10 Strangest Planet Types Ever Discovered | Planetary science

[00:00:00]Just 64 light years from Earth, there is a planet where glass rains from the sky, about 200 lighty years away, there is another world where rock evaporates, rises into the atmosphere, and falls back as rain. And even within our own solar system, there are planets where diamonds rain deep inside. These are not ideas invented for science fiction. They are real planets. And these extraordinary conditions are based on actual observations and scientific models. When we hear the word planet, most of us picture a world like Earth, a solid rocky world with ground beneath our feet. Planets like these are called terrestrial planets. But terrestrial planets are only one of the many types of planets found in our galaxy. Even within our own solar system, we have two completely different categories. Gas giants and ice giants. And once we move beyond our solar system, the variety becomes far more extreme. There are super Earths and mini Neptunes. There are hot Jupiters orbiting so close to their stars that an entire year lasts only a few days. There are possible water worlds with oceans hundreds of kilometers deep, lava worlds covered by vast seas of molten rock, and planets traveling alone through the darkness without orbiting any star. These are worlds we could never have imagined simply by studying the planets around our own sun. In this video, we are going to explore the different types of planets found across our galaxy along with some of the strangest worlds science has ever discovered.

[00:01:43]>> [music] >> Hi friends, welcome to a new episode of science simplified for all. This video is arranged as a countdown ranking the different planet types according to how strange and extreme they are. Let us begin with the planet types found within our own solar system. As the countdown moves forward, the worlds will only become stranger. [music] Number 10, terrestrial planets.

[00:02:10]These are the planets most familiar to us. Solid worlds made mainly of rock and metal with a surface we could theoretically stand on. Their outer layers are generally composed of silicut rock while metals such as iron and nickel are concentrated towards the center, but the proportions can vary dramatically. Earth has a thick rocky mantle surrounding its metallic core.

[00:02:34]Mercury is almost the opposite with an unusually large ironrich core covered by relatively thin rocky layers. And some terrestrial planets may be far stranger.

[00:02:45]Theoretical models suggest that carbonrich rocky planets could contain enormous quantities of diamond deep inside them, perhaps even forming extensive diamond rich layers. [music] Number nine, gas giants.

[00:03:00]As we reach number nine, the solid ground beneath our feet disappears.

[00:03:05]Jupiter and Saturn are the gas giants of our solar system. Enormous planets made mainly of hydrogen and helium with no ordinary solid surface to stand on.

[00:03:16]These are the same elements that dominate stars. But Jupiter and Saturn never became stars because they are far too small to produce the pressure and temperature needed for sustained nuclear fusion. Despite their enormous size, gas giants can have surprisingly low average densities. Saturn is actually less dense than water. So, if an ocean large enough could somehow exist, Saturn would float in it. But the deeper we travel into a gas giant, the stranger it becomes. The pressure rises so dramatically that hydrogen is compressed into a dense liquid-like state. Deeper inside Jupiter, it may transform into metallic hydrogen, a bizarre form of hydrogen that conducts electricity like a metal.

[00:04:01]Gas giants may also contain a dense central region of heavier materials, but most of the planet is still hydrogen and helium.

[00:04:10]Number eight, [music] ice giants.

[00:04:14]Uranus and Neptune are the two ice giants in our solar system, but the name can be misleading. They are not giant frozen balls with solid surfaces made of ice. In fact, neither planet has an ordinary surface to stand on. And even if a solid core exists at the center, it would mainly be rocky rather than a huge block of frozen water. The word ice also has a broader meaning in planetary science. It does not refer only to frozen water. Volatile substances such as water, methane, and ammonia are also classified as planetary ices. The outer atmospheres of Uranus and Neptune consist mainly of hydrogen and helium with smaller amounts of methane. These outer regions are extremely cold with temperatures approaching -200° C. But deeper inside, the conditions are completely different. As pressure and temperature rise, water, ammonia, and methane may exist as a hot, dense fluid.

[00:05:17]Much of the mass of these planets is believed to consist of materials in such unusual states. And deep within these ice giants, something even stranger may be happening. Under immense pressure and temperature, methane and other carbonri compounds can break apart. The carbon atoms released from them are then squeezed together so intensely that they may form tiny diamonds. These diamond particles would sink deeper towards the center of the planet, creating what scientists call diamond rain. And this is not merely an idea invented for science fiction. When researchers recreated similar pressure and temperature conditions in laboratories, they successfully produced diamond particles from hydrocarbon materials. So deep inside Uranus and Neptune, diamonds may be falling even now. Number seven, super Earths and mini Neptunes. At number seven, we come to an unsolved mystery hidden within our own solar system. Earth is the largest rocky planet in our solar system. The next larger planets are Uranus and Neptune with nothing in between. But when we look at other star systems, planets within this missing size and mass range appear to be extremely common. They belong mainly to two categories, super Earths and mini Neptunes. The name super Earth often creates the wrong impression. It may sound like a planet that is better than Earth, more habitable and more suitable for life.

[00:06:47]But super refers only to its size or mass. A super Earth is larger or more massive than Earth, but smaller than Neptune. It could be rocky, have an atmosphere, or even contain liquid water. But the name itself guarantees none of these things. Many Neptunes also fall between Earth and Neptune in size, but they are usually less dense and surrounded by thick layers of gas. In simple terms, a super Earth generally leans more towards a rocky terrestrial planet, while a mini Neptune resembles a smaller version of Neptune. These two planet types are found throughout our galaxy, yet our own solar system contains neither of them. Why two of the galaxy's most common planet types are completely missing here remains one of planetary science's unanswered questions. [music] Number six, hot Jupiters.

[00:07:41]At number six, we find another oddity.

[00:07:44]Jupiter sized planets in places where gas giants are not normally expected to exist. Gas giants are generally thought to form far from their parent stars.

[00:07:55]Jupiter, for example, is so distant from the sun that one complete orbit takes nearly 12 Earth years. But some Jupiter-like planets orbit incredibly close to their stars. These are called hot Jupiters. Many complete an entire orbit in just 3 or 4 days, meaning a full year in that planet may last only a few Earth days. Most are also expected to be tidily locked with the same side permanently facing the star. As a result, their day sides can reach unimaginable temperatures. The most extreme example is Kelt 9b. The hottest confirmed exoplanet discovered so far.

[00:08:36]Its dayside temperature is around 4,300° C, hotter than the surfaces of most stars in the Milky Way. This places it in an even more extreme category known as ultra hot Jupiters. But Kelt 9b is not producing energy through nuclear fusion like a star. It is this hot because it orbits extremely close to a very hot parent star and remains constantly exposed to its intense radiation. Its night side is comparatively cooler, creating an enormous temperature difference that drives powerful winds through the atmosphere. Kelt 9b orbits at only 0.035 035 astronomical units from its star, roughly 1/10enth of Mercury's distance from the sun. It completes an entire orbit in just 1 and 1/2 Earth days. But this extreme closeness is also slowly destroying the planet. Every planet has a region around it called the ro lobe within which its gravity can hold on to surrounding material. If the planet's atmosphere expands beyond this boundary, the planet begins to lose control of the gas. Some may be pulled towards the star while some may be driven out into space by intense stellar radiation. This is exactly what is happening to Kelt 9b.

[00:09:55]Its atmosphere has expanded enormously and material is continuously escaping from the planet. One study estimated that at this rate, Kelt 9b could lose an amount of material equal to the entire mass of Earth every 30 million years.

[00:10:12]>> [music] >> Number five, water worlds. A planet is generally called a water world when water makes up a substantial part of its overall composition. This naturally raises a question. Does that mean Earth is also a water world? After all, oceans cover nearly 2/3 of its surface. The difference lies in the depth. Earth's oceans are only about 4 km deep on average. Even Challenger Deep in the Mariana Trench, the deepest known point in the ocean reaches only around 11 km.

[00:10:45]Earth itself has a radius of approximately 6,300 km. So although water covers most of the surface, it forms only an extremely thin layer and accounts for a tiny fraction of Earth's total mass. A true water world could be completely different. Its entire surface might be covered by one enormous ocean extending hundreds of kilometers deep.

[00:11:10]Water could make up a significant portion of the planet itself. And the deeper we travel into such an ocean, the stranger it becomes. The pressure near the bottom would be so immense that water could transform into exotic high-pressure forms of ice. Ice created not by extreme cold, but by crushing pressure. Scientists have already discovered several exoplanets that may belong to this category. Kepler 138 C and Kepler 138D are two possible waterorld candidates. By measuring their mass and size, scientists can calculate their average density. Their relatively low densities suggest that they may contain enormous quantities of water or other volatile materials. Some models indicate that water- richch layers could make up a large portion of their volume and extend thousands of kilometers into the planets.

[00:12:04]Number four, [music] lava worlds. Lava worlds are extreme versions of the rocky terrestrial planets we discussed earlier. When we heard the term lava planet, we may imagine a world covered with countless volcanoes. But a true lava world is far more extreme. large regions of its surface and in some cases nearly the entire surface may remain molten. Just as a water world may be covered by a global ocean, a lava world may be covered by a vast ocean of molten rock. Earlier we saw that when a Jupiter-like gas giant orbits extremely close to its parent star, it becomes a hot Jupiter. Similarly, when a rocky planet orbits close enough to its star, the intense heat can melt its surface and transform it into a lava world. In fact, Earth itself probably passed through a magma ocean phase shortly after it formed. Collisions during its formation, the sinking of heavy elements towards the core, radioactive decay, and enormous impacts released so much heat that much of Earth's surface may once have been molten. But as Earth gradually released that heat into space, its surface cooled and solidified into the rocky world we know today. A rocky planet orbiting extremely close to its star may never get that chance. Constant exposure to intense stellar radiation can keep large parts of its surface hot enough for rock to remain molten, creating vast lava oceans. One of the best known examples is 55 Kria, an extremely hot super Earth that may be covered by an enormous ocean of molten rock. It orbits its parent star at a distance of only 0.015 astronomical units, just 125th of the distance between Mercury and the sun.

[00:13:58]And it completes an entire orbit in less than 18 hours. In other words, one full year on 55 concrete lasts less than a single day on Earth. Number three, [music] rock rain planets.

[00:14:13]We have just seen how a rocky planet can become a lava world because these planets orbit extremely close to their stars. Many are expected to be tidily locked with the same side permanently facing the star. That side can become so hot that rock does not merely melt. it begins to vaporize. On Earth, water evaporates from the oceans and rises into the atmosphere as water vapor. On a lava world, molten rock can do the same thing, rising from the lava ocean as rock vapor. Meanwhile, the side facing away from the star remains much cooler.

[00:14:50]This enormous temperature difference can generate powerful winds carrying the vaporized rock from the scorching dayside towards the colder night side.

[00:14:59]There the rock vapor begins to condense.

[00:15:02]On Earth condensed water vapor falls as rain. But on this planet rock may fall from the sky as rain. This is what scientists describe as rock rain. One of the best known examples is K2141b.

[00:15:18]A tidily locked lava world candidate located just 200 light years from us.

[00:15:24]This planet orbits so close to its parent star that it completes an entire orbit in only 6.7 hours. But if that number alone does not reveal how unbelievably close the planet really is, let us understand it visually. What you see here is a correctly scaled model of our solar system. If this small yellow dot represents the true size of the sun, then this is the size of Earth's orbit.

[00:15:49]On the same scale, nearly 100 suns could comfortably fit side by side in the space between the sun and earth. Now, if we show the parent star of K2141b and the planets orbit in the same way, it would look like this. This is not because the star is unusually large. It is because K2141b orbits incredibly close to it. There is not even enough empty space between the stars surface and the planet to place another star of the same size. That is how closely K2141b circles its parent star. If you could stand on the planet and look towards the sky, the star would appear as a gigantic glowing sphere covering a large portion of your view. That is why the dayside becomes hot enough for rock to melt and even vaporize. When scientists modeled the temperature and atmospheric conditions of K2141B, their results suggested that rock could be raining on this planet even now.

[00:16:51]Number two, glass rain planets.

[00:16:54]Some exoplanets look incredibly beautiful from a distance. Only when we discover what is happening inside them do we understand how terrifying they really are. One of the best examples is HD189733b.

[00:17:09]It appears as a beautiful deep blue world almost like a calm planet covered with oceans. But that blue color does not come from water. It comes from clouds containing tiny glass-like silicut particles. The presence of these silicut particles is one of the features that makes this planet so unusual.

[00:17:28]HD189733b is a hot Jupiter believed to be tidily locked to its parent star with the same side constantly facing it. Its atmosphere is unimaginably hot. Under these conditions, silicates, minerals containing silicon and oxygen commonly found in sand, quartz, and glass can form tiny glass-like particles within the clouds. And the atmosphere itself is violently moving. The enormous temperature difference between the planet's dayside and night side generates winds reaching nearly 8,000 km per hour. That is roughly twice the speed of a typical rifle bullet. These winds carry the glass-like silicut particles through the atmosphere at extreme speeds. This is what is meant by glass rain. But the rain would not fall gently downwards as it does on Earth.

[00:18:21]The particles would be driven almost sideways across the planet by the violent winds. Now, imagine yourself inside that planet's atmosphere.

[00:18:29]Thousands of superheated glass-like particles would be racing sideways towards you faster than bullets. Within moments, they would tear through your body. That is how violent and terrifying the atmosphere of this beautiful planet really is. Yet from a distance, HD189733b appears to be nothing more than a calm and beautiful blue world. [music] Number one, rogue planets.

[00:18:58]So far, we have explored planets with diamond rain, lava oceans, rock rain, and glass-like particles racing sideways through the atmosphere. But all these worlds have one thing in common. Every one of them orbits a star. We normally think that orbiting a star is one of the most basic characteristics of a planet.

[00:19:18]But some planets orbit no star at all.

[00:19:21]They travel alone through the darkness of the galaxy, untethered to any parent star. These are rogue planets. They have no sun. There is no sunrise, no sunset, and no true daylight, only an endless night. Many rogue planets may have begun as ordinary members of planetary systems. During the early and chaotic stages of a star system, the gravity of a giant planet can fling a smaller world out of its orbit. A passing star may also disturb the system and eject a planet into interstellar space. Once expelled, that planet continues traveling through the galaxy alone, no longer bound to its original star. This is probably how many rogue planets are created. But some free floating planetary mass objects may form independently through the collapse of gas clouds in a process more similar to the formation of stars. Most rogue planets would be extremely cold and dark, but not all of them may be completely frozen inside. Young or massive rogue planets can retain heat left over from their formation. Rocky worlds may also continue generating internal heat through radioactive decay.

[00:20:33]Under the right conditions, a thick atmosphere could trap some of that heat.

[00:20:38]A deep layer of ice might also insulate a liquid ocean beneath the frozen surface. So even on a world traveling through eternal darkness, hidden oceans of liquid water may still exist deep below. Finding these planets, however, is extremely difficult because they produce almost no visible light. One of the most important ways to detect them is through gravitational microlensing.

[00:21:03]When a rogue planet passes between Earth and a distant star, its gravity briefly bends and magnifies the stars light.

[00:21:11]That temporary brightening can reveal an otherwise invisible planet. Young and relatively massive rogue planets can sometimes also be detected through infrared radiation because they still release heat left over from their formation. One example for a rogue planet is PSJ 318.5-22, a young free floating planetary mass object located about 80 lighty years away. Scientists have discovered several other rogue planet candidates as well, but these may represent only a tiny fraction of the true population. Some estimates suggest that the Milky Way may contain billions or perhaps even trillions of rogue planets. They may even outnumber the stars themselves.

[00:21:57]Yet, without a nearby star to illuminate them, most of these lonely worlds may remain hidden from us forever. Through this video, I hope you have gained a better understanding of some of the strangest and most extreme planet types found across our galaxy. If you enjoyed the video, please give it a like and share your thoughts in the comments and share it with friends who may also enjoy exploring the strange worlds beyond our solar system. Thank you.