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?
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