The Oort Cloud: Crash Course Astronomy #22


Well, look where we are now. With our backs
to the Sun, and the planets, asteroids, and comets behind us, we face deep space. There’s
nothing between us and the stars, so terribly terribly far away. … or is there? The empty space past Neptune isn’t exactly
empty. In episode 21 I mentioned that comets come in two varieties: Those with orbital
periods of less than 200 years, which tend to orbit the Sun in the same plane as the
planets, and those with longer periods, which have orbits tilted every which-way. This is something of a problem: Comets lose
material when they get near the Sun. Over the course of millions of years these comets
should evaporate! And yet here we are, 4.56 billion years after the solar system’s birth,
and comets still appear in our skies. So, where are they coming from? To see, we’ll have to turn the clock back
a wee bit – like, 4.5 billion years. Behold, our forming solar system. Coalescing
out of a flat disk of material around the Sun, the inner planets were warmer, smaller,
and rocky, while the outer planets were in a region that was colder, and grew huge. Out
there in the chillier part of the solar system, water came in the form of ice mixed in with
dust and other stuff. These bits would collide and stick together, growing bigger. Some grew
to hundreds of kilometers across. But there was a problem: those outer planets.
They had a lot of gravity, and any chunk of ice getting too close would either fall into
the planet and get assimilated or get kicked into a different orbit. It could then plunge in toward
the Sun, or get flung out into deep space. Trillions upon trillions of such iceballs
got tossed around by the planets. Even though they were small compared to the planets, they
did have a little bit of mass and gravity, so every time the planet pulled hard on them,
they also pulled a little bit on the planets, too. It wasn’t much per chunk, but after
trillions of events this adds up! A current model of what happened, called the Nice model
after the city in France where it was proposed, says that the overall effect of all these
encounters was that Saturn, Uranus, and Neptune slowly moved outward from the Sun, while Jupiter
moved inward. Neptune would have had the biggest effect
on these iceballs, because it bordered the biggest volume of space where they lived.
As Neptune migrated outward, close encounters with these chunks of ice flung lots of them
into crazy orbits, highly elliptical and tilted with respect to the planets. Repeated more
distant encounters tended to more slowly increase the sizes of the orbits of the iceballs, too. We think that this shuffling around of the
outer planets is what caused the Late Heavy Bombardment, the intense shower of objects
that came screaming down from the outer solar system, scarring planets and moons, a few
hundred million years after the planets themselves formed. It’s not known for sure, but all
the pieces fit together really well. In the end, today, there are three rather distinct
populations of these objects. One is a region shaped like a puffy disk or a doughnut, aligned
with the plane of the planets. Icy objects there have stable orbits, unaffected by Neptune.
We call this the Kuiper Belt, named after the Dutch astronomer Gerard Kuiper, one of
many who initially speculated about the existence of this region. The Kuiper Belt starts more
or less just outside Neptune’s orbit, extending from about 4.5 to 7.5 billion kilometers from
the Sun. The second region is called the scattered
disk. This is composed of the iceballs sent by Neptune into those weird, highly tilted
orbits. This overlaps the Kuiper Belt on its inner edge, and extends out to perhaps 150
billion kilometers from the Sun—that’s 25 times farther out than Neptune. Finally, outside those two zones there’s
a spherical cloud of icy objects which starts roughly 300 billion kilometers out— 70 times
farther out than Neptune, a staggering 2000 times the distance of the Earth from the Sun.
And that’s just where it starts: It extends way farther out than that, perhaps as much
as a light year, 10 trillion kilometers! This is called the Oort Cloud, after astronomer
Jan Oort who first proposed it. The Oort Cloud is the origin of long period
comets. Since they orbit the Sun on a sphere with no preferred orientation, they come in
toward the inner solar system from random directions in the sky. Many newly discovered
comets fall into this category. Their orbits can be extremely long; they start their fall
from so far away they swing around the Sun at nearly escape velocity, and their orbits
are close to being parabolic. The scattered disk is the source of short
period comets. They can still be affected by Neptune, which can alter their orbits to
drop them down closer in. They can orbit the Sun on paths between Jupiter and Neptune,
meaning eventually they’ll have a close encounter with Jupiter. This can send them in closer
to the Sun, and they become short period comets. Tadaaa! That’s how comets are made. So how do we know all this? Well, until 1930
it was pretty much just conjecture. But then an American astronomer, Clyde Tombaugh, discovered
the first Kuiper Belt Object: Pluto. Pluto orbits the Sun on an elliptical, mildly-tilted
path. Its orbit actually brings it closer to the Sun than Neptune! So how come it never
collides with the larger planet? Pluto’s orbit crosses Neptune’s… more
or less. Because the orbit is tilted, they never actually physically cross. When Pluto
is at perihelion, closest to the Sun, it’s well above the plane of the solar system,
far from Neptune’s orbit. Not only that, but Pluto orbits the Sun twice
for every three times Neptune does. Because of this, whenever Pluto is closest to the
Sun, Neptune is always 90° away in its orbit. That’s many billions of kilometers distant,
way too far to affect Pluto. This is mostly coincidence. We’ve seen how
orbital resonances can be forced by tides and by gravity. But in this case it’s due
to attrition. Once upon a time, billions of years ago, there were probably a lot of objects out by
Pluto, with orbits of all different shapes and tilts. But the ones that got too close to Neptune
got gravitationally tweaked into different orbits, turning them into comets or flinging
them deeper into space. The only ones that could survive just happened to have orbits
with that 3:2 or 2:1 resonance with Neptune, keeping them far from Neptune’s influence.
Today, those are the only kinds of objects we see with orbits near Neptune. We call these objects plutinos. They’re
not really a separate class of object—they’re still Kuiper Belt objects, but a fun and interesting
subset of them. Once Pluto was found, astronomers wondered
if it might herald a new class of icy objects past Neptune. However, it took more than six
decades to find the next one! 1992 QB1 was discovered in 1992, and that opened a sort
of gold rush of Kuiper Belt discoveries. We now know of more than a thousand Kuiper Belt
Objects. One, called Eris, is very close to Pluto’s size and is more massive — it’s
probably rockier than icy Pluto. Pluto is an interesting object. A moon was
discovered in 1978. Named Charon, it’s actually about 1/8th the mass of Pluto itself! While
Charon orbits Pluto, the moon has enough mass that it can be said that Pluto noticeably
orbits Charon, too. In reality, both circle around their mutual center of mass, located
between the two. Four more moons were discovered in Hubble
images of Pluto in 2005 and 2012. There may be more. Pluto is so small and distant that we don’t
know much about it… but that may be about to change. [sighs] And now I have to admit to being in a tough
spot. As I record this episode of Crash Course, a space probe called New Horizons is heading
toward Pluto. It will fly by the tiny world in July 2015. There’s no doubt our view
of Pluto will change: There may be more moons discovered, we’ll see surface features for
the first time, and much more. But right now I can’t tell you about any of that because
we don’t know yet. So I think the best thing to do is leave little Pluto alone for now. But there is a point I want to bring up. Pluto
was found in 1930, long before any other Kuiper Belt Object, because it’s much brighter
than any other. When it was discovered, it was thought to be about the size of Earth.
But over the years better observations showed it to be far smaller than first thought; in
fact it’s smaller than Earth’s Moon! Its surface is unusually reflective, shiny, making
it look much bigger than it seems. Most other Kuiper Belt denizens are far less reflective,
and so are far fainter. If Pluto is King of the Kuiper Belt Objects,
it has a lot of loyal subjects. We think the Kuiper Belt may have 100,000 objects in it
larger than 100 km wide. If that sounds like a lot, get this: The Oort Cloud, surrounding
the solar system, may have trillions of icy bodies in it. Trillions! While we know of lots of Kuiper Belt Objects,
we don’t know of any Oort Cloud objects for sure. Two very interesting bodies have
been found: Sedna, and VP113. Sedna’s orbit takes it an incredible 140 billion km from
the Sun, while VP113 gets about half that far out. Both are on very elliptical orbits.
Neither, however, gets close to Neptune, so it’s not at all clear how they got where
they are. They may be Oort Cloud objects that were disturbed by passing stars long ago, dropping
them closer into the Sun. But no one knows. Yet. Speaking of which… we can calculate how
many Oort Cloud objects there should be left over from the formation of the solar system,
and it’s about 6 billion. However, calculating how many there are using long period comet
observations, you wind up getting about 400 billion. That’s a big discrepancy! Now get
this: One idea to solve this discrepancy is that the Sun has stolen comets from other
stars. Seriously! Comets should form wherever stars do, and sometimes the Sun passes near
other stars. When we see a long-period comet gracing our skies, could we be seeing an object
from an alien solar system? Maybe. There is another explanation, but it’s highly
speculative. Perhaps there’s another planet in the solar system, well beyond Neptune. It’s possible. Some very preliminary studies
have shown that some long-period comets aren’t coming in randomly, but instead have their
orbits aligned in a way you might expect if a very distant planet perturbed them. There are a
handful of Kuiper Belt Objects aligned in a similar way. NASA’s WISE observatory scanned the skies
in infrared, and would’ve seen anything as big as Jupiter or Saturn out to tremendous
distances, so any hypothetical planet would have to be smaller. And very distant, probably
tens of billions of kilometers out. We’ve seen other stars with planets this far out,
so it’s physically possible. But is there one really there? We can’t
say either way, yes or no. At least, not yet. This region of the solar system is seriously
underexplored. It’s distant, difficult to reach, and above all else extremely huge and
numbingly empty. You could hide a whole planet out there, and it would be pretty hard to
find. The point? There’s still lots of solar system
left to explore. We’ve barely dipped our toes into these dark, frigid waters. Today you learned that past Neptune are vast
reservoirs of icy bodies that can become comets if they get poked into the inner solar system.
The Kuiper Belt is a donut shape aligned with the plane of the solar system; the scattered
disk is more eccentric and is the source of short period comets; and the Oort Cloud which
surrounds the solar system out to great distances is the source of long-period comets. These
bodies all probably formed closer into the Sun, and got flung out to the solar system’s suburbs
by gravitational interactions with the outer planets. Crash Course Astronomy is produced in association
with PBS Digital Studios. Mosy on over to their channel because they have even more
awesome videos. This episode was written by me, Phil Plait. The script was edited by Blake
de Pastino, and our consultant is Dr. Michelle Thaller. It was directed by Nicholas Jenkins, the
script supervisor and editor is Nicole Sweeney, the sound designer is Michael Aranda,
and the graphics team is Thought Café.

Author Since: Mar 11, 2019

  1. It really confused me that you had the Mystic mountains in the background when introducing the Oort cloud 4:01. I thought I was mistaken in thinking that was a distant object and that it was actually a part of our solar system and had to google it to prevent my misunderstanding.

  2. We now know that Pluto has five, not more moons, and is icy. New Horizons showed that it was indeed a dwarf planet, smaller than Earth's moon, but is bigger than Eris, which is more massive. New Horizons' flyby sent it following in the wake of Voyager 1 into the Oort Cloud, where the comets Sedna and VP113 hide from us. What will New Horizons send back to Earth then? Will we find extraterrestrial life?

  3. Planet X has been recently discovered, but ever since Pluto got demoted, some astronomers are calling it Planet IX, Roman for Planet 9.

  4. Is it true that all the objects in the
    Oord Cloud are comets? Aren't
    some of them asteroids?

  5. Additional fact: Eris's orbit is so eccentric that its perihelion occurs in the Kuiper belt, however it is generally considered to be an object of the much further out scattered disc.

  6. The galactic tides also have a nice effect on Oort cloud obejcts and to certain extent scattered disk objects. They can effectively change the eccentricity of an orbit. Objects orbiting near the outer part of the hill sphere of the Sun are very prone to gentle "impulses". Especially when those "impulses" take place over milion and milion of years and happen periodically. The material there just come and go. Any gentle gravitational (or even nongravitational) pull or push can change the eccetricity of orbits there.

  7. There are likely whole geologically active planets living in the Oort cloud. Just being so far from the sun they don't reflect the light anymore. They would be rocky planetoids since there's very little gas out that far.

  8. Geez, I’m only 50 yrs old and the solar system is so different then when I went to school. There was the nine planets including pluto. But we had to memorize all the names of the moons around each planet. Which was easy because there were only a few known at the time. What ever happened to the astroid belt? When I was in school they told us that we passed through it twice a year. I think it was about 3 months apart and during that time if you went outside you would see a lot of shooting stars. That must still be there between Mars and Jupiter because how could it not be. But what I don’t understand is why it is never, ever mentioned in any videos. Why don’t they ever mention it anymore? They talk about the kiuper belt constantly which barely ever effects us. Whereas the astroid belt you can go outside and see so many shooting stars while crossing it. Is there something about the astroid belt that I don’t know about?

    This younger generation and the ones after it are so lucky to have current information on everything right at there finger tips. There was a time when you were at home and if you had a question you had to hope your parents knew the answer and being that older generations are less educated you probably didn’t get an answer. Your next option was to look in a set of encyclopedias. Not many had encyclopedias in their home because they were so expensive. You had to go to the library. However, by the time you usually made a trip to the library you had already forgotten your question. Worse then that is that the information on a particular subject in the encyclopedia was maybe a half a page in bigger font then we use today with a drawing or picture on the top half. That’s not a lot of information to know about your subject. When we did little research projects for school we always had to include a newspaper article as a source. Very different from today. Today’s technology is so wonderful and amazing. I wish I could live forever to see all the knowledge and technology that is still to come. I want to know what the next unknown-unknown will be. Sort of how electricity changed the world forever. There has to be more crazy physics out there that we just haven’t stumbled upon yet that will change the world forever again. And then again and again. So amazing.

  9. The mere hypothetical coincidental construction of our solar system and how all of it together might be what made life has gotten me more interested and wanting to study the thought and everything involving it

  10. I've saw jupiter and staurn in the night sky once and omg I dunno which one was brighter I countd tell

  11. You need to think of standardizing your use of measurements. You seem to use whatever system gives a larger factor of basic measurements for dramatic effect.

  12. Who are we? Why we came to existence? When and how long it took to create life? All these questions were answered in a book 1400 years ago. The Quran. Reading a book cannot harm you. Good luck.!

  13. Who thought there's nothing past Neptune? I was thought there is a planet called Pluto at least with some asteroids. Then they found Kyper belt. And revoked Pluto it's planet's card. Shame… But never mind, it's called the half-life of the facts.

  14. I read that no one is actually 100% sure the Oort Cloud actually exists…so when they say “we know this” and “we know that”….they really don’t know…they’re just guessing and guessing and the best guess of the time gets generally accepted until it is inevitably disproven within a decade or two…50 years ago science claimed “Saturn is the only planet with rings”….well I think we all know how that turned out. It’s hard to not be skeptical about all these new discoveries science and astronomers are making when they get disproven or rearranged within only a few decades. The only path to knowledge is to know that we know nothing…..

  15. Oort cloud is just a guess. No one knows for sure. As far as I'm concerned, it doesn't exist. Until we observe it.

  16. Outer planets:(opening a bag of taki's.)

    Random space objects: oh, can I have some.

    Outer planets: NO, now go away or i'll make you.

    Random space objects: but I want some chips.

    Outer planets: ok you ask for it.(throw object away from him)

    Random space objects: NO WWWWwwwaaaiiitttt!.

  17. We have evidence about what happens when a dwarf planet crosses Neptune's orbit.

    It's called Triton.

  18. Now we know what Pluto really looks like 😍 I wonder how Phil reacted to the first pictures 😁

  19. Great video, but you folks need to do an update to incorporate all the New Horizon's imagery and data.

  20. further data: The naming "Edgeworth comet disc" would rather match. The Irish astronomer Kenneth Edgeworth postulated that comet disc eight years before Mister Kuiper. The naming (Kuiper) belt must have come from when the comet disc wasn't yet distinguished=differentiated from the (inner) oort cloud which could be a halo-like hollow sphere of ices similar to the outer oort cloud. Most comets would gather there (scattered disk also is named similar) and it's (as far as discovered) flat instead of belt-shaped (excluding few comets with unusual orbits). Strong forces might have put those objects on resonnance whilst hardly any distortion occured. A lot of objects further off of Neptune are assumed to have gotten frozen 3 and a half billion years after the birth of our eight planets.

  21. I love that at 1:08 the image had a "Artist's impression of a protoplanetary disk" statement at the bottom.

  22. this is joe from the futer [well acording to video date] im looking at your video from 5 yrs in the past because citizens are scared and nasa and gov turned to the dark side so im a researcher volunteer to assist peoples answers on you tube channels as an assistant to many
    i understand if nirburu or nemessis isnt real but at least explain each 1 billion thimgs happening to earth that fits the bill of a pole shift planet crossing [many reports that scientist and media censored or ????? will happen to them if reported on incoming stars

  23. How about the difference between every comment nuclei ever pictured which looks like a hunk of rock throwing the whole 30 AC snowball theory of the window. It’s amazing how one or two things will be used to try and discredit plasma cosmology but the simple fact it not a single prediction of comments composition has ever been proven by direct observation is mine boggling that you still follow that Ludacris idea, 30 snowballs when you have absolutely no proof of that and there is absolutely no document a picture of a dirty snowball yet including Haleys comet

  24. There is a lot of old and wrong science here. If you viewers are really into science, you need to dig deeper for the truth. Don’t trust government funded science and education.

  25. There is no Ort cloud. And, 92% of the universes mass is not "dark matter". In reality, what some folks think is a cloud around the sun is just the constant state of interstellar space.

  26. If you were able to travel in space, and travel far enough, space is so vast that you would pass through the Oort cloud and not even see any of the Oort objects. Similar to the Asteroid belt, you would imagine that they would be clumped together, but they're not.

  27. I knew and worked for Prof. Oort at The Sterrewacht in Leiden. An amazing man who was not only a scientist but a politician, and believe it or not, an expert ice skater at age 65.

  28. To me New Horizons proved that Pluto is in fact a planet after all. And after all that hysteria about it so Whatshisface could get his Nobel prize and whatever.

  29. Fantastic video… however because the scientific method says that in order to be a fact it must be observed… how can this video act like the Oort Cloud is a scientific fact? It very well probably is… but it's never been observed

  30. "Saturn, Uranus and Neptune slowly moved outward from the Sun, while Jupiter moved inward." 2:10
    For real? How does that work?

  31. This video was released on 2015. Today in 2019 I don't know which all facts to take from the video. Please do an updation if any.

  32. Scientifically speaking, the Oort cloud is not a cloud at all. It is a belt. But a belt in three dimensions as it is not flattened by internal collisions.

  33. I remember the last time Haley's Comet passed by when I was in elementary school, and the teachers all made a big deal of it.

  34. Oh Horseshit;The OORT CLOUD does not exist! There has never been a shred of evidence supporting a comet birthing area called the Oort cloud! The Dutch astronomer Jan Hendrik Oort was trying to get his 15 minutes of fame. Do a little research and you will see the Oort Cloud is as factual as Big Helmet attaining PLAID SPEED!

  35. yup its 2019 and new horizons already passed pluto and ultima thule, not sure where its headed now but this is a great time for astronomy

  36. In 2046 you will get a new kind of crash course when the sun goes through is 12,068 year repeating catastrophe cycle and the expected micro-nova destroys almost all life on Earth and trashes all of the inner planets quite badly. One side is burned off of the Earth and the other side freezes instantly from the atmosphere being rapidly decompressed to the side of the planet where air used to be but no longer exists. All of the debris that is ripped off of the face of the Earth is sent hurling far out into the solar system, and all of that debris is what we now call the Oort Cloud. Sadly, I wish I was kidding…. but it is all too real. Oh… and that is also how the thousands of animals were FLASH frozen with fresh food still in their stomachs. Remember the Woolly Mammoth?
    Uh huh… Visit the Diehold Foundation for the proof. Our government has known since 1957. Why else do you think all of the Moon missions were named after a Sun god. They wanted to see if the sun also cooked the moon and they found it. So why go back? They didn't bother.

  37. I appreciate you listing the production crew, but noticed you left out who your camera team, lighting, and grip technicians were. If your going to give props, you'd look better to go all the way and give proper credit where it's due. It would be nice to know who is putting in the effort to make this great content become a reality. (*squints at the Green brothers, and coughs)

  38. I have a question: I know the Oort Cloud, and by extension, us, are orbiting Saggitarius A (Aka the black hole at the center of The Milky Way just like everything else in the Milky Way is) but:

    Is our sun itself orbiting around something else AS that object itself orbits around Sagitarius A?

    Essentially, does our sun have it's own orbit around something else within The Milky Way as we all orbit Sagitarius A.

    (I rephrase my question because somethings it's hard for people to understand what is meant, so I try to be as communicative as possible)

  39. Can we have another episode of crash course astronomy with new topics or updated information? I like this series very much.

  40. If our outer oort cloud is up to a light year in radius, that means that our oort cloud would overlap with alpha centauri, and could exchange oort cloud objects or even have objects with a binary orbit. Swinging around on the sun and out to AC then back again.

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