00:00Our Sun might have a long-lost twig in the Milky Way.
00:03We'll never find it, but the evidence for it could be all around us.
00:12Our solar system is surrounded by something called an Oort Cloud,
00:16a vast region full of ice and debris that's much bigger than the region that includes all the planets.
00:23It extends halfway to the nearest star. It has 100 billion objects in it, researchers think.
00:30But the Oort Cloud is sort of difficult to explain.
00:34All of the planets and most of the asteroids in our solar system basically exist on a single disk, a
00:40flat plane.
00:41And the reason for that is that they formed out of a disk-shaped cloud.
00:45So they're all kind of on a line with each other.
00:48But the Oort Cloud isn't on that plane. The Oort Cloud is a sphere.
00:52And we know it's a sphere because the evidence for it is all the comets that come out of the
00:57Oort Cloud and into our solar system.
00:58And they come in from just all sorts of directions.
01:02But there's no good way, based on models of how our solar system formed, to really explain how all those
01:09objects got there and got into that arrangement.
01:12Avi Loeb, a researcher at Harvard University, known for wild and exciting ideas about how space works,
01:18wrote in a new paper with his student Amir Siraj that that Oort Cloud, that vast sphere, that mysterious vast
01:25sphere full of stuff we can't explain,
01:27might be a footprint of a long-lost binary twin of our sun.
01:31Now, binary stars are pretty common in space.
01:34Two stars just that form together or get captured by one another and end up orbiting around each other, orbiting
01:40a common point between them.
01:42And if our sun had a binary twin when it was born in this birth cluster full of stars that
01:49gave birth to our sun and many other objects and would have been full of stuff,
01:54working together, their gravity would have done a much better job of collecting debris into an Oort Cloud around each
02:02star.
02:03At least that's what Loeb says.
02:05Now, we don't know for sure if this binary twin existed, but Loeb said it would do a much better
02:11job of explaining the Oort Cloud
02:14than any models of how our solar system evolved that just have the sun by itself.
02:20The good news is that there's actually a way to test whether this is true.
02:24One of the reasons that Loeb began wondering about this is a lot of scientists believe that there's actually a
02:30ninth undetected planet
02:31in our solar system drifting somewhere way out beyond Neptune, deep in the solar system, in the region of the
02:38Oort Cloud.
02:39And the reason scientists think this is that objects beyond Neptune are sort of clustered as if there's some sort
02:47of tugboat out there
02:48pulling them into formation with gravity.
02:51Now, if that's true, if there's a big, heavy planet out there, and it would be pretty heavy,
02:56I just think it has like five to ten times the mass of the sun, then that's even harder to
03:02explain.
03:02How did a planet get out there so far beyond the disk that formed all the other planets?
03:08And Loeb said that if the binary hypothesis is true, then Planet Nine didn't originate in our solar system.
03:16It probably originated somewhere in the cluster of stars where a sun was born,
03:20and our sun working together with its binary twin might have captured it.
03:25But it wouldn't have just captured Planet Nine.
03:27It would likely have captured many, many other dwarf planets,
03:32you know, small planets that don't quite reach the full planet classification,
03:36but are on the size of Pluto or Ceres or these objects we do see around our solar system.
03:42And if there are lots of dwarf planets out there in the Oort Cloud,
03:45there's really no way our sun could have done that on its own.
03:49It would have needed a binary twin, at least according to Loeb,
03:52to capture such a wide array of planets.
03:55Right now, Planet Nine has not been directly detected,
03:58and there's no evidence for these other dwarf planets.
04:02But Loeb said that future telescopes, particularly a telescope called the LSST,
04:07that are coming online in the next few years,
04:10that are going to do a really good job of doing big scans of the sky,
04:14might be able to detect not just Planet Nine, but also these other dwarf planets,
04:19these dim, dim points of light drifting in this vast region of space.
04:23And while that wouldn't 100% prove that our sun had a binary twin,
04:27it would be very strong suggestive evidence.
04:30So right now, have we proved that there's a twin?
04:35No.
04:35Do we know where it went?
04:36No, but probably another star came by and knocked it out of orbit with our sun.
04:41And we'll probably never find it.
04:43So much time would have passed, billions of years since our sun lost its twin.
04:48And they're probably in totally different parts of the Milky Way at this point, Loeb said.
04:52But we might be able to show that it was once there.
04:55That's pretty cool.
04:56Don't let me know.
04:59I love it.
05:01That's pretty cool.
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