00:00This planet, yes, this one, should not exist, but it exists.
00:05Recently discovered, it revolves around a star much smaller and less luminous than our sun.
00:10And yet, it is huge!
00:13Such a tiny star could not have created it.
00:16It's a bit like finding an ostrich egg in a henhouse.
00:21A team from the University of Penn State has developed a tool,
00:24the Planet Detector of Habitable Zones.
00:27It is an instrument supposed to find planets around dim and cold stars.
00:32It is connected to a large telescope in Texas.
00:35The tool examines the light of the stars in what is called the near infrared,
00:40that is, beyond what our eyes can see.
00:43This gadget can detect when a star changes speed because of a planet.
00:47If the movement of a star changes slightly,
00:49it means that there must be a gravitational attraction nearby.
00:53A few years ago, this technique allowed to find the first exoplanet
00:57known around a star similar to our sun.
01:00Today, we have improved this method to take more precise measurements.
01:04Our main goal is to find planets similar to Earth.
01:08They must be rocky and located in habitable zones,
01:12that is, in regions where liquid water could exist.
01:15The Doppler technique is not yet very effective to find this kind of world.
01:20But it works quite well for cold and dim stars.
01:23This is how we discovered the impossible LHS 3154 b.
01:31Planets are generally formed in gas and dust disks.
01:34Imagine a flat cloud in rotation, composed of tiny particles.
01:39These particles gather and stick to each other.
01:42After a while, they end up combining to form a solid nucleus.
01:47This is how a planet begins.
01:50Once the nucleus is there, it attracts more dust and even gas,
01:54for example hydrogen and helium.
01:56But it is not easy to create a planet in this way.
01:59It takes a lot of things, mass and materials.
02:02This process is called the nucleus accretion.
02:05Stars are a precious help in this process.
02:08Normally, large stars have a large gravity,
02:11which allows them to accumulate all the materials necessary for the formation of planets.
02:15But the star we recently discovered is not very big.
02:18It is nine times smaller than our sun.
02:21Such a small star should not have a disk large enough to allow the formation of a heavy planet.
02:27For this, its disk should have been at least ten times larger.
02:31But this heavy planet, LHS 354 b, does exist.
02:38This mysterious planet is 13 times heavier than our Earth.
02:41Its size is similar to that of Neptune.
02:44It is about fifty light-years away from us, in the constellation of Hercules.
02:48Which, in space terms, is very close.
02:51The planet is also very close to its star.
02:54It completes a year in almost four days.
02:57This discovery led scientists to review their ideas on how planets and stars are born.
03:04New theories are emerging, such as those of gravitational instability.
03:08According to this theory, instead of assembling little by little,
03:11the matter of the disk collapses all at once, creating immediately a planet.
03:16But even with this theory, it is difficult to explain how such a heavy planet can form without a really massive disk.
03:23We will need time to shed light on all this.
03:29This is not the first planet that makes us doubt our theories.
03:32Recently, scientists have discovered another planet called Allah.
03:37This planet is orbiting around a star called Baekdu.
03:41And, just like the previous one, it should not really exist.
03:45It is far too close to its star.
03:47Stars change a lot in their lifetime.
03:50Normally, a star becomes big when it prepares to leave this world.
03:54This is what is called the red giant stage.
03:57Such a star tends to destroy or repel neighboring planets, creating a huge mess.
04:03Since it revolves around a red giant, Allah must have been swallowed or destroyed a long time ago.
04:08But it is still there.
04:10Baekdu has already begun to burn helium and has become smaller than expected.
04:14But Allah does not seem to care.
04:18Scientists call Allah the forbidden planet.
04:21His discovery questions what we thought of the survival of planets near aging stars.
04:27And we have two theories.
04:29According to the first, Baekdu was once composed of two stars.
04:32A white dwarf and a red giant.
04:34Allah was in orbit around the two.
04:36And they merged before the red giant took its full size.
04:40If Allah was able to survive, it was because of the additional helium of the white dwarf that prevented the red giant from growing excessively.
04:48According to the second theory, Allah would have formed from the debris created during the fusion of the two stars.
04:54In this case, Allah would be a very young planet in orbit around an old star.
04:58Astronomers continue to study Allah and look for other planets of this type.
05:05Another strange planet, named LTT 9700M109B, scares us a little because it is too bright.
05:12This planet reflects 80% of the light of its star.
05:16Ordinary mirrors reflect between 85 and almost 100% of the light.
05:22Which means that this mysterious planet must have the appearance of a rough mirror with reflections of aluminum or silver.
05:29This planet is also the size of Neptune.
05:31It is located 260 light years from us and was discovered by the TESS probe of NASA.
05:37It makes a complete rotation around its star in just 19 hours.
05:41It is very close to its star and therefore extremely hot, reaching temperatures near 2000 ° C.
05:49Normally, planets as close to their star lose their atmosphere and turn into bare rocks.
05:55But this one happily decided to do it to its head.
06:01This time, we know the secret of its survival.
06:04It owes it to shiny metallic clouds composed of glass and titanium.
06:08These clouds make titanium rain on the hot surface of the planet.
06:13They reflect a lot of light, which prevents the planet from becoming too hot and losing its atmosphere.
06:20A bit like a mirror shield.
06:22The size of this planet also surprised scientists.
06:25It is much larger than Earth.
06:27Generally, planets that are so close to their star are either very, very large gas giants or small rocky planets.
06:35Well, this planet is a small gas giant.
06:38Scientists did not expect it to survive so close to its star.
06:42It is the brightest planet ever discovered.
06:45Even brighter than Venus.
06:47Despite its appearance, it is probably not suitable for life due to its extreme temperatures and its strange metallic rain.
06:57Finally, our last case is a planet called WASP-107b.
07:02Scientists discovered it using the James Webb Space Telescope.
07:06It is located about 200 light years from Earth, in the constellation of the Virgin.
07:11It is also very fast.
07:13It loops an orbit around its star in just 6 days.
07:17This is a super-Neptune-type exoplanet.
07:20It looks like Jupiter in some respects, especially in its size and its very high temperatures.
07:25But the main difference is that it is much lighter, weaker and less dense.
07:31It is the least dense planet we have discovered so far.
07:34After some additional research, we also discovered that it has a tail composed of helium, which it releases during its transit.
07:42It slowly loses its atmosphere due to the extreme ultraviolet radiation of its star.
07:47And so its tail looks exactly like that of a comet.
07:51A comet of Jupiter.
07:55But this is only the beginning.
07:57The low density of this planet, its plushy appearance, has allowed astronomers to study its atmosphere in detail.
08:03And they discovered surprising elements, like water vapor and clouds,
08:08made up of fine particles of silicate, which look like very fine sand.
08:13Its high star does not emit much light at high energy.
08:16But as WASP-107b is very dense, this light can penetrate deeply into its atmosphere.
08:22It results from sulfur dioxide, this smell that comes out when you scratch a match.
08:28In other words, it is a cloudy planet on which it rains sand and smells like matches.
08:34Researchers believe that sand clouds in its atmosphere are formed in the same way as clouds on Earth.
08:40They simply contain particles of sand instead of water droplets.
08:44These sand droplets condense, fall, turn into silicate vapor in the hot layers of the planet,
08:51then rise to form clouds again.
08:55But this planet could not form where it is.
08:58According to astronomers, it probably got closer to its star little by little, attracted by a heavier neighbor.
09:05And it follows a retrograde orbit, that is, it turns in the opposite direction of the rotation of its star.
09:11All these discoveries change the way we understand planets and their atmospheres.
09:16And so, we can better understand the mysteries of our own solar system.
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