00:00Pluto was once considered a major planet, but it was then classified in the category of dwarf planets,
00:07that is to say something too big to be an asteroid, but too small to be taken seriously.
00:13Not very nice.
00:14Recently, scientists have begun to discuss the mystery surrounding one of Pluto's moons.
00:20It turns out that it could be even cooler than we thought.
00:23We could have a system with two planets there.
00:26Pluto resides in the distant belt of Kuiper, a vast area of our solar system,
00:34like a large rocky banlieue located beyond the orbit of Neptune.
00:38It is filled with small icy objects, similar to Pluto, and bearing the name of Kuiper objects.
00:44These objects are the remains of the first days of our solar system,
00:48and they give us some clues about how it was formed.
00:51It is from there too that many comets come from.
00:54You already knew it was small, but did you know how much?
00:58Pluto has a width of about 2,250 km,
01:02about half that of the United States, and much smaller than our moon.
01:06Pluto's atmosphere is very fine, and is composed of nitrogen, methane, and carbon monoxide.
01:12A real treat for the nostrils.
01:14And it is also very cold, with average temperatures of about minus 234 ° C.
01:21Its orbit around the sun looks like an oval, and a year on Pluto lasts about 250 terrestrial years.
01:28Pluto also has a strange and unique retrograde rotation,
01:32because it is tilted on its axis, which means it turns to the side.
01:38If you were on Pluto, you would be surrounded by high icy mountains, valleys, plains, and craters.
01:45The sun would be very weak and distant, it would always be twilight.
01:49It is a very colorful planet, surprisingly.
01:51You would see a rainbow of pale blue, yellow, orange, and deep red.
01:56But the most adorable about Pluto is its famous heart, the Tombaugh region.
02:00Pluto was discovered very late, in the 1930s, much later than the other planets.
02:06At first, we thought it was the ninth planet in our solar system.
02:11However, the more we explored Kuiper Belt,
02:15the more we realized that it was filled with these medium-sized objects.
02:19We found four other small planets similar to Pluto.
02:22Eris, Ceres, Makemake, and Aumea.
02:26They all had the same characteristics.
02:29It was at this moment that we understood that Pluto belonged to a completely different family,
02:33and that we had created the category of dwarf planets.
02:39There are some differences between these two categories of planets.
02:42The first obvious difference is the size and mass.
02:45The major planets are much larger and more massive.
02:48They must also be spherical, while dwarf planets cannot be perfect spheres.
02:54They can have weird shapes, like Aumea, which is shaped like an egg, for example.
02:59Just like a normal planet, a dwarf planet rotates around the sun, but its orbit is not clear.
03:05It is full of debris and heteroclite objects.
03:08These are the only differences.
03:09This reclassification has therefore aroused a lively controversy.
03:13The English speakers have even invented a new term,
03:16to be plutoed, which means to be outclassed.
03:19Although it is sad that Pluto is no longer a major planet,
03:22we can console ourselves by telling ourselves that we have found a real family for it.
03:29Finally, when you stand on Pluto, you can see its five moons,
03:34Styx, Nix, Kerberos, Hydra, and the most mysterious, Charon.
03:39Charon is Pluto's largest moon.
03:41It was discovered in the 1970s thanks to NASA's New Horizons probe.
03:46The probe took a photo that revealed a moon with a fascinating and huge red-brown spot on its surface.
03:52It is a vast canyon that has nothing to envy to our Grand Canyon.
03:56It seems that Pluto and its moon both have interesting formations on their surface.
04:02Charon's particularity is that it is very large for a moon.
04:05It is about half the size of Pluto.
04:07Scientists therefore wonder, would Pluto be a two-planet system?
04:12The center of mass, or barycenter, of Pluto and Charon is outside Pluto.
04:18Normally, in the case of planets and their moons,
04:21it is the center of the planet itself that should be the center of mass, the moon orbiting it.
04:27But in the case of these two objects, it seems that they orbit each other.
04:31Binary objects are very common in the universe.
04:35These cosmic couples form as our moon formed, as a result of a giant impact.
04:40But double planets are extremely rare, and we have never discovered double dwarf planets.
04:46If the hypothesis is confirmed, it would mean that Charon is in fact the sixth dwarf planet.
04:51It will then be the first binary system of dwarf planets in history.
04:55But we have another candidate, the dwarf planet Eris and its moon, Dysnomie.
05:02The solar system is full of mysterious and fascinating moons.
05:07So fascinating that some of them could even be home to life.
05:11It's been a while since we've talked about microscopic life in space.
05:15Debates about the discovery of organic fossils on Mars have been going on for decades.
05:20With the development of our technology, we are finally on the right track.
05:24Here is Encelade, very popular since the arrival of the Cassini probe from NASA.
05:29Encelade is covered with a kind of snowy coat,
05:32which explains its unusual brightness and the presence of snowy craters.
05:36It is small, only about 500 km, and is mainly composed of rocks and ice.
05:42But in 2004, we discovered panaches of water spilling into the south pole of this moon.
05:47This means that there is liquid water under its icy surface.
05:51The reason is probably Saturn and its other big moon, Dione.
05:56Their gravitational dance creates tidal forces that bring heat and life to Encelade.
06:00Encelade is therefore a candidate for choice in the search for life in our solar system.
06:04Of course, life requires more than water, and we will not find animals or anything of the kind.
06:10But we could find microscopic organisms there.
06:13And that's really great.
06:17In fact, Saturn is winning the lottery in terms of the possible presence of life forms.
06:23For example, scientists had the crazy idea that Titan, another of these moons,
06:28could also shelter an extraterrestrial life.
06:31Titan is an icy satellite whose temperature is close to minus 179 degrees Celsius.
06:36Surprisingly, there are even lakes on its surface.
06:39But don't imagine classic water expanses.
06:42These lakes would not be filled with water, but with tannins or liquid methane.
06:46In 2005, NASA mentioned the possibility of a life feeding on chemical substances
06:52such as acetylene or hydrogen in the Titan lakes.
06:56Then, in 2010, NASA scientists went deeper into their research.
07:01And they discovered that there was a lack of hydrogen and acetylene in the Titan lakes,
07:06which suggests the possibility that something feeds on these substances.
07:10As a result, some dared to imagine methane-eating beings in the frozen lakes of Titan.
07:15In addition, they suggested that, if these creatures exist,
07:19they probably have cells much larger than those of terrestrial animals.
07:23So we could find there something much bigger than a simple microbe.
07:27Something like a small animal, for example.
07:31But Saturn is not the only one to be lucky.
07:34Triton is Neptune's big moon.
07:36And you guessed it, it's another candidate.
07:39The surface of this icy world is covered with nitrogen and its crust is made up of water ice.
07:44Once again, it is very cold there.
07:46And Triton is one of the favorite of geologists.
07:49Because it is part of the small number of moons that, in our solar system,
07:53have formidable active geysers.
07:56They reject gaseous nitrogen into space.
07:58It would be a beautiful spectacle if we could see it.
08:01These geysers mean that Triton has a secret source of heat.
08:05This means that, just like for Encelade, there could be liquid water under the surface of Triton.
08:10And if this place turns out to be home to life, we could find organic substances there.
08:18Unfortunately, it is not easy to send a mission to explore these celestial bodies.
08:22The only spacecraft we have sent so far is Voyager 2, in 1989.
08:29It takes us more time, money and technology to develop probes capable of traveling far
08:34and exploring the regions located beyond Mars.
08:37And even if we get there, it will take decades for these machines to reach these places.
08:42Anyway, let's hope that in the 21st century,
08:46we will finally be able to fully explore our solar system and all its wonderful mysteries.
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