Le saviez-vous, notre système solaire aurait pu avoir une planète supplémentaire ? Les scientifiques croient qu'une mystérieuse neuvième planète a pu exister autrefois mais a été expulsée il y a bien longtemps ! Cette planète "perdue" aurait pu être projetée dans l'espace profond durant les premiers jours chaotiques de notre système solaire, lorsque les planètes massives étaient encore en mouvement. Jupiter ou Saturne pourraient avoir utilisé leur forte gravité pour la propulser loin, la laissant dériver dans l'inconnu. Si cette planète est toujours là-bas, elle pourrait errer quelque part bien au-delà de notre portée. Alors, notre système solaire était-il censé avoir une planète de plus ? On dirait bien que l'univers en a décidé autrement ! Animation créée par Sympa.
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FunTranscript
00:00Let's see, there is Mercury, Venus, Earth, Mars, Phaethon, Jupiter.
00:11Wait, what? Phaethon? But what is that?
00:16At the beginning of the 19th century, the asteroid belt had not yet been discovered.
00:22In 1801, a man named Giuseppe Piazzi spotted the largest asteroid in the solar system, Ceres.
00:30At that time, people believed that there was a planet in orbit between Mars and Jupiter, and Ceres seemed to correspond to this description.
00:38But the following year, another astronomer, Heinrich Olbers, found another celestial body following a similar orbit.
00:46It was an asteroid later named Pallas.
00:49This discovery helped Olbers to understand that these two space objects could be the fragments of a planet.
00:55The discovery of two other asteroids, Vesta and Juno, seemed to confirm this theory.
01:01It was thought that this planet, which was named Phaethon in the 20th century, had appeared shortly after the formation of the solar system and had then been destroyed.
01:11These debris would have made up the asteroid belt. Olbers' idea received the name of the theory of perturbation.
01:18For the astronomers of the time, it seemed obvious that the planet had one day hit a large space object, which had led to its disappearance.
01:26The most likely candidate was Nemesis, a hypothetical red or brown dwarf in orbit around our sun.
01:34According to another theory, Phaethon would have suffered an internal cataclysm that would have disintegrated it.
01:40Another idea, Phaethon would have been a little too close to Jupiter and would have been torn apart by the immense gravity of the gas giant.
01:48Today, however, astronomers no longer believe in Olbers' theory. A new idea replaced it.
01:55It was known as the theory of accretion. It claims that the asteroid belt is all that remains of the protoplanetary disk.
02:03This disk would have initially orbited around the sun, even before the formation of the planets.
02:09Unfortunately, due to Jupiter's gravitational forces, it never managed to transform into a planet.
02:16But what is this asteroid belt that we keep talking about? This region is located between the orbits of Jupiter and Mars.
02:23There are tons of asteroids and even minor planets.
02:27Some of them can sometimes migrate or be projected out of the asteroid belt towards the external solar system.
02:34The four largest asteroids in this area are Ceres, Vesta, Pallas and Igi.
02:39They represent half the mass of the entire belt.
02:43As for the rest of the mass, it is made up of innumerable smaller bodies.
02:49In many science fiction films about space, the main character enters an asteroid belt
02:56and has to make great efforts to slalom between the countless rocks that threaten to destroy his spaceship.
03:03Well, know that this has nothing to do with reality.
03:06Even if there are thousands of asteroids in this region, they are so spaced out that the risk of collision is almost zero.
03:12But hey, it's cinema after all.
03:14Anyway, when the asteroid belt formed, some objects began to gather and form what we call protoplanets.
03:23But the gravitational attraction caused by the formation of Jupiter made these collisions too violent.
03:30And instead of forming large spaceships, like planets, the asteroids ended up breaking up.
03:36Astronomers think that due to these collisions, more than 99.99% of the initial mass of the asteroid belt
03:43has been lost over the first 100 million years of the history of the solar system.
03:50Only the largest asteroids have enough gravity to have a spherical shape.
03:55The smallest are often just piles of debris, roughly solidified by gravity.
04:00And the smallest objects of the asteroid belt look like dust.
04:04As small as they are, all these objects, giant and tiny, revolve around the Sun.
04:10There are several types of asteroids, whose composition and albedo,
04:14the proportion of light or radiation reflected by a surface, vary.
04:18The main types are carbon asteroids, which have a very dark surface.
04:23The silicon asteroids, which can also be called stone asteroids, and the metallic asteroids.
04:30The first two types represent about 75% and 17% of the known asteroids.
04:36For the first time, the asteroid belt was crossed by a spacecraft in 1972.
04:42It was the Pioneer 10 probe.
04:45This machine made it possible to refute the theory that the belt was filled with dust
04:50and that it was capable of seriously damaging all the material on board.
04:53This did not happen, and since then, eight other probes have crossed the asteroid belt.
04:59And now, I'm going to tell you some interesting facts about the solar system itself.
05:04Try to count how many of these facts you already knew and write your answer in the comments below.
05:10The solar system is 4.5 billion years old.
05:15Scientists came to this conclusion after studying meteorites,
05:20the oldest material they managed to find.
05:24But our solar system is not the only one of the Milky Way.
05:27The galaxy in which we live is home to about 100 billion.
05:30All this for a single galaxy.
05:32So how many are there in the whole universe?
05:36Our sun also has an incredible mass.
05:38Here is the proof.
05:4099.86% of the mass of the solar system is made up of the mass of the sun,
05:45in particular by the hydrogen and helium that make it up.
05:49The remaining 0.14% mainly corresponds to the mass of the eight planets in the system.
05:55In fact, contrary to popular belief, space is not a perfect vacuum.
06:01It contains not only stars and planets, but also interstellar dust clouds,
06:07space plasma and cosmic rays,
06:10fragments of atoms that come from the borders of the solar system.
06:15A phenomenon that astronauts should be concerned about when they explore space and cold welding.
06:20If two pieces of the same type of metal touch each other in space,
06:24they bind and remain permanently glued,
06:27a bit like with galaxy glue.
06:30This does not happen on Earth because water and air keep things apart.
06:35You can see solar eclipses, because even if the moon is 400 times smaller than the sun,
06:41it is also 400 times closer to Earth.
06:44It is therefore perfectly capable of obscuring our star.
06:47But in 600 million years, the moon will no longer be able to completely block the sun
06:52due to the evolution of the orbit of the satellite.
06:56Behind the orbit of Neptune is the mysterious belt of Kuiper,
07:00filled with immense ice objects.
07:03The most curious thing about this space formation
07:06is that scientists are unable to explain the pattern of its movement.
07:11The only explanation they have is that Neptune could hide a gigantic planet.
07:17This hypothetical planet has already received the name of Planet 9.
07:21And all we have to do is wait for its existence to be confirmed.
07:25Or not.
07:27Jupiter's ocean is larger than all the water areas of the other planets in the solar system.
07:32But it is very different from terrestrial oceans.
07:35In fact, it is not made up of water.
07:38This fascinating expanse is actually made up of metallic hydrogen,
07:42and its depth is about 4000 km,
07:45which is about the circumference of the Earth.
07:49People discovered the magnificent rings of Saturn in the 1600s.
07:54But we now know that Saturn is not the only planet with rings.
07:59All the giant gas planets, Uranus, Neptune and Jupiter,
08:04have their own rings.
08:06But they are thin and almost impossible to see.
08:09As for Mars, Venus and Earth,
08:11they are made up of rocky materials and have no rings.
08:15At the same time, the moon of Saturn, Rhea,
08:17could have a ring system made up of three narrow bands.
08:21If astronomers can confirm it,
08:23it will be the first time that rings around a moon will be discovered.
08:27And Mars could also get rings in the 70 million years to come.
08:32Its largest moon, Phobos, is getting closer and closer to it.
08:36One day, due to the gravitational attraction of the red planet,
08:40this satellite is likely to break and turn into a ring.
08:44It could then last for millions of years.
08:47Another interesting fact about Mars,
08:50you have probably heard of methane,
08:53a by-product of natural processes such as volcanic activity and bovine flatulences.
08:58Anyway, this gas is not only part of the Martian atmosphere,
09:02but it is also the source of many confusions for astronomers.
09:06Indeed, the volume of methane on Mars fluctuates constantly.
09:10And scientists can't determine where it could come from.
09:14Could there be life on Mars?
09:16Could there be cows?