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.
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