00:00Our solar system is full of mysterious objects that come from, well, everywhere. In October 2017,
00:07researchers in Hawaii spotted a mysterious thing that they dubbed a muamua.
00:12This means a visitor from a faraway land in Hawaiian. Or, that's a really big cow!
00:18It followed an escape orbit. It literally escaped from its planet's gravitational pull, like throwing a ball into space never to return.
00:26This meant that this weird thing arrived from somewhere outside of our solar system.
00:33There were tons of theories about what it was, from a simple asteroid to an extraterrestrial spacecraft.
00:39Scientists even thought it was a chunk of nitrogen ice from a Pluto-like planet.
00:44Its strange shape only added to the mystery. The big changes in the light curves showed that this thing could be either
00:51elongated like a tube or more flat like a pancake.
00:54This thing was unlike anything we've seen before. A muamua didn't behave exactly like a comet or an asteroid.
01:02Comets are icy and form bright tails when they pass near the Sun, while asteroids are basically just rocks and don't form tails.
01:09A muamua has no tail and doesn't release gas, like me.
01:13But it's not your average rock either. Its surface is very shiny, almost like polished metal.
01:19When it passed by the Sun, it sped up, like it had a rocket on it.
01:23And it wasn't the Sun's gravity that gave a muamua the sudden boost.
01:28Scientists aren't sure what caused it. So, what in the world was that thing?
01:34After years of study,
01:36scientists now think that a muamua is probably a comet with frozen hydrogen on its surface. This hydrogen reacted with sunlight,
01:44speeding up the comet and changing its path.
01:47A muamua likely got all that hydrogen from being exposed to tons of cosmic rays for a long time.
01:53It got some nice red tint from them as well.
01:56A muamua was a visitor from a young chaotic solar system where collisions and migrations happen all the time.
02:03Such systems often toss many small objects around.
02:07It might have been pushed out by a planet like Jupiter, whose gravity is so insanely strong that it can fling huge things into outer
02:14space. The same thing often happens with comets here.
02:18A muamua already left our solar system, although similar objects visit us sometimes, about once per year.
02:25To learn more about these mysterious guests,
02:28astronomers plan to send a probe to chase a muamua.
02:31We'll use Earth's and Jupiter's orbits to slingshot it fast enough to catch up with the comet.
02:36But some of the unexpected visitors stayed a bit longer.
02:42In October 2019,
02:44NASA's Hubble Space Telescope took a picture of a bluish comet trailing dust and gas.
02:50It was already in the solar system at the time, around 260 million miles away from Earth,
02:56somewhere between Mars and Jupiter. We saw the glowing dust surrounding it,
03:00but we couldn't yet see its nucleus since it's way too small.
03:04Well, small is relative here. The thing is about 3,200 feet across,
03:09which is like the length of nine football fields. In March 2020,
03:13Hubble images showed that a small fragment of the comet broke away from the nucleus.
03:18That means that the comet is very active, unlike a muamua.
03:23As we observed it further, we found that the nucleus is a loose mix of ice and dust particles.
03:29Its surface is also very similar to others, with rough areas and smooth blankets of icy, dusty debris.
03:36The comet was discovered by an amateur astronomer, Gennady Borisov. So it got the name Comet 2I Borisov.
03:44Congratulations!
03:45Scientists quickly confirmed it came to us from outside our solar system.
03:49And this thing sure was an enthusiastic tourist. It traveled at a breakneck speed of about
03:56110,000 miles per hour. That's fast enough to circle the Earth four times in just one hour.
04:01This visit was fascinating for several reasons.
04:04Most comets in our solar system come from the Kuiper belt or the Oort cloud.
04:09The Kuiper belt is a region of space beyond the orbit of Neptune.
04:13It's like a big distant ring around the Sun, filled with many small icy objects.
04:18All of them are ancient leftover pieces from the time when our solar system was still very young. The Oort cloud is much farther.
04:26It's like a giant bubble around the solar system, also filled with super old icy objects.
04:31Most long-period comets come from there. But where did the Comet 2I Borisov come from? We still don't know for sure.
04:39Scientists say that it likely formed in another star system,
04:43which could be either younger or older than our solar system. Would be weird if there was a third option, NASA.
04:49Anyway, it might have been kicked out from its home system, just like Oumuamua.
04:55Although Comet 2I Borisov is too small to hold on to its own atmosphere,
05:00it developed a coma when it approached the Sun. Now, coma is a funny name for that beautiful glowing cloud of gas and dust
05:07that surrounds the comet's nucleus. It forms when the Sun's heat causes the comet's ice to vaporize,
05:14releasing dust and gas into space.
05:16This one was friendlier than Oumuamua and gave us some more time to study it. As a result,
05:22we learned more about its cool unique traits. For example, it had never interacted with another star.
05:28But unfortunately, Borisov had to leave too. Now, it's on a path that will take it back into interstellar space.
05:36However, there are many more visitors to come, and you might have heard of this one.
05:41The Great Comet of
05:441996. That's what we called the Comet Hayakutake.
05:47It was also named after the astronomer who discovered it, Yuji Hayakutake. In a beautiful coincidence,
05:54it was discovered on New Year's Eve. On March 25th,
05:581996, this thing passed by incredibly close to Earth, only about 0.1
06:04astronomical units away, a bit farther than the Moon. It passed over the North Pole.
06:09This made it one of the closest comet encounters in 200 years.
06:14It was visible worldwide, and it looked very bright and beautiful in the sky,
06:18stretching out widely. And it didn't stay for one night only. It got more and more visible during March,
06:24becoming one of the brightest objects in the night sky by the end of the month. The comet only fully faded by the end of May.
06:32It's a long-period comet, which means it takes hundreds of years to orbit the Sun. The last time it visited was about
06:4017,000 years ago, and now its orbital period increased to 70,000 years.
06:45But don't be upset. There are other comets that will brighten our days and nights.
06:50Besides, some space objects prefer to stay around for longer.
06:55Now, there's this asteroid with a multi-syllabic name that, to pronounce, is above my pay grade.
07:01This name in Hawaiian means the mischievous one of Jupiter. Luckily, scientists had mercy on us and dubbed it BZ.
07:08Hey, speaking for all the other narrators, thank you!
07:12It's a small asteroid, only about 1.8 miles in diameter.
07:16You can guess from the name that it shares an orbit with Jupiter.
07:19But there's a cool catch. The asteroid moves in the opposite direction, which is known as a retrograde orbit.
07:26The unusual asteroid was discovered on November 2014. It orbits the Sun for about 11 years and 8 months,
07:34sometimes passing inside and outside of Jupiter's orbit.
07:38It's been this way for at least a million years, and it will remain so for about a million more.
07:43But why does it move so unusually?
07:48BZ might actually be an interstellar immigrant.
07:52Perhaps it passed by our solar system about 4.5 billion years ago, around the time when the Sun was just forming.
07:58Then it got captured by gravity, but saved its opposite orbit. Or maybe it came from the Oort cloud.
08:06Then it could get its weird orbit from the mysterious planet Nine, a hypothetical planet
08:11that's believed to exist in our solar system far beyond Jupiter.
08:15In any case, this asteroid gives us more insight into the history of the solar system
08:20and how organic materials can travel to us from outer space.
08:25Now, at any given time, there are thousands of objects in our solar system that come from outer space.
08:31They stay here for different lengths of time.
08:33But sometimes we get lucky, and they end up teaching us a lot about interstellar space.
08:42That's it for today. So, hey, if you pacified your curiosity, then give the video a like and share it with your friends.
08:48Or if you want more, just click on these videos and stay on the Bright Side.
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