00:00The scientists came to find something that could become the plan B of humanity.
00:05A planet rocheuse with a real atmosphere,
00:09located in the exact zone where liquid water could exist.
00:12And this discovery changed everything.
00:15For years, the scientists of space
00:18have a really frustrating scheme.
00:21They're constantly seeing the planet rocheuses
00:23at about the size of the Earth,
00:25in this ideal area around other stars,
00:28where the temperature would allow the liquid water to exist.
00:32The scientists call it the habitable zone,
00:35but it's also a chic way to say
00:38that it's not too close to the star, nor too far.
00:41It's like for your coffee,
00:43not too hot to be eaten,
00:44but not too cold to be eaten.
00:48And every time they find a planet in this window,
00:51it enthousiasme everybody
00:53because it's exactly the kind of conditions
00:56that we would hope to find out
00:57to dénicher the life ailleurs.
01:00But in looking at the more close,
01:03the planet has actually no atmosphere.
01:07There's no air, no clouds,
01:09practically nothing to protect the radiation of the stars.
01:13Imagine a house in a perfect place,
01:16in a perfect place,
01:17with an ideal meteorite,
01:18but without no toits,
01:20no port.
01:23This is what these planets
01:24have been revealed to be.
01:25These are empty particles
01:26in the right place.
01:29Nothing protects the interior.
01:34But this black series is finished.
01:38These astronauts have found an atmosphere
01:41of the sky.
01:42This world is called LHS 1140 b,
01:46and it is located at about 48 years later.
01:51One year later,
01:52it's simply the distance
01:54traveled by the light in one year.
01:56And the light goes incredibly fast,
01:59about 186 000 miles per second.
02:02So,
02:0348 years later,
02:04it's almost impossible to imagine.
02:06It's just that it's very far.
02:09We will not visit it too soon.
02:12This planet is about 5,5 x plus lourde
02:15than ours,
02:16and about 1,75 x plus large.
02:19One version
02:20slightly inflated of the Earth.
02:22Not an enormous amount of gas,
02:24but it's always rocheuse,
02:26simply more large and more lourde.
02:29It's almost impossible to see
02:30a little red red red red red red red
02:31every 25 days.
02:34It's almost impossible to see
02:36the entire year
02:36that's only one month
02:37at least.
02:39And it receives
02:40about 40%
02:41of the solar light
02:42received by the Earth.
02:43So,
02:44it's like
02:45one single day
02:46every year.
02:48Every year.
02:49This time,
02:49no one has searched
02:50the usual signs
02:51of an atmosphere
02:52like the vapor
02:53or the carbon dioxide
02:54or the carbon dioxide.
02:55Because
02:56at 48 years later,
02:58these elements
02:59are much too low
03:00to be detected.
03:02It's like trying
03:03to feel the kitchen
03:04of someone
03:04at four feet
03:05and the other.
03:06It's like
03:07an odor
03:07but impossible
03:09to see it seriously
03:10as far as possible.
03:12So,
03:13the main researcher
03:14wanted something
03:15totally different.
03:17Repellen
03:18the helium
03:18that
03:19comes out from the
03:19atmosphere
03:20of the planet
03:21and goes out
03:22in space.
03:24Imagine
03:24instead of
03:27searching
03:27an immobile
03:28inside a house
03:29for a kilometer
03:30since more than a kilometer,
03:31he was looking for the smoke that was out of the chimney.
03:34It was much easier to see.
03:37If the planet had really an atmosphere,
03:40the X rayons and the ultraviolet of the star
03:42would propel the helium directly from its superior surface.
03:46And an instrument installed in Chile,
03:48called Winnerhead,
03:50could really capture this helium
03:52when it came out.
03:54Some experts doubted that it worked,
03:56because it was a risker.
03:58But it worked!
04:01They pointed the telescope towards the planet
04:04during a transit,
04:05i.e. when she passed directly
04:07from our point of view.
04:10And the signal became net and incontestable.
04:14L'hélium flottait like a halo.
04:19But the most interesting thing happened.
04:22This same night,
04:24by pure chance,
04:25a second planet smaller
04:27of the same system
04:28is also passing before the star.
04:31The other one,
04:32called LHS-1140C,
04:35is more close to the star,
04:36and receives so much more radiation.
04:39We would even expect to see
04:41even more of the helium
04:42to escape,
04:43since it is more bombardable.
04:47But...
04:48nothing.
04:49And this comparison is very important.
04:52It shows that the helium signal
04:54of the planet B
04:55is not a simple bug
04:57in the data.
04:58It is a precise signal,
04:59appropriate to this planet.
05:04Then, in 2025,
05:06the team
05:06again pointed the telescope
05:08towards LHS-1140B.
05:11And this time,
05:12the helium had disappeared.
05:14It was no longer
05:15at least,
05:15at least not in a detectable way.
05:19At first,
05:21it could seem to be a bad news.
05:22Like if the atmosphere
05:23had perhaps disappeared
05:25for good.
05:26But the scientists
05:27think in reality
05:28that it is the point
05:29the most passionate
05:30of all this discovery.
05:32And here is why.
05:34We assume that this planet
05:36and all its stellar system
05:38have more than 3 billion years
05:39and the helium
05:41is an incredibly light gas
05:43and it is not in place
05:45after the escape
05:46from space.
05:47It derives away
05:48and disappears.
05:50So,
05:51if nothing on the planet
05:52did not replace this helium,
05:54it would no longer
05:55after 3 billion years.
05:58The fact that the helium
05:59is appeared
05:59and disappeared
06:01and could probably
06:02appear,
06:03means that something
06:04under the surface
06:05of the planet
06:06is constantly
06:07and constantly
06:08renewing the reserves.
06:10The scientists
06:11describe this
06:12as a planet
06:13which breathes.
06:14This suggests
06:15an atmosphere
06:16in the clouds.
06:18The helium
06:19is evaporated
06:20while a gas
06:21more lourd,
06:22perhaps
06:22of the vapor
06:23of the surface.
06:30In talking about gravity,
06:32here is another
06:33indice
06:33that supports this idea.
06:35Like this planet
06:36is more lourde
06:36than the Earth,
06:37its gravity is also
06:38stronger.
06:39And a more powerful
06:41And a more powerful
06:41gravity
06:41will prevent
06:42the gas
06:43to escape
06:44in the space.
06:48The helium
06:49is
06:50away from the summit.
06:56It doesn't prove
06:57that there is
06:58oxygen,
06:59oil
06:59or
07:00oil
07:00oil
07:00but it means
07:01that the planet
07:02has a lot of
07:03attractions
07:03gravitational
07:04to retain
07:05the more lourdes
07:07if they are present.
07:08Now we have
07:09the question
07:10of the water.
07:11Because it is really
07:12what everyone wants to know.
07:14The scientists
07:15calculated the size
07:16and the exact mass
07:17of the planet
07:18and discovered
07:19that it is a little
07:20less dense
07:21than a solid boule
07:21of water.
07:23According to an estimate,
07:25between 9 and 19%
07:27of the total mass
07:27of this planet
07:28would be made
07:29of water.
07:31It is enormous.
07:32And more
07:34than the part
07:35of the water
07:35in the mass
07:36of the Earth.
07:37So there is
07:38a real possibility
07:40that a vast
07:40ocean
07:41can be found.
07:42But
07:43let's clear,
07:44no one
07:45ever observed this
07:46It is a
07:47calculation
07:47based on the mass
07:48and the size
07:49and not something
07:50seen directly
07:51by a telescope.
07:52But why
07:53this planet
07:54has survived
07:54when many others
07:56have failed?
07:57The small planet
07:58around the small
07:59clouds are generally
08:01very bombarding
08:02by the radiation
08:03at the beginning
08:04of their existence
08:05and often lose
08:06their atmosphere
08:08even if they end
08:08later in the
08:09good zone
08:10of temperature.
08:12This planet
08:13seems to be
08:13a rare
08:16of the
08:17sea.
08:17The planet
08:18has been
08:19very close
08:20to the most
08:20of the millions
08:20of years.
08:22The planet
08:22has been
08:23very close
08:23to avoid
08:24the worst
08:24of the radiation.
08:27L'astronome
08:28qui a découvert
08:29cette planète
08:29en 2017
08:30a résumé
08:31la grande question.
08:33Est-ce simplement
08:35une roche nue
08:35qui rejette
08:36parfois un peu
08:37de gaz,
08:38lequel disparaît
08:39aussitôt ?
08:42Ou y a-t-il réellement
08:43une atmosphère stable
08:44qui s'échappe lentement
08:46comme cela arrive
08:47parfois aussi
08:48sur Terre ?
08:49Pour l'instant,
08:50personne n'en est sûr.
08:52Mais nous allons
08:52bientôt le découvrir.
08:54Cette planète
08:55vient d'être placée
08:56en tête de liste
08:57d'un projet commun
08:58de Hubble
08:58et du télescope spatial
09:00James Webb,
09:01conçu spécialement
09:03pour rechercher
09:04des atmosphères
09:04sur de petites
09:05planètes rocheuses
09:06comme celle-ci.
09:07Au cours des quatre
09:08ou cinq prochaines années,
09:10les scientifiques
09:10surveilleront de près
09:11la réapparition
09:12du signal d'hélium.
09:14Ils chercheront aussi
09:15plus profondément
09:16des signes de vapeur d'eau
09:18et d'autres gaz
09:19plus bas,
09:19près de la surface.
09:22S'ils trouvent de l'eau,
09:24ce sera pratiquement
09:24la confirmation
09:25qu'il existe
09:26sur cette planète
09:27une atmosphère réelle,
09:29stable et durable.
09:30Sous-titrage
09:30Sous-titrage
