Les scientifiques ont découvert la véritable raison pour laquelle Mars est devenue un désert aride et désolé, et c'est plutôt choquant. Il y a longtemps, la planète rouge avait des lacs, des rivières, et peut-être même des océans, mais quelque chose a causé la disparition de toute cette eau. Il s'avère que Mars a perdu son champ magnétique protecteur, ce qui a permis aux vents solaires de dépouiller son atmosphère au fil des millions d'années. Sans une atmosphère épaisse pour piéger la chaleur et empêcher l'eau de s'évaporer, la planète s'est lentement asséchée. Maintenant, tout ce qui reste, ce sont des plaines poussiéreuses, des canyons profonds, et de la glace gelée sous la surface. Mais si jamais nous voulons y vivre, les scientifiques travaillent sur des moyens de ramener une partie de cette eau perdue ! Animation créée par Sympa.
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FunTranscript
00:00Like the locomotive of a famous tale, the rover Curiosity of NASA bravely crossed the Gale Crater on Mars,
00:07trying to understand what could have happened billions of years ago for this planet to become a red desert.
00:13And it would seem that it finally fell on something.
00:17While life seems impossible today on Mars, it could be that there was, at a very distant time,
00:23a world closer to Earth, with a thick atmosphere, water, and even life.
00:29And it seems that things have only recently changed.
00:32Studies show that only 3 billion years ago, the northern hemisphere of Mars would have housed a stable ocean.
00:39On Earth, the Archean era was in full swing.
00:42Volcanoes were erupting, and life was taking its first steps.
00:45And maybe it was also taking its first steps on Mars.
00:48It was not an icy desert like Antarctica.
00:51There was a large amount of water similar to our oceans.
00:54This climate, close to that of Earth, extended the habitability period of Mars by about 500 million years,
01:00compared to what we thought until now.
01:03In other words, for half a billion years, Mars was exactly like our planet,
01:08with ideal conditions for the appearance of life.
01:11But something happened that changed things forever.
01:14The atmosphere became rarer.
01:16Mars lost its oceans, and became the cold and desolate place we know today.
01:22The mystery remained intact for a long time.
01:25But then Curiosity came across something interesting in the Gale crater.
01:30A vast basin on the surface of Mars where, billions of years ago, water flowed freely.
01:36It found carbonates, which could well inform us about the ancient climate of the red planet.
01:41These are minerals that form when carbon dioxide, or CO2, dissolves in water.
01:47This means that to create them, you need two things.
01:51A thick atmosphere and liquid water.
01:53On Earth, CO2 is very important because it helps to trap the heat of the sun in our atmosphere.
01:59This allows our planet to stay warm enough for life to develop.
02:04Plants consume this CO2 during photosynthesis,
02:07and create the oxygen that humans and animals need to breathe.
02:12On Mars, the presence of CO2 tells us that there was a functional climate system there.
02:17When CO2 begins to dissolve in water, it reacts with some soil minerals,
02:22such as calcium or magnesium, and creates carbonates.
02:25It's a bit like the formation of shells in the oceans here on Earth.
02:29But here, rocks are formed.
02:31And this discovery is huge.
02:33These carbonates are, in a way, the fossils of the ancient climate of the planet.
02:38They contain information about the conditions that reigned on Mars a very long time ago.
02:43By studying them, scientists can learn more about the past of the planet,
02:47and go back to the time when there was water.
02:50They can tell us about the evolution of the Martian atmosphere,
02:53show us if the atmosphere was hot or cold,
02:55if there was a lot of water, and what happened to the planet in general.
02:59Fortunately, Curiosity can study all this on site.
03:03It is equipped with an instrument that allows the analysis of samples,
03:06and a laser spectrometer.
03:09They allow scientists to conduct the investigation.
03:12The first is a mini-laboratory on wheels.
03:15It is able to heat samples of Martian rocks at extreme temperatures.
03:20These two ovens can heat up to almost 1000 degrees Celsius.
03:23This intense heat causes the release of the gases trapped in the rocks,
03:28which are like the old digital prints of the atmosphere of Mars.
03:31Once these gases are released, the spectrometer analyzes them in detail,
03:35reducing them to their smallest components.
03:38What scientists have discovered has shaken our hypotheses about the habitability of Mars.
03:43It turns out that not only was there water on this planet,
03:47but also that something led to its drying up, and to its gradual cooling.
03:52In other words, the water of Mars did not just disappear,
03:56it quickly evaporated in extreme conditions.
03:59So what happened?
04:01Astronomers have come up with two possible explanations.
04:04According to the first, Mars would have gone through periods
04:06sometimes wet, sometimes dry.
04:09The water did not last very long.
04:11It appeared suddenly, with periods where the planet dried up, then became wet again.
04:17The second possibility is more intense.
04:20The water that was there was incredibly salty and cold.
04:23Instead of being liquid, it was mainly frozen.
04:27The planet would then have been far too hostile to life as we know it,
04:31with conditions too extreme for anything to survive.
04:35These two possibilities unfortunately mean that Mars has never been a pleasant place and full of life,
04:41as some hoped.
04:42In any case, not on the surface.
04:44This does not mean that underground life could not exist.
04:48It remains a possibility.
04:49And to find out more, we must continue to look for clues about the presence of water.
04:54Indeed, after years of exploration,
04:57scientists have just made a stunning discovery.
05:00Under the rocky surface of the red planet,
05:03there is a reservoir of liquid water.
05:05Real water, this time.
05:08Not ice cubes, or atmospheric steam.
05:11But it is located kilometers below the Martian crust.
05:14This discovery comes from data collected by the NASA InSight lander.
05:19He spent four years listening to the subtle earthquakes of the planet.
05:23Yes, there are earthquakes on Mars.
05:26He analyzed more than 1,300 earthquakes.
05:29Thanks to him, scientists were able to map the way seismic waves move on the planet.
05:36And they thus discovered pockets of liquid water buried between 9.7 and 19.3 km below the surface.
05:44Not a single lake, but several basins.
05:48These methods are the same as those used on Earth to find water, oil and gas.
05:54They were able to reconstruct the Martian underground system.
05:57Indeed, part of the planet's water escaped into space when Mars lost its thick protective atmosphere.
06:04However, this discovery tells us that all the water has not disappeared,
06:08but that it has simply sunk into the depths of the ground where it is still today.
06:14So close to the goal, but still out of reach.
06:17It's a big step forward.
06:19Water is the most important molecule when it comes to shaping the fate of a planet.
06:23In addition, even if we said that Mars did not have life before,
06:28this does not remove the possibility that some forms may indeed exist today.
06:33If liquid water still exists in the depths of the planet, could microbes hide there?
06:39Life as we know it cannot survive without liquid water.
06:43The idea of life on Mars has therefore become more than ever plausible.
06:47But there is a hiccup.
06:48If this water may seem to be a jackpot for future Martian colonization projects,
06:53it will not be easy to reach.
06:55To say that drilling at a depth of 9.7 km is not an easy task is an euphemism.
07:01Know that here, on Earth, the deepest drilling we have done is about 12 km.
07:07It was in the framework of the project COLA Super Deep Borehole.
07:11And this project has pushed current technology to its limits.
07:14Intense heat, pressure, equipment failure, everything has gone through it.
07:19On Mars, it would be even crazier.
07:21The environment there is much colder.
07:23The atmosphere extremely tenuous and the infrastructure non-existent.
07:27This would make any drilling mission extremely difficult.
07:31To reach the water reservoirs buried so deeply,
07:34we would need to carry out a specialized equipment in one way or another.
07:38This equipment should be able to withstand extreme cold,
07:42low pressure and different gravity.
07:45And all this should of course work remotely and, preferably, not deteriorate.
07:51And the operation would require tons of energy.
07:54And yes, it is possible that we can only achieve this in the future,
07:58when we will have automated systems or astronauts on Mars.
08:02This is not an easy task, even for the most ambitious billionaires.
08:06For now, what these reservoirs hide remains a mystery.
08:10And this is not the only riddle.
08:12As we mentioned, Mars hides one of its greatest secrets under its frozen pole.
08:17Another vast lake of liquid water dives deeply.
08:20A radar revealed it by scanning the ice cap of this region which bears a name to be laid outside.
08:25It is strange that the water remained liquid at temperatures so low.
08:29It is probably due to the geothermal heat that reigns under the surface.
08:33And there could be life there too.
08:35They therefore plan to probe this lake first.
08:38A much easier operation.
08:40Curiosity's work is incredible.
08:42And it continues to help us peel the layers of the ancient Martian climate,
08:46delivering us new pieces of the puzzle that represents the history of our neighbor.
08:51This could help us avoid similar mistakes in the future.