Notre système solaire a reçu des visiteurs vraiment rares. Oumuamua a été le premier objet interstellaire connu à traverser notre système solaire, et les scientifiques pensent qu'il pourrait s'agir d'un astéroïde de forme étrange ou même d'un morceau de planète brisée. Puis, il y a la comète Borisov, une autre voyageuse interstellaire qui nous a donné un aperçu de ce à quoi ressemblent les comètes des autres systèmes solaires. L'astéroïde 514107, également connu sous le nom de Kaʻepaokaʻāwela, a une orbite inversée inhabituelle autour du soleil, probablement parce qu'il a été capturé depuis un autre système stellaire. Plongeons dans leur monde inhabituel ! Animation créée par Sympa.
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FunTranscript
00:00The solar system is full of mysterious objects from everywhere.
00:05In October 2017, researchers from Hawaii discovered a strange object they called Umuamua,
00:12meaning a visitor from a distant land, in Hawaiian.
00:16Or it's the burrowing of a very big cow.
00:19It followed an escape orbit, literally escaping the gravitational attraction of its planet,
00:24as if it was thrown a ball into space without any hope of return.
00:28This means that this unusual object comes from the outside of our solar system.
00:33The theories about it were numerous, from a simple asteroid to an alien spaceship.
00:40Some scientists have even considered that it is a piece of nitrogen ice,
00:45coming from a planet similar to Pluto.
00:47Its unusual shape only adds to the mystery.
00:50The significant variations of its luminous curve
00:53suggest that this object could be either elongated, like a tube,
00:57or flat, like a pancake.
00:59This object was unique in its kind.
01:01Umuamua did not behave like a comet or an asteroid.
01:05Comets, composed of ice, develop shiny tails as they approach the sun,
01:10while asteroids, mainly made of rocks, have no tails.
01:15Umuamua has no tail and does not release gas, but it is not a simple rock either.
01:20Its surface is very shiny, almost like polished metal.
01:23When it passed near the sun, its speed suddenly increased,
01:27as if it had been propelled by a rocket.
01:29And it was not the gravity of the sun that caused this sudden acceleration.
01:33Scientists do not know what caused it.
01:36So, what was this object really?
01:39After years of study, scientists now estimate that Umuamua
01:43is probably a comet covered with frozen hydrogen.
01:46This hydrogen reacted with the light of the sun,
01:49accelerating the comet and changing its trajectory.
01:52Umuamua probably accumulated this hydrogen
01:55by being exposed for a long time to cosmic rays.
01:58It also acquired a nice red tint thanks to this exposure.
02:02This object was a visitor from a young chaotic solar system,
02:06where collisions and migrations are frequent.
02:09Such systems often propel many small objects.
02:13It is possible that it was ejected by a planet such as Jupiter,
02:17whose gravity is so intense that it can project huge objects through space.
02:22This phenomenon also occurs with the comets we observe.
02:26Umuamua has already left our solar system,
02:29although similar objects visit us from time to time,
02:32about once a year.
02:34To learn more about these mysterious visitors,
02:37astronomers plan to send a probe in pursuit of Umuamua.
02:40We will use the orbits of Earth and Jupiter
02:43to accelerate it enough to catch up with it.
02:46However, some visitors have stayed a little longer in our neighborhood.
02:50In October 2019, the Hubble Space Telescope
02:53captured the image of a bluish comet,
02:56surrounded by dust and gas.
02:58At that time, it was already in our solar system,
03:01about 420 million kilometers from Earth,
03:04somewhere between Mars and Jupiter.
03:07We were able to observe the luminous dust surrounding it,
03:10but its core was still invisible due to its small size.
03:13However, small and relative here,
03:16this comet is about 1,000 meters wide,
03:19the length of 10 football fields.
03:21In March 2020, Hubble images revealed
03:24that a small fragment had detached from the core,
03:27indicating that this comet is very active, unlike Umuamua.
03:30By examining the object more closely,
03:33we discovered that its core was a mixture of ice and dust particles.
03:37Its surface is also similar to that of other comets,
03:40with rough areas and smooth layers of icy and dusty debris.
03:44This comet was discovered by the amateur astronomer
03:47Gennady Vladimirovich Borisov,
03:49and was therefore nicknamed Comet 2i Borisov.
03:52Scientists have quickly confirmed
03:54that it came from outside our solar system.
03:57This comet was like a tourist enthusiast.
04:00It was moving at a dizzying speed of about 180,000 km per hour.
04:04Such a speed would allow to go around the Earth 4 times in an hour.
04:09But this visit was fascinating for many other reasons.
04:13Most of the comets in our solar system
04:16come from the Quipper Belt or the Oort Cloud.
04:19The Quipper Belt is a region of space beyond the orbit of Neptune,
04:23similar to a large distant ring around the Sun,
04:26and filled with many icy objects.
04:29They are all ancient remains of the time
04:31when our solar system was still very young.
04:34The Oort Cloud is much further away.
04:37It forms a gigantic bubble around the solar system,
04:40also filled with very ancient icy objects.
04:43Most long-term comets come from there.
04:46But where does Comet 2i Borisov come from?
04:49We still do not know for sure.
04:52Scientists estimate that it could have been formed in another stellar system,
04:56which could be either younger or older than ours.
05:00NASA had accustomed us to more precision.
05:03In any case, it is possible that it was expelled from its original system,
05:07just like the summer or the month of May.
05:11Although Comet 2i Borisov is too small to maintain its own
05:15to maintain its own
05:17to develop a hair when it approaches the Sun.
05:20The term hair
05:22refers to this magnificent cloud of luminous gas and dust
05:25that surrounds the core of the comet.
05:28It is formed when the heat of the Sun causes the vaporization of the ice that is there.
05:32Thus releasing dust and gas into space.
05:35This comet was more friendly than Oumuamua
05:38and allowed us to study it more.
05:41We have thus discovered interesting characteristics,
05:44such as the fact that it had never interacted with another star, for example.
05:47Unfortunately, Borisov also had to leave us.
05:50It is now on a path that will take it back to interstellar space.
05:54Nevertheless, other visitors are approaching us.
05:57And you may have heard of this one.
06:02The Great Comet of 1996.
06:05This is how we nicknamed the Hyakutake Comet.
06:08It was also named after the astronomer Yuji Hyakutake
06:12who discovered it, by an incredible coincidence,
06:15on the eve of the New Year.
06:17On March 25, 1996,
06:19this object passed incredibly close to Earth.
06:22Barely 0.1 astronomical unit,
06:25a little further than the Moon.
06:27It flew over the North Pole,
06:29making this interview one of the closest
06:31with a comet of the last 200 years.
06:34Visible all over the world,
06:36it was very bright and spread widely in the sky.
06:39And it did not stop being visible for a single night.
06:42It became more and more apparent during the month of March,
06:46ranking among the brightest objects in the night sky at the end of the month.
06:50It completely disappeared at the end of May.
06:53It is a long-term comet,
06:55which means it takes hundreds of years
06:57to orbit around the Sun.
06:59The last time it visited us
07:01was about 17,000 years ago,
07:03but its orbital period has now increased
07:05to 70,000 years.
07:07But do not worry,
07:09other comets will illuminate our days and nights.
07:11In addition, some space objects
07:13prefer to take longer.
07:16Then comes this asteroid,
07:18Ka-Hepaoka Auella.
07:20You will excuse me if I misspell the name.
07:22In Hawaiian,
07:24it means Jupiter's mirror.
07:26Fortunately, the scientists
07:28had the kindness of naming it BZ
07:30to facilitate the life of your friendly narrator.
07:33It is a small asteroid,
07:35about 2.9 km in diameter.
07:37As its name suggests,
07:39it shares an orbit with Jupiter.
07:41But here is a fascinating detail.
07:43This asteroid moves in the opposite direction,
07:46what is called a retrograde orbit.
07:49This unusual asteroid
07:51was discovered in November 2014.
07:53It orbits around the Sun
07:55for about 11 years and 8 months,
07:57sometimes going inside
07:59and outside the orbit of Jupiter.
08:01It has been like this for at least 1 million years,
08:04and it will continue like this
08:06for another million years.
08:08But why does it move so uniquely?
08:10BZ could well be
08:12an interstellar vagabond.
08:14Maybe it passed through our solar system
08:16about 4.5 billion years ago,
08:18when the Sun was formed.
08:20Then, it would have been captured
08:22by its gravity,
08:24keeping an opposite orbit.
08:26Or maybe it comes from the cloud of Oort.
08:28In this case,
08:30it could have inherited its strange orbit
08:32of the mysterious new planet.
08:34A hypothetical body,
08:36whose existence is suspected
08:38in our solar system,
08:40far beyond Neptune.
08:42Whatever it is,
08:44this asteroid offers us
08:46a precious insight into the history
08:48of the solar system
08:50and the way in which organic matter
08:52comes from distant space.
08:54They stay there for variable periods of time.
08:56But sometimes, we are lucky,
08:58and they teach us a lot
09:00about the space around us.