might give us clues about its ancient past.

  • Amazingly, the planet itself might not have had the Uranian system's most troubled past.

  • That honor could belong to its moon Miranda,

  • which appears to be among the solar system's most tortured objects.

  • Less than 500 kilometers across, Miranda has canyons more than 20 kilometers deep.

  • It's covered in cracks, and its surface seems to have been pushed and pulled from all directions.

  • To top it all off, its orbit is also tilted relative to Uranus's equator over ten times

  • more than any of its other major moons.

  • There are all sorts of hypotheses about what might have happened, from yet another impact

  • to tidal heating and gravitational interactions with the other large moons.

  • But all planetary scientists have to go on is a few images from the Voyager 2 spacecraft in 1986.

  • And those are on just one side of Miranda.

  • A long-term Uranus orbiter could build a global map of the moon's surface, which would enable

  • geologists to reconstruct the order in which these different events must have occurred.

  • Finally, lots of pictures could also help solve the case of the weird Uranian rings.

  • Today, we know of 13 of them, and they're pretty cool by themselves.

  • Some are dark, and others have hints of color like red and blue.

  • One even seems to contract and expand, about five kilometers over a few hours.

  • They're very different from the rings around Saturn.

  • Instead of being broad and icy, Uranus's rings are narrow and dusty.

  • The dust is probably bits of rock knocked off nearby moons by meteor impacts, but no

  • one's really sure why the rings are so narrow.

  • Normally, as ring particles bump into each other,

  • they tend to spread out in a process called diffusion.

  • One way of confining that material into a narrow ring

  • is through a pair of moons, called shepherd satellites.

  • One shepherd orbits inside the ring and one outside, and together their gravity keeps

  • the band trapped in a narrow region.

  • That's the case for one of Saturn's rings, but only one of the many narrow Uranian rings

  • seems to have its own shepherds.

  • We're not positive what's going on with the other ones.

  • Of course, it is possible that astronomers just haven't found all the moons that are out there.

  • When the Cassini spacecraft arrived at Saturn, it found many new moons,

  • including one embedded directly in the planet's rings.

  • And back in the '80s, Voyager 2 found ten Uranian moons of its own.

  • An orbiter at Uranus might turn up a similar collection and, even if it doesn't, long-term

  • observation of the rings's motion could help scientists figure out what's going on.

  • Now, if you've been paying attention, you might have noticed I've said one word

  • over and over again: orbiter.

  • That's the key to solving these mysteries and many more.

  • Only with careful, repeated observations can researchers build a complete picture of what's

  • going on in the Uranus system.

  • And only an orbiter can make that happen.

  • The good news is, that's exactly what planetary scientists plan to do.

  • Every ten years, the research community gets together to create a roadmap for the coming decade.

  • And in their most recent version, which was released in 2011, a mission to Uranus was

  • listed as one of the most important objectives.

  • Of course, that's no guarantee, and even if a mission started development tomorrow,

  • we'd still be many years from launch and many, many years from getting results.

  • But things are moving in the right direction.

  • And that's critical, because understanding Uranus isn't just about our own solar system.

  • It could be key to the history of planets all over the galaxy.

  • Thanks to Cheddar for supporting this SciShow Space video.

  • If you subscribe to SciShow Space, you might also really like Cheddar, which recently launched

  • their YouTube Channel where they make videos that cover

  • science, technology, innovation, business, and news.

  • I just watched their video about the best-case asteroid hitting Earth scenario,

  • which sounds like a bad day, but it's a really fun video.

  • I learned about the difference between an asteroid hitting land vs. water, and how to

  • embody Bruce Willis and his roughneck pals when it comes to the potential end of the world.

  • Check out all their videos at YouTube.com/Cheddar,

  • and we'll link to the asteroid video in the description.

  • [♪ OUTRO]

This episode is supported by Cheddar.

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

天王星を倒したのは何だったのか?他の二つの謎 (What Knocked Over Uranus? And Two Other Mysteries)

  • 1 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語