Every Star That Might Have Aliens Explained In 18 Minutes

[00:00:00]Proxima Centauri is the first name on the list and it is the closest star to our sun just 4.25 lighty years away. It is a red dwarf so faint you cannot see it with the naked eye despite being our nearest stellar neighbor. It is small, barely more than a tenth the mass of the sun, and it burns cool and dim and red.

[00:00:22]Orbiting inside its warmth is a world called Proxima B, a rocky planet roughly the size of Earth, sitting in the zone where liquid water could theoretically exist. On paper, it is one of the best candidates we have ever found. In reality, it is a planet under siege. The problem is the stars temper. Red dwarfs like Proxima are cooler than the sun, so their habitable zone sits far closer in.

[00:00:48]Proxima B orbits about eight times closer to its star than Mercury orbits ours. At that distance, the planet is locked in the stars gravitational grip.

[00:00:58]It is titally locked, meaning one side faces the star forever in permanent scorching daylight, while the other side is trapped in eternal frozen night.

[00:01:08]Imagine a world where the sun never rises and never sets. where you could walk from a blazing desert into a black frozen wasteland by crossing a single line on the ground. But the real danger of Proxima isn't its heat or its darkness. It is the flares. Red dwarfs are violent, unstable stars that erupt constantly. In 2014, NASA caught a red dwarf firing off a flare 10,000 times more powerful than anything our sun has ever produced. Proxima does this regularly, drowning its planet in ultraviolet and [clears throat] X-ray radiation that could strip an atmosphere clean off a world molecule by molecule.

[00:01:49]Astronomers remain drawn to Proxima B, despite real fears that these stellar flares could tear its atmosphere away entirely. It is the closest hope we have, orbiting the most short-tempered neighbor imaginable. Trappist one comes next and it is a star with a whole family of worlds. It sits about 40 lighty years away. An ultra cool red dwarf barely larger than the planet Jupiter. A tiny dim ember of a sun.

[00:02:18]Packed tightly around it is something we have found nowhere else. Seven Earth-sized rocky planets orbiting so close together that the entire system would fit comfortably inside the orbit of Mercury. If you stood on one of them and looked up, you would see the other planets hanging in the sky, close enough to make out their surfaces. It is a solar system in miniature, a clockwork of worlds spinning around a star that could fit inside our largest planet.

[00:02:46]Four of those seven planets are the reason astronomers keep coming back.

[00:02:51]Trappist, 1D, E, F, and G all orbit at distances where liquid water could, in theory, exist on their surfaces. These are not gas giants or barren rocks. They are rocky earth-sized worlds sitting in the temperate band around their star.

[00:03:08]And they are considered some of the most compelling candidates for life we have ever cataloged. Of the seven planets D, E, F, and G are thought to be the most Earthlike, and their discovery in 2017 made headlines around the world. But orbiting a red dwarf this closely comes at a price. These planets are almost certainly tidily locked, frozen in place with one face toward the star. And like every red dwarf, Trappist one is prone to flaring, bombarding its tightly packed worlds with radiation.

[00:03:42]The very thing that makes this system so easy to study, its compactness, is also what puts every one of its planets directly in the firing line. LHS140 is the third star and it hosts a world that might be an ocean hidden under a lid of ice. It is a red dwarf located about 48 light years away. And the planet that has scientists talking is called LHS114b.

[00:04:13]It is a super Earth larger and heavier than our planet. And for years its nature was a mystery. Was it a rock? a gas shrouded mini Neptune, something else. Then the James Webb Space Telescope turned its eye toward it.

[00:04:28]Recent observations from Web suggest LHS 1114b could be a water world wrapped in a nitrogen-rich atmosphere, making it one of the most promising habitable zone planets we know of. Picture a planet where the surface facing the star is warm enough to melt a bullseye of open ocean into a global sheet of ice. A single circular sea staring up at a red sun while the rest of the world stays frozen solid. A world that isn't quite Earth and isn't quite ice moon, but something in between. What makes LHS1140 stand out is that it may sidestep the worst of the red dwarf curse. A planet with a thick protective atmosphere and enough water to spare can survive the flares that would sterilize a drier world. If an exoplanet forms far enough from a flaring red dwarf and starts with far more water than Earth, it can hold on to enough of it to remain viable despite the radiation. LHS1140B might be exactly that kind of survivor.

[00:05:35]Red dwarfs deserve a stop of their own here because nearly every star so far has been one, and there is a reason for that. But it comes with a warning. Up to 85% of all the stars in the Milky Way are red dwarfs, and as many as 40% of them may host Earth-sized planets in their habitable zones. They are, by sheer numbers, the most common place life could possibly exist. If life is out there, statistically, it is far more likely to be orbiting a small red star than a sun like ours. But red dwarfs are also the most dangerous hosts imaginable. and they stay dangerous for a terrifyingly long time. Our sun was violent in its youth, throwing off flares for its first half billion years before settling down. Red dwarfs are different. They have an extended active youth and stay violently active far longer than sunlike stars, pumping out x-rays and ultraviolet radiation for billions of years. a planet orbiting, one has to endure that assault, not for a few hundred million years. But for a stretch of time longer than complex life took to appear on Earth. And there is a second quieter danger because these planets are tidily locked. They rotate slowly and slow rotation tends to produce a weak magnetic field that can shut down entirely.

[00:07:02]That matters because a magnetic field is a planet's shield. Without it, the stellar wind strips the air away into space. It is exactly what happened to Mars. Still, it may not be hopeless.

[00:07:17]Newer climate models show that winds in a thick atmosphere can spread the stars heat around a tidily locked planet, preventing the dark side from freezing solid. and simulations suggest even oceans are possible under the right pressure. Kepler 186 is the next star and it holds a small piece of history.

[00:07:38]It is a red dwarf about 500 light years away and its planet Kepler 186f was one of the first Earth-sized worlds ever confirmed inside a stars habitable zone.

[00:07:51]Not a super Earth, not a puffed up mini Neptune, but a rocky planet close to the size of our own, sitting in the temperate band where water could pool on the ground. For a long time, it was the closest thing to a genuine twin of Earth's situation that we had found. It is faint. It is distant, and we may never see its surface in any detail. But it was the proof of concept, the first solid sign that worlds like ours sit in the habitable zones of other stars waiting to be found.

[00:08:25]Everything on this list in a sense follows from planets like Kepler 186F, showing us that Earth's situation is not unique. TOI715 is a more recent name, and it is one of the reasons this search keeps accelerating. It is a red dwarf and its headline world to715b is a super earth sitting squarely inside the conservative habitable zone. The tighter safer band where the case for liquid water is strongest. What makes to715 matter isn't just the planet. It is how it was found. It was spotted by TESS, a planet hunting telescope built to scan the nearest brightest stars, which means to 715b is close enough and wellplaced enough to become a real target for follow-up. It made the cut in the latest catalog of the most promising rocky worlds for life alongside the famous names. This is what the modern hunt looks like. Not one lucky discovery, but a steady stream of rocky, temperate worlds turning up around nearby red dwarfs. Each one a fresh place to point our best instruments. Taeti is the seventh star, and it is a genuine change of pace, because it is not a red dwarf at all. It is a sunlike star only about 12 light years away. Bright enough to see with the naked eye, emitting a light spectrum similar to our own sun, but about 25% smaller. This is the kind of star science fiction always imagined we would find life around. Not a dim red ember, but a warm yellow sun much like the one you see every day. Astronomers have found four Earth-sized planets orbiting it. among the smallest ever detected around a nearby sunlike star.

[00:10:22]And two of them, Taetti E and F, sit in the habitable zone. And because Taetti is a true sunlike star, its habitable zone is far enough out that its planets are not tidily locked. Unlike the worlds around Proxima or Trappist one, these planets would turn, giving them proper days and nights instead of one frozen face and one burning one. But Taetti hides a threat the red dwarfs don't. The star is surrounded by a massive disc of debris, an asteroid and comet belt with far more material than our own, which likely bombards its planets with impacts and lowers their chances of staying habitable.

[00:11:06]It is a calmer star with a more violent neighborhood, a peaceful sun ringed by a shooting gallery. Gisa 667C is the eighth name, and it may be the strangest place on this list to imagine standing. It is a red dwarf just over a third the mass of the sun, about 22 lighty years away. And it is not alone.

[00:11:28]It is the third star in a triple star system. Around this one small red star, astronomers found something record-breaking. A system with at least six planets, three of them super Earths, sitting inside the habitable zone at once. The first system ever found with a fully packed habitable zone. Three potentially habitable worlds orbiting a single star with no room left for more.

[00:11:54]And the sky above those worlds would be like nothing on Earth. From one of these planets, the two other suns of the system would appear as a pair of brilliant stars, bright enough to see in daylight, and at night, they would cast as much light as a full moon. But the same rules apply. All three habitable zone planets are expected to be tidily locked, each holding the same face toward its red sun forever. It is a system that shatters the idea that habitable worlds are rare, three of them crammed around one dim star under a sky lit by three suns. Gissa 581 is the ninth star, and it is one wrapped in an argument that has never fully been settled. It is a red dwarf about 20 light years away, and for years, it was one of the most famous names in the search for alien worlds. The reason is a planet that may or may not exist. Glee 581G was announced in 2010 and once topped the list of the most promising potentially habitable worlds ever found.

[00:13:01]But within weeks, other astronomers began casting doubt on whether it was real at all. It sat right in the middle of its stars habitable zone, a nearperfect candidate. And then it seemed to dissolve into the noise of the data. A ghost planet that scientists have been arguing over ever since. The system holds other rocky candidates orbiting the same red star. And GISA 581 remains one of the most studied planetary systems in the sky. It captures something true about this entire search. The signals are faint.

[00:13:35]The planets sit at the very edge of what our instruments can detect. And sometimes the most promising world of all turns out to be a flicker in the data that may never have been there. The orange dwarfs are the 10th entry and they may quietly be the best bet of all.

[00:13:52]These are the K-type stars sitting between the harsh red dwarfs and stars like our sun. And astronomers have a nickname for them. They call them Goldilocks stars because they burn their fuel slower than the sun, staying stable far longer while keeping their flare activity low and their habitable zone wide enough to avoid tidal locking.

[00:14:15]Think about what that combination means.

[00:14:18]A red dwarf gives you countless chances, but bathes its planets in radiation and locks them in place. A sunlike star is calm, but doesn't live all that long by cosmic standards. An orange dwarf splits the difference almost perfectly. It is gentle enough to spare a planet's atmosphere, bright enough to keep its worlds spinning freely, and it burns for tens of billions of years. These stars, along with the sunlike F and G types, are the traditional focus of the search, precisely because they stay stable long enough for life to emerge. If red dwarfs offer the most lottery tickets, the orange dwarfs may offer the best odds on each one. K2-18 is the 11th star and it is the one that recently set the entire field on fire. It is a red dwarf about 111 light years away. And its planet K2-18b is a strange kind of world. It is far larger than Earth, about 2 and a half times its radius and nearly n times its mass, sitting in an odd category between a rocky planet and a small Neptune.

[00:15:27]Scientists think it might be something remarkable. A Heisian world, a planet covered by a liquid ocean beneath a thick hydrogen-rich atmosphere, a completely different kind of habitable world than Earth. And then came the headline that stopped everyone. Using the James Webb Space Telescope, astronomers reported detecting dimethyl sulfide in its atmosphere, a molecule that on Earth is produced almost exclusively by living things, mainly marine phytolankton, calling it the strongest evidence yet that life might exist on another planet. But this is where caution has to enter. The claim is fiercely contested. A later NASA analysis found no conclusive evidence of the molecule and other studies showed the same gas can form without any life at all, even appearing on a cold, lifeless comet. K218b is not proof of life. It is the closest we have come to asking the question for real and a reminder of how hard the answer is to pin down. Tea Garden Star is the last name on the list, and it may be the most Earthlike of them all. It is a tiny ancient red dwarf about 12 lighty years away. So faint and so cool that astronomers did not even discover it until 2003 despite it sitting almost in our backyard. It is one of the smallest stars known, roughly 10 times less massive than the sun with a surface temperature of only about 2,700° C. And it is old. The system is estimated at around 8 billion years, nearly twice the age of our own solar system, which means any life there would have had almost double the time Earth has had to arise.

[00:17:18]Orbiting this dim old ember are two worlds, Tea Gardens star B and C, and they are extraordinary. Both have a minimum mass close to Earth's. Both are likely within the habitable zone, and they are among the most Earthlike exoplanets ever discovered. Planet B in particular has been rated as 95% Earth similar on the Earth similarity index.

[00:17:42]One of the highest scores ever recorded for a world beyond our solar system.

[00:17:47]Because the star is so faint, planet B receives almost exactly the same energy Earth gets from the sun, while planet C receives around 40% closer to Mars. But the same red dwarf problems apply here, too. Both planets orbit their star in just a handful of days, and both are almost certainly tidily locked with one face held permanently toward the star.

[00:18:11]Their fate rests entirely on their air.

[00:18:15]Habitability models show that surface liquid water could exist on both worlds across a wide range of atmospheres, which makes them some of the most attractive targets we have for searching for signs of life. Whether they have held on to that atmosphere across 8 billion years under a star that has been flaring the entire time is the question no telescope has yet been able to