Hé, amateurs de l'espace ! Prêts à embarquer pour un voyage hors de ce monde ? Nous avons quelque chose de spécial pour vous - une vidéo remplie de faits spatiaux stupéfiants qui vous laisseront étoilé et en quête de plus de connaissances cosmiques. Des mystérieux trous noirs à l'échelle impressionnante de l'univers, cette vidéo a tout. Que vous soyez un observateur d'étoiles aguerri ou que vous trempiez simplement vos orteils dans le cosmos, il y a ici quelque chose pour éveiller votre curiosité et élargir vos horizons cosmiques. Cliquez sur play maintenant, et découvrons ensemble les secrets de l'univers. ✨ Animation créée par Sympa.
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Musique par Epidemic Sound https://www.epidemicsound.com
Pour ne rien perdre de Sympa, abonnez-vous!: https://goo.gl/6E4Xna
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Nos réseaux sociaux :
Facebook: https://www.facebook.com/sympasympacom/
Instagram: https://www.instagram.com/sympa.officiel/
Stock de fichiers (photos, vidéos et autres):
https://www.depositphotos.com
https://www.shutterstock.com
https://www.eastnews.ru
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Si tu en veux encore plus, fais un tour ici:
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FunTranscript
00:00 Our solar system is a rather strange place, with all its unusual phenomena,
00:06 that we have not yet managed to explain.
00:09 According to some, a gigantic undiscovered planet would hide behind Neptune,
00:15 volcanoes on Pluto would spit out ice,
00:18 and on Mars, a huge canyon could contain the entire territory of the United States.
00:24 So let's go back to the most mysterious facts of the solar system.
00:28 It is 4.6 billion years old.
00:31 It is so old that we speak of a superior solar system.
00:34 This is what scientists have concluded after studying the oldest materials they have found,
00:40 and by that I mean meteorites.
00:43 Venus is a planet where you can't wear a hat.
00:47 Violent winds blow there 50 times faster than the rotation of the planet.
00:52 They never stop, and they even seem to strengthen over time.
00:57 Do you want to change the air?
00:59 You have to move 17.7 billion kilometers away from the Earth to leave the solar system.
01:06 Don't forget your GPS.
01:08 You've probably heard of methane,
01:11 a gas from natural processes such as volcanic activity.
01:16 This gas is not only part of the Martian atmosphere,
01:20 but it is also the cause of the greatest confusion among astronomers.
01:24 Indeed, the volume of methane on Mars never stops growing,
01:29 and scientists can't understand where it comes from.
01:33 Is there life on Mars?
01:36 As you may remember, Pluto was once considered a planet,
01:40 but it lost this title in 2006.
01:43 Later, it was re-classified as a dwarf planet,
01:46 but the most surprising thing is its size,
01:49 which is smaller than that of the United States.
01:52 From east to west, the United States is about 4,344 kilometers,
01:57 and the diameter of Pluto is only 2,370 kilometers.
02:02 Uranus rotates on one side,
02:05 and astronomers have no idea why this planet decided to do that.
02:11 It could possibly be due to ancient powerful asteroid collisions.
02:16 But that's just a theory.
02:18 Besides, Uranus is the only planet to rotate sideways.
02:22 Our Sun is incredibly massive.
02:25 99.86% of the entire mass of the Solar System
02:29 is the mass of the Sun,
02:31 mainly because of the hydrogen and helium it is made of.
02:36 The remaining 0.14%
02:38 represents mainly the mass of the eight planets of the Solar System.
02:43 Earth is not the only planet in the system to have a tectonic activity.
02:48 Astronomers have found what looks like cliffs on Mercury.
02:53 The tectonic activity could indeed explain its rapid shrinkage.
02:59 In science fiction movies,
03:01 the hero often finds himself in an asteroid belt
03:04 where he is quickly overwhelmed by flying rocks.
03:07 Well, sorry to disappoint you,
03:09 but it has nothing to do with reality.
03:12 The only asteroid belt that astronomers know of
03:15 is located between Mars and Jupiter.
03:18 There are thousands of asteroids in this area,
03:21 but they are so spaced out that the risk of collision is almost zero.
03:25 Behind Neptune's orbit
03:27 is the mysterious belt of Kuiper,
03:30 filled with massive ice cores.
03:33 The most curious thing about this formation
03:36 is that scientists can't explain its movement.
03:39 Their only explanation is that Neptune could hide the view of a gigantic planet.
03:45 This hypothetical planet has already been nicknamed "Planet 9"
03:50 and we just wait for its existence to be confirmed.
03:53 Or not.
03:55 Volcanoes on Earth are as different from those of Pluto
03:58 as fire and ice.
04:00 Literally.
04:02 While our volcanoes spit lava,
04:05 Pluto's volcanoes spit ice.
04:08 When it is frozen, the water expands
04:11 and this enormous pressure accumulates until, boom,
04:14 the ice creates an eruption.
04:17 This is called a cryovolcano.
04:20 Jupiter, one of Saturn's moons,
04:23 has a unique color.
04:25 It is bicolor.
04:27 One of its hemispheres is light,
04:29 and the other is sinisterly dark.
04:31 Scientists have not yet clarified this mystery.
04:34 There is something else strange about Pluto's atmosphere.
04:37 First of all, it rises much higher above the planet's surface
04:41 than our Earth's.
04:43 And on top of that, it has more than 20 layers of super-cold, condensed strands.
04:48 We live inside the Sun.
04:51 No, I don't mean that we are the inhabitants of this reddish light ball
04:55 located about 150 million kilometers away.
04:58 But the atmosphere of the Sun extends well beyond its visible surface.
05:02 And our planet is inside.
05:05 It is the solar wind gusts that create the stunning phenomenon
05:09 of the auroras of Boreal and Austral.
05:12 The ocean on Jupiter is larger than those of all the other planets in the solar system.
05:17 But it is not the kind of ocean you think of, because it is not made of water.
05:21 It is a deep ocean of metallic hydrogen,
05:24 40,000 kilometers deep,
05:26 which is the equivalent of the circumference of the Earth.
05:29 The atmosphere of the Sun is warmer than the surface of the star.
05:33 While on the surface, the temperatures reach 5,000 degrees Celsius.
05:38 Its high atmosphere is almost 100 times warmer.
05:41 Scientists suspect that the heat explosions from the Sun
05:45 could have a link with this unique phenomenon.
05:48 We learned about the existence of the magnificent rings of Saturn in the 1600s.
05:53 But it is only recently that it became obvious
05:56 that Saturn was not the only planet to have rings.
05:59 All the gas planets of Uranus, Neptune and Jupiter also have rings,
06:04 but they are extremely thin and almost impossible to distinguish.
06:07 As for Mars, Venus and Earth,
06:10 they are made up of rocky materials and have no rings.
06:14 Our system is not the only one in the Milky Way galaxy.
06:17 The galaxy in which we live is home to about 100 billion.
06:21 So imagine the whole universe.
06:24 On Earth, you can at any time fall on rocks from Mars.
06:28 After analyzing the chemical compounds of some meteorites
06:32 found in the Sahara Desert, as well as in Antarctica and other places on our planet,
06:38 scientists came to a shocking conclusion.
06:41 In our solar system, most planets rotate in the opposite direction of the needles of a watch.
06:47 Most, but not Venus.
06:49 This rebel planet has decided to go in the classical direction,
06:52 and scientists are still trying to understand why.
06:55 Besides, why do planets rotate?
06:58 What defines their rotational speed?
07:00 And does the sun rotate too?
07:02 Fasten your seatbelt and let's try to answer these questions.
07:05 Venus is the second planet from the sun and the warmest of our solar system.
07:11 Did you know that Venus is sometimes called the twin of the Earth?
07:15 Indeed, its size and composition are similar to that of our planet.
07:19 But the similarities stop there, because Venus is a rather disjointed place,
07:23 that's the least we can say.
07:25 For example, let's take the climate.
07:27 On Venus, it's always hot and there are clouds.
07:30 And when I say hot, I'm not exaggerating.
07:32 It's over 436 degrees.
07:35 And these clouds?
07:36 They are not made of water like on Earth.
07:38 They are made of sulfuric acid.
07:40 So, indeed, on Venus, it's better not to go out without an excellent sunscreen.
07:45 If we look at the photos taken from its surface,
07:48 we can see clouds, a toxic yellow and cracked and desolate landscapes.
07:53 It should be noted that the spacecraft that took these photos
07:56 went out almost immediately after having sent them.
07:59 Poor little one.
08:01 But the surface of Venus is not just a solid, dark and flat Earth.
08:05 In fact, Venus has mountains higher than Mount Everest.
08:10 But they are not made of rocks like those on Earth.
08:13 They are made of a more dense volcanic material than rock.
08:17 Venus is a rather frightening place that contains many mysteries.
08:23 One of them has intrigued scientists for years.
08:26 It is therefore the rotation of the planet.
08:28 Most of the planets in our solar system rotate in the opposite direction of a watch.
08:33 But Venus is not like the others.
08:35 It rotates in the right direction.
08:37 And that's not all.
08:38 It also rotates around the sun faster than on itself.
08:43 In other words, on this planet, a year goes by faster than a day.
08:47 It's a bit like Venus had chosen eccentricity as a life mission.
08:51 But why?
08:52 Scientists have some theories.
08:55 According to the most widespread idea,
08:57 before, Venus was rotating in the opposite direction of the clocks of a watch, like the others.
09:01 But something happened that changed his mind.
09:04 And what is it, you will tell me?
09:06 An object the size of a planet.
09:09 Astronomers think that something huge has collided with Venus,
09:13 sending it upside down in the opposite direction.
09:16 We can imagine it as a cosmic billiard ball.
09:20 The huge mysterious object being the billiard ball and Venus, the target ball.
09:25 But we can't say that Venus goes in the wrong direction.
09:30 There is no wrong direction of rotation in the universe.
09:34 This is called retrograde rotation.
09:37 It's the case when a planet rotates in the opposite direction of its orbit around the sun.
09:42 Venus, for example, has a retrograde rotation.
09:46 Which means that the sun rises in the west and sets in the east on this planet.
09:51 Now, when your horoscope tells you "Mercury retrograde", you'll know what it's about.
09:57 But Venus is not the only strange planet in our solar system.
10:01 There are quite crazy planet rotations.
10:05 For example, most of the planets in our solar system rotate around an imaginary line called an axis.
10:12 This axis is generally rectilinear in relation to the orbit of the planet around the sun.
10:18 However, some planets like Uranus have an inclined axis,
10:23 which means that it is almost on the side in relation to its orbit.
10:27 This inclination means that the poles of the planet are almost on the same plane as their orbit.
10:32 As the planet rotates around the sun, different parts receive different amounts of sunlight.
10:40 This leads to extreme seasonal variations.
10:43 For example, one pole can be permanently exposed to sunlight,
10:47 while the other will be plunged into total darkness for a long time.
10:51 Uranus is the only planet in our solar system to rotate on itself.
10:56 Scientists think it could have reproduced the history of Venus.
11:01 It was a time when a major impact made Uranus tilt out of its original rotation axis,
11:07 making it take a 98-degree angle.
11:11 We should be grateful to Jupiter.
11:14 Its crazy gravity attracts all asteroids and protects us from such collisions.
11:19 All this is somewhat similar to what we call "synchronized rotating planets by tidal effect".
11:25 Yes, it's a bit long.
11:26 Let's imagine that you are on a date with a planet, but instead of being charming and mysterious as you would expect,
11:31 it is content to stare at you with the same face all night.
11:34 This is basically what happens with these planets.
11:38 They rotate around their axis at the same speed as they rotate around their star.
11:45 This means that the same side of the planet is always facing the star,
11:49 while the other side is constantly in the dark.
11:53 This phenomenon can have strange effects on the climate and weather conditions of the planet.
11:58 The side facing the star can become extremely hot, while the other can be incredibly cold.
12:05 The atmosphere of the planet can also become very unstable,
12:08 with violent winds blowing from the hot side to the cold side.
12:12 And it's not just the planets that are affected.
12:14 Our Moon also works this way.
12:17 Did you know that we only see one side of the Moon?
12:21 It's because it is locked by the Earth.
12:25 We can also take the example of the dwarf planet Pluto.
12:29 What would happen to us and our planet if it became as big as the Sun?
12:35 The diameter of the Earth is 12,874 km.
12:39 Crossing it is like going back and forth three times across the United States.
12:43 It doesn't seem like a lot, does it?
12:45 Well, what would you say if you repeated this trip 305 times?
12:49 Imagine the fuel costs.
12:52 It's the diameter of the Sun, about 1,392,082 km.
12:58 Compared to our Earth, the Sun is of an unimaginable size.
13:02 So what would happen to us if we caught up with it?
13:06 There are four possible scenarios, depending on what we mean by "the size of the Sun".
13:12 First scenario.
13:17 The Earth becomes as big as the Sun, but its mass remains the same.
13:23 A gigantic planet with the mass of a very small Earth.
13:27 First of all, goodbye to gravity.
13:31 The bigger the planet, the stronger its gravity, and vice versa.
13:35 Such a light planet would simply not be able to attract anything to it.
13:41 Gravity creates all heavy substances.
13:44 Everything, from rocks to entire continents, is maintained thanks to it.
13:49 I think you guessed what would happen without it.
13:54 We would all turn into dust particles.
13:57 Yes, the Earth would simply become a cloud of dust.
14:00 Oh, and to complicate things, the gravities of the other planets would stretch us aside,
14:05 leaving no chance for our planet to regain its original form.
14:09 This scenario is not the best, don't you think?
14:13 Besides, even if the Earth remained a planet, life could not be born there in these conditions.
14:20 There would be a considerable distance between the center of the Earth and its surface.
14:24 And remember, the mass of the planet is tiny, so no gravity.
14:29 It would not have been able to retain the atmosphere,
14:32 and without atmosphere, living organisms could not develop.
14:37 It wouldn't have mattered anyway.
14:39 The Earth would actually be a cloud.
14:42 And so, this cloud, weighing about ten times more than Jupiter, would concentrate in space.
14:48 As a result, it would burst and turn into a star.
14:52 And we would have a new sun.
14:55 Scenario 2
14:57 This is both a one-off scenario, but also a consequence of the previous one.
15:02 The Earth becomes as large as the sun and has the same mass.
15:07 Now we have two suns.
15:09 We would be a so-called binary stellar system.
15:12 This would mean the destruction of our solar system.
15:17 Imagine having two masses in a single system.
15:21 The orbits of the planets would become unstable, disturbed by such a sudden change.
15:26 Once they would get closer to our exo-Earth, they would collapse immediately,
15:30 either because of the forces of the tides, or because of the impact of the exo-Earth.
15:34 Yes, even the gas giants. I mean you, Jupiter.
15:39 Do you know which planet would survive and finally take its revenge on us?
15:43 Pluto.
15:44 It would probably be the last remaining exoplanet in the whole system.
15:48 It is too far away to notice changes.
15:51 Except in case of mass increase in the center of the system.
15:55 So Pluto's orbit would get closer to our two-star system.
15:59 And that's all.
16:01 The Earth and the Sun should accept that Pluto is now their only planet.
16:06 The proto-planetary disk that formed our system billions of years ago would no longer exist.
16:12 So no other planet could be created in our system.
16:16 All this is beautiful, but what about the Earth itself?
16:20 What would life look like?
16:22 Let's see.
16:24 The nights and the days would now last longer,
16:27 because of the increase in the Earth's rotation time.
16:30 There would probably be a significant decrease in temperature in the North and South Poles.
16:34 Even on our little planet, they only receive very little sunlight.
16:38 So if the Earth's size increased,
16:40 the area of the poles that would receive sunlight would decrease even more.
16:45 The positive side is that there would be a lot more space now.
16:49 There would be no more overpopulation.
16:51 The size of the planet would be so huge that it would take years to go from one point to another.
16:57 Yes, when you think about it, you would probably feel very lonely.
17:01 But who knows?
17:03 Maybe rockets would become our main means of transport.
17:06 That would be great!
17:08 There would be many vast and unexplored regions that no human would have ever seen or visited.
17:13 We would not know either the existence of many different civilizations and tribes.
17:18 The centuries would pass,
17:20 and many of us would go without ever meeting other people and learning to know them.
17:25 And yet, if we were to walk,
17:29 our bones would not be able to bear our weight with such a considerable gravity.
17:33 And our heart would have to work twice as hard to keep us alive.
17:37 Birds would not be able to fly anymore.
17:40 Nothing could fly, a priori.
17:42 All the existing trees would fall.
17:44 And the new ones would barely grow back.
17:47 Like grass.
17:49 Speaking of trees, how would our ecosystem behave?
17:53 Well, not very well.
17:55 If we do not take care of our environment in our little land right now,
17:59 imagine what would happen if we had such a vast space at our disposal.
18:03 I suppose that our tons of waste would even have been worth the infinite reserves of trees
18:07 and drinking water that we would have in our big new house.
18:11 Our machines and robots would have to be huge to be effective.
18:19 That is because an ordinary farm would now be the size of an American state.
18:24 It would also be much darker than what we are used to.
18:28 The Earth is so small now.
18:31 Imagine what would happen if our planet were the size of the sun itself.
18:35 Less sunlight means that we would probably need artificial sun.
18:40 In addition, the temperature differences on the surface of the planet would be huge.
18:45 If you are surprised, it is because you probably underestimated the size of the sun.
18:49 It is almost 110 times larger than the Earth.
18:53 The equator of our new Earth is equal to the 35 equators of our current Earth.
18:58 In space, no one can hear you scream.
19:03 As everyone knows, star explosions, asteroids crashing and planets on fire
19:08 do not make any noise in space.
19:11 Really.
19:13 What if we could hear some noise up there?
19:16 OK, back to school.
19:18 Sound is a mechanical wave coming from a vibration.
19:21 But what does that mean exactly?
19:24 The most famous example is that of guitar strings.
19:27 If you scratch one of them, it starts to vibrate.
19:29 The atoms inside the metal string begin to shake and hit the atoms of the air around them.
19:35 The atoms push each other until some reach our ears.
19:39 It's like the wave created by a stone thrown into a pond.
19:42 And it happens very quickly, at a speed of about 340 m/s.
19:47 Then our eardrums begin to vibrate at the same frequency.
19:52 And the small holes inside our ears transmit this vibration to the brain.
19:56 The brain then uses its magic, recognizes the pattern and transforms it into sound.
20:02 Great.
20:04 Now we know that we need certain particles to create sound.
20:08 And we can find these particles in gases, liquids and solid substances.
20:13 But what about space?
20:15 It's an almost perfect vacuum.
20:17 And you've probably heard that there is no sound in space because it's a vacuum.
20:22 But what does that really mean?
20:25 A perfect vacuum is a totally devoid of matter.
20:29 That means there is nothing in this place.
20:32 Yes, despite all these celestial bodies in space,
20:35 there is no air between them, no atoms or particles.
20:39 Nothing at all.
20:41 In fact, almost nothing.
20:43 To be exact, the perfect vacuum doesn't really exist.
20:46 We can't get rid of atoms, but space is very close to this notion.
20:51 On average, there are 1 to 5 atoms per cubic centimeter.
20:55 It may seem like a lot, but you have to keep in mind that these atoms are microscopic.
21:00 And the distance between them is huge.
21:03 For comparison, 1 cubic centimeter of air contains about 1000 atoms.
21:08 So, of course, with such a low density, these atoms can't push each other.
21:13 Even if the vibration is very strong, as in the case of a supernova, for example.
21:18 They still can't do it.
21:21 But then, movies are lying to us.
21:23 All these epic space scenes actually take place in an almost embarrassing silence.
21:29 Not so fast.
21:31 What if we told you that there are, in fact, certain ways to hear the sound in space?
21:36 First of all, there is always noise on other planets.
21:40 If there is an atmosphere on a space body, or at least something like gas, water or a solid surface, there will be noise.
21:48 In our case, the atmosphere becomes completely silent about 100 km above the surface of the Earth.
21:55 This is where the sky stops being blue and a black starry veil begins.
22:00 In any case, you would have to land on another planet or at least get close to its atmosphere to hear something.
22:07 But whatever it is, the sound would be very different.
22:11 Let's take the example of our sister planet, Venus.
22:14 The atmosphere there is very dense.
22:16 Scientists even qualify it as a "thick chemical soup".
22:21 If you managed to stay alive and talk there, your voice would be very different.
22:27 It would be much louder and deeper.
22:31 So, if you've always wanted to sing like Pavarotti, now you know what to do.
22:36 And what would happen if the Earth had a denser atmosphere?
22:40 What would we hear?
22:42 Well, you can vaguely imagine it if you've ever been in the water.
22:47 The water is very dense. The sound moves much faster and better than in the air.
22:52 At a speed of almost 2 km per second.
22:57 If you sat in an empty room without a sound source, you wouldn't hear much, would you?
23:03 Now, dip your head in the water and observe how the same silence resonates here.
23:08 It's not silent at all.
23:10 Even if you ignore the omnipresent sounds of the water itself,
23:13 you will immediately notice how much you can hear your own body.
23:17 How your blood pulses in your veins, how your heart beats,
23:20 the slightest movement of your fingers.
23:22 Pretty scary, isn't it?
23:24 This gives us an idea of what would happen to us on a planet with a denser atmosphere.
23:29 And it's just crazy.
23:31 We would hear everything.
23:33 Animals running or the movement of tectonic plates.
23:38 So it's obvious that there is sound on other planets.
23:42 But what about space?
23:45 There is also sound, for example, in a cloud of dust.
23:49 You can find space dust almost everywhere in space.
23:52 It can be the remains of a star or something else.
23:55 And in these places, everything is a little denser than normal.
23:59 This means that there are probably dust clouds
24:03 where particles are very close to each other.
24:06 Which means they can produce sounds.
24:08 Of course, these will be very weak and transmitted over a very short distance.
24:12 But it's still better than nothing, isn't it?
24:16 It turns out that we have already recorded a spatial sound.
24:19 It comes from the galactic lava of Perseus,
24:22 which is 250 million light years away from us.
24:26 NASA recorded it in 2003.
24:30 It looks like a note in B flat.
24:34 But its frequency is so low that the human ear unfortunately cannot perceive it.
24:39 But apart from that, we can only hear something inside space ships.
24:44 After all, they are small air pockets.
24:47 In a space suit, you would also hear the sounds very well,
24:51 including your breathing or the circulation of your breast.
24:55 But two astronauts floating side by side would not hear each other,
24:59 even if they approached and shouted very loudly.
25:02 The Sun is a medium-sized star.
25:05 And yet it could contain 1,300,000 Earths.
25:09 The star is also 333,000 times heavier than our planet.
25:14 NASA has translated radio waves created by the atmosphere of the planets into audible sounds.
25:19 This is how astronomers have discovered that the sound produced by Neptune
25:23 resembles the waves of the ocean,
25:25 that Jupiter seems to be underwater,
25:28 and that Saturn's voice sounds like horror movie music.
25:32 And that the Earth, it, sounds a bit like jazz bebop.
25:35 Okay, I made that up.
25:38 The surface of the Sun is burning, but a lightning is five times hotter.
25:44 The Earth is struck by 100 lightnings every second,
25:48 which represents 8 million lightning strikes per day and about 3 billion per year.
25:53 Unbelievable!
25:55 If you ever manage to go to the Moon and see traces of recent steps,
25:59 that doesn't mean there's someone else with you.
26:02 Steps or other marks of the same type can last a million years there,
26:07 because the Moon has no atmosphere.
26:10 There is no wind, not even a small breeze that could even slowly erase these footprints.
26:15 Astronomers have found the biggest hole we've ever seen in the universe.
26:20 It's called the Giant Void, and it extends over a surface of a billion light years.
26:25 It was by accident that it was discovered.
26:27 One of the team members was a bit bored and wanted to see how things were going
26:32 in the direction of the cold point.
26:34 It's an anomaly in the cosmological diffuse background map, or FDC in abbreviated.
26:39 It's a faint glow that reaches our planet from different directions and fills the universe.
26:45 It has been crossing space for nearly 14 billion years
26:48 and is what remains of the light production that followed the Big Bang.
26:53 So, you fall in the middle of a black hole and prepare for a sad ending.
26:58 Don't panic.
27:00 Falling into a black hole won't necessarily destroy you, you or your spaceship.
27:05 You'd have to choose a large black hole to survive.
27:08 If you fall into a small black hole, what we call the event horizon is very narrow.
27:13 Gravity, on the other hand, increases a little more every centimeter.
27:17 So, if you extend your arm forward,
27:19 you'll have a big difference in gravity between your fingers and your elbow.
27:23 This will have the effect of stretching your hand,
27:25 causing a rather unpleasant sensation.
27:27 Very unpleasant, to be honest.
27:29 Things wouldn't be quite the same if you fell into a supermassive black hole
27:33 like the ones in the center of galaxies.
27:35 These objects can be millions of times heavier than the sun.
27:38 Their event horizon is vast, and gravity doesn't change that quickly.
27:42 So, the force you'd feel on your heels and at the top of your head would be about the same.
27:47 And you could go all the way to the heart of the black hole.
27:50 Well, that's still to be proven.
27:53 If you watch a very touching movie in space and start crying,
27:57 your tears won't flow.
27:59 They'll accumulate around your eyeballs.
28:02 Your eyes will become too dry, and you'll feel like they're burning.
28:06 All the liquid on your body will evaporate, including the surface of your tongue.
28:11 Speaking of burning, it's something fire can't do in space.
28:15 Indeed, fire can spread when there's an oxygen flow.
28:19 And since there isn't any in space...
28:22 Once they've exploded, stars aren't supposed to come back to life.
28:26 But some stars have somehow survived a huge supernova explosion.
28:31 These zombie stars are rather rare.
28:34 Scientists have found a very large one, called LP40365.
28:39 It's a partially burned white dwarf.
28:42 A white dwarf is a star that has burned all of its hydrogen.
28:46 And this hydrogen was once its nuclear fuel.
28:50 In this case, the final explosion was perhaps weaker than it usually is.
28:54 Not powerful enough to destroy the star as a whole.
28:58 It's as if a star wanted to explode but didn't succeed.
29:02 Which explains why some of the matter survived.
29:05 If you ever go into space, don't take off your suit.
29:08 Except if you're in a spaceship.
29:10 In space, the air in your lungs will spread,
29:13 as will the oxygen in the rest of your body.
29:16 You'll be like a balloon, twice as big as your normal size.
29:19 Good news, your skin is elastic enough to contain you.
29:23 Which means you won't explode.
29:25 A little comfort.
29:27 When an object enters a black hole, it changes shape and stretches like spaghetti.
29:32 This happens because gravitational force attracts an object in one direction,
29:37 while compressing it in another.
29:40 A sort of "leg paradox".
29:43 Besides, a black hole as big as an atom has the mass of a very big mountain.
29:49 There's one in the centre of the Milky Way, called Sagittarius A.
29:54 Its mass is equivalent to one billion suns.
29:57 But fortunately, it's very far from us.
30:01 If you made a big boom on an asteroid, you wouldn't be able to hear its noise.
30:07 Yes, we often hear the sound of spaceships and space battles in movies,
30:11 but it's just a myth.
30:13 Sound is a wave that spreads because of the molecules' vibrations.
30:17 A person hits a few metres away from you.
30:20 The sound wave starts pushing the first air molecule next to the explosion,
30:24 then the second, the third, and so on, until the wave reaches your ear.
30:29 To diffuse sound, we need molecules like air or water.
30:33 In the atmosphere, sound waves spread very well, but space is empty.
30:38 So there's nothing to hear.
30:40 You can hit your hand, but no molecule can vibrate and carry the sound.
30:46 So, to have a conversation, you need a radio or a good reading of lips.
30:53 Meteoroids are orbiting the Sun,
30:56 while most of the debris is in orbit around our planet.
31:01 For example, we've launched nearly 9,000 spacecraft into the world,
31:05 from satellites to rockets.
31:07 Even the smallest pieces can damage a spacecraft at such high speeds.
31:12 Galaxies, planets, comets, asteroids, stars,
31:16 space bodies are things we can actually see in space,
31:20 but they represent less than 5% of the total universe.
31:24 Black matter, one of the greatest mysteries of space,
31:27 is the name we use to designate the entire mass of the universe that is still invisible.
31:32 And there's a lot of it. It could even make up 25% of the universe.
31:36 Dark energy makes up 70% of the universe.
31:40 Hmm, that's 100%, right?
31:43 Venus was probably covered by an ocean 10 to 300 meters deep.
31:49 In addition, a certain amount of water was trapped in the planet's soil.
31:54 It had stable temperatures of 20 to 50 degrees Celsius,
31:59 which were therefore tolerable and not so different from the current temperatures on Earth.
32:04 In short, for 3 billion years,
32:07 until something unthinkable happened 700 million years ago,
32:11 Venus could have been habitable.
32:13 But today, it is no longer.
32:16 The moon is the second brightest object in our sky.
32:20 However, among the other astronomical bodies, it is one of the darkest and least reflective.
32:25 But our natural satellite seems bright because it is very close to us.
32:29 In the same way, our planet seems much brighter when you look at it from space.
32:34 It's because clouds, ice and snow reflect a lot more light than most rocks.
32:40 Triton, Neptune's moon, has its entire surface covered with several layers of ice.
32:45 If this satellite replaced our current moon,
32:48 the night sky would be 7 times brighter.
32:51 Neutron stars are among the smallest and most massive objects in space.
32:56 They are generally about 18 km in diameter,
32:59 but are several times heavier than the Sun.
33:02 And they rotate around 600 times per second,
33:05 much faster than a professional figure skater.
33:08 Saturn is the planet with the least density in the solar system.
33:12 It has a density equivalent to one eighth of that of the Earth.
33:15 And yet, because of its immense volume, the planet is 95 times more massive than the Earth.
33:21 The transitory lunar phenomenon is one of the most enigmatic things that happens on the Moon.
33:26 It is an ephemeral change of light, color or other, on the surface of the satellite.
33:31 Most often, it is random light flashes.
33:34 Astronomers have been observing this phenomenon since the 1950s.
33:38 They noticed that the flashes occurred in an unpredictable way.
33:42 Sometimes, they can occur several times a week.
33:45 Then, they disappear for several months.
33:47 Some of them do not last more than a few minutes, but some have lasted several hours.
33:52 In 1969, one day before Apollo 11 landed on the Moon,
33:57 one of the mission members noticed that part of the lunar surface was brighter than the surrounding landscape.
34:04 It was said that this area had a kind of fluorescence.
34:08 Unfortunately, we still do not know if this phenomenon was related to the mysterious lunar flash.
34:13 Waste is not only a problem in the oceans, cities and forests of the Earth.
34:18 There is what is called "spatial waste",
34:20 that is to say, any object made by man that has been left in space and is no longer useful.
34:25 There are also natural debris from meteorites and other cosmic objects.
34:30 There are currently more than 500,000 spatial debris orbiting the Earth,
34:34 at speeds high enough to cause significant damage if they collide with a space ship or a satellite.
34:41 NASA does its best to follow each object to ensure that missions out of Earth can reach their destination safely.
34:49 Our sun is incredibly massive.
34:51 For proof, 99.86% of the entire mass of the solar system consists of the mass of the sun.
34:58 In particular, the hydrogen and helium it is composed of.
35:01 The remaining 0.14% are mainly the mass of the eight planets of the solar system.
35:07 The atmosphere of the sun is warmer than its surface.
35:10 The temperature of the surface reaches 5,500 ° C, but the high atmosphere reaches millions of degrees.
35:17 If we could dig a tunnel directly in the center of the planet and go out on the opposite side,
35:23 and you were adventurous enough to jump in, it would take you 42 minutes to cross it.
35:29 You would accelerate as you fell to reach the maximum speed when you reached the core of the Earth.
35:35 After half the journey, you would then fall up more and more slowly.
35:40 When you reached the opposite surface, your speed would be back to zero.
35:44 Unless you manage to get out of the hole, you would immediately start falling again,
35:49 to go down or go up to the other side of the planet.
35:53 This journey would last an eternity, and this because of the bizarre effects of gravity.
35:58 There could be more metals, for example titanium or iron, in the lunar craters than astronomers thought.
36:08 The biggest problem with this discovery?
36:10 It contradicts the main theory about how the Moon was formed.
36:14 This theory states that the Earth's natural satellite detached itself from our planet after a collision with a massive space object.
36:22 But then, why does the Earth's crust, poor in metals, contain much less iron oxide than the Moon's?
36:28 This could mean that the Moon was formed from materials much deeper inside our planet.
36:34 Or these metals could have appeared when the lunar surface, in fusion, cooled slowly.
36:40 Or maybe, as we've been saying for centuries, it's made of cheese.
36:44 The Earth could have been purple before it turned blue and green.
36:48 A scientist has a theory that a substance existed in the ancient microbes before chlorophyll,
36:54 this thing that makes plants green, evolved on Earth.
36:57 This substance reflected the sunlight in red and mauve, colors that combined to give purple.
37:03 If this is true, the young Earth may have overgrown strange purple plants before all these green things appeared.
37:09 The highest mountain in the solar system is Olympus Mons on Mars.
37:14 It is three times higher than Mount Everest, the highest peak on Earth compared to the sea level.
37:19 If you were standing at the top of Olympus Mons, you wouldn't understand that you're on a mountain.
37:24 These slopes would be hidden by the curvature of the planet.
37:27 Astronomers have found a huge water reservoir in space, the largest ever detected.
37:33 It's a shame that it's also the furthest.
37:35 It's 12 billion light years away from us.
37:38 This water vapor cloud contains 140 billion times more water than all the oceans on Earth combined.
37:45 Venus rotates at its own pace, without rushing.
37:49 A complete rotation takes 243 terrestrial days.
37:52 And it takes the planet a little less than 225 terrestrial days to make the full rotation of the Sun.
37:58 This means that one day on Venus is longer than a year.
38:02 There is very little seismic activity inside the Moon.
38:05 However, small lunar earthquakes caused by the gravitational force of our planet
38:10 sometimes occur several kilometers below the surface.
38:13 Then, tiny cracks and fractures appear on the surface of the satellite, and gases escape.
38:19 Mars is the last of the four inner planets, which are also called telluric,
38:25 because they are made up of rocks and metals.
38:27 The heat of the Sun is under our feet.
38:30 Scientists have discovered that the core of the Earth is actually as hot as the surface of the Sun,
38:36 about 6,000 degrees Celsius.
38:39 One of the reasons why it's so hot down there is that the Earth is still losing heat
38:44 dating from its creation billions of years ago.
38:47 In addition, when an object as big as Mars hit the young Earth,
38:51 it not only created the Moon, according to a theory,
38:54 but it also melted the surface of the planet.
38:57 Much of this additional heat is probably still stored inside the core.
39:03 But there is no need to worry.
39:05 It is more difficult for us to access the core of the planet than to probe the surface of Pluto.
39:10 In fact, there is a good chance that we will never develop a technology
39:15 that will allow us to physically reach the core.
39:18 There is no air on the Moon.
39:21 But then how can there be rust?
39:23 Scientists have discovered the presence of hematite on the Moon, which is a kind of rust.
39:28 A NASA special research instrument examined the light reflected by the surface of the Moon.
39:34 It turned out that the composition of the poles of our natural satellite was very different from the rest of the Moon.
39:40 The surface is sprinkled with rocks rich in iron.
39:44 But without oxygen or liquids, rust cannot appear.
39:48 Solar winds add to the mystery.
39:51 They bombard the Moon with hydrogen.
39:53 But hydrogen makes the formation of hematite much more difficult.
39:57 Even if the Moon has no atmosphere, it still has traces of oxygen.
40:01 Its source is the high atmosphere of our planet.
40:04 The Earth also protects the Moon from almost 100% of solar winds, but not all the time.
40:09 And even if our natural satellite is completely dry,
40:12 there could be ice water in the shaded craters of its hidden face.
40:18 A day on Uranus lasts 17 hours, 14 minutes and 24 seconds.
40:24 But the planet has an inclination of about 98 degrees.
40:27 And that means that a season on the gas giant lasts 21 terrestrial years.
40:32 Mars has two moons, Phobos and Deimos.
40:37 In the 30 to 50 million years to come, Mars' gravitational forces will tear Phobos
40:43 and this will probably lead to the formation of a ring around the planet.
40:47 The Earth is the densest planet in the solar system.
40:52 In the centre of the Earth, the nucleus occupies 15% of the planet's volume.
40:56 It is made up of two parts, the external nucleus and the internal nucleus.
41:01 The internal nucleus is a solid ball made up of iron and nickel.
41:05 Its radius is 1220 km, which represents 20% of the radius of the entire Earth
41:11 and 80% of the radius of the Moon.
41:14 The external nucleus, with a thickness of 2400 km, is liquid.
41:19 It is also made up of iron and nickel, but it is not strong enough to be solid.
41:24 Mars houses the largest volcano in the solar system.
41:29 Although everything seems calm on Mars nowadays,
41:32 in the past, some kind of force caused the formation and eruption of huge volcanoes.
41:38 One of these volcanoes is Olympus Mons.
41:40 It is 26 km high, which is three times the height of Everest,
41:44 and 600 km wide, which is the size of Arizona.
41:48 The volcano has reached such a size because of the low gravity on Mars
41:53 and the lack of movement of the tectonic plates.
41:56 Gravity is not the same everywhere.
41:59 The rocks, metals and other minerals and substances that make up the planet
42:04 are tighter in the ground in some places than in others.
42:07 This has surprising consequences.
42:09 Gravity varies slightly depending on where you are.
42:12 You weigh 0.5% less at the equator than at the poles.
42:16 In most cases, this represents a difference of less than a kilo.
42:20 The altitude at which you are also has an effect.
42:23 So if you were at the top of Mount Everest, you would also weigh slightly less.
42:27 The most resistant living being on Earth is so small that you can't see it.
42:33 Tardigrades, also known as water bears,
42:36 are cute little creatures with eight legs and crushed heads
42:40 that are less than a hundredth of a centimeter.
42:42 Despite their microscopic size, they can survive almost everywhere.
42:47 They prefer damp moss or the bottom of lakes,
42:50 but they won't complain if you put them in a really uncomfortable place.
42:54 They can withstand extreme cold and incredible heat
42:57 and survive under enormous pressure and high radiation.
43:01 Some of these bears have even managed to survive without protection in space
43:05 for 10 days.
43:07 They manage all this by rolling in balls and hibernating,
43:10 which reduces their oxygen and food needs.