A Tour of a TRAPPIST-1 Analogue

TRAPPIST-1 is one of the few exoplanet systems we know of currently that both gets a ton of hype and is actually deserving of that hype. It has seven Earth-sized planets, three of which are in the habitable zone, where temperatures are right for liquid water to exist, as well as planets both interior and exterior to the habitable zone, so we really get a wide range of planetary environments here. Of course, TRAPPIST-1 is a very small red dwarf, so all seven planets are closer than Mercury is to the Sun, and are so close to one another they'll appear roughly as large in each other's skies as the Moon does from Earth, and also all seven planets are tidally locked to the star. Though, as I talked about in a previous video, tidal interactions between the TRAPPIST-1 planets likely means they're only tidally locked sometimes, and the day and night hemispheres actually do change places on timescales of years to centuries. Check out my video The Chaotic Rotations of the TRAPPIST-1 Planets for more information about that. But anyways, obviously orbiting a red dwarf has a few problems for habitability, tidal locking slash chaotic rotation aside. Red dwarfs are better than larger stars at stripping away planetary atmospheres, especially when they're young. Importantly, this does not mean it's impossible for planets around red dwarfs to host atmospheres. Look at LHS-1140b, K218b, L9859d, and Anipotia as a few examples of mini-Neptunian super-Earth-sized planets with atmospheres around red dwarfs. But TRAPPIST-1 is scientifically interesting because, even if its planets turn out to be airless uninhabitable rocks, which is seeming more and more likely that will be the case, though is not confirmed yet, that still gives us a ton of information on what the typical red dwarf system looks like. TRAPPIST-1 gives us examples of hot, temperate, and cold rocky planets around red dwarfs at once, and they all transit and are able to be characterized, which is a valuable baseline for determining how other red dwarf systems might look. So far, however, we've yet to find a true analog of TRAPPIST-1 with a similar number of planets on similar orbits. But we have gotten fairly close. And this is where the main subject of this video, SPECULOOSE-2, comes into play. SPECULOOSE-2 is another very small red dwarf star, just 12% the mass of the Sun and 0.1% its brightness, 105 light years away from Earth. TRAPPIST-1, for comparison, is 9% the mass of the Sun, 0.05% its brightness, and 40.6 light years away from Earth. Meaning these two stars are very similar. The TRAPPIST and SPECULOOSE telescopes are also often used together and have the same goal of finding planets around ultra-cool red dwarf stars. TRAPPIST-1 can technically also be called SPECULOOSE-1 because of this, making it and SPECULOOSE-2 not only very similar in properties, but discovered by pretty much the same telescopes. So far, however, the planetary systems of TRAPPIST-1 and SPECULOOSE-2 are pretty different, but again, do share some important similarities. Both systems have transiting planets, meaning the planets pass directly in front of their star from our perspective, and SPECULOOSE-2 is actually the dimmest star to be observed to have transiting planets by the test telescope. Though SPECULOOSE-2 only has three planets, two confirmed and one recently discovered new candidate, there's still a surprising amount of interesting stuff to talk about. So let's first go over everything we know about the SPECULOOSE-2 planets, and how they compare to the TRAPPIST-1 worlds, and see what conclusions we can draw about red dwarf systems based on this. SPECULOOSE-2b is the first planet of the system, taking 2.7 days to orbit it. This planet is too close to the star to be in the habitable zone, making it similar to TRAPPIST-1b or c. However, it's significantly more massive than both of those planets, with a mass only recently determined by transit timing variations a few weeks ago of 2.2 times the mass of Earth. So this is a pretty large super-Earth. Because it transits, we also know its radius, and it's about 32% wider than Earth. For those who don't know, transit timing variations occur when a planet's transit occurs slightly earlier or later than usual, caused by very minor changes in its orbit influenced by other planets in the system. SPECULOOSE-2b exhibits TTVs because of the existence of the habitable zone planet SPECULOOSE-2c, and since we know how far away those two planets are from one another, it's possible to determine how large they both would need to be to explain the observed variations. However, even for accounting for the gravity of these two planets, SPECULOOSE-2b and c were still exhibiting excess transit timing variations, suggesting the existence of a third, previously undetected planet in the system. We'll talk about that after we go over a bit more about Planet B. Though SPECULOOSE-2b does transit from our perspective, currently this planet has not been observed with enough detail for us to get information about its environment beyond its mass and radius. This is partially because this is a fairly new world, and was only found in 2022, so the schedules simply haven't yet worked out to characterize it. However, it is very comparable to the smaller TRAPPIST-1b. The two have similar separations from their stars, 0.11 AU for TRAPPIST-1b compared to 0.018 AU for SPECULOOSE-2b. But since SPECULOOSE-2 is brighter than TRAPPIST-1, it's likely that SPECULOOSE-2b is of similar temperature to or hotter than TRAPPIST-1b, but again that's currently speculation because we don't have any temperature measurements for it. We do, however, know with decently high confidence that TRAPPIST-1b is an airless world with no significant atmosphere, as James Webb observations have suggested. Given a similar temperature and orbit around a similar star, it's a strong possibility that SPECULOOSE-2b could be airless as well. However, TRAPPIST-1b is only 1.37 Earth masses compared to SPECULOOSE-2b's 2.2. Larger planets do have an easier time holding onto atmospheres, but there are too many unknowns about this planet and also generally how red dwarfs affect atmospheres in general that we can't make any conclusions beyond this. It's worth noting here that TRAPPIST-1c, though it does have some good evidence of being airless as well, has not been fully confirmed as airless, and a thin, oxygen-rich atmosphere still remains a tentative possibility as of the time I'm making this video. Again, nothing confirmed, but if we assume the optimistic scenario for TRAPPIST-1c, maybe some kind of atmosphere isn't off the table for SPECULOOSE-2b. But that's complete speculation for now. Something a bit more clear-cut, however, is SPECULOOSE-2d, the second planet in the system. As of the time I'm making this video, this planet candidate was discovered just a few days ago on September 4th, 2026, so this is all extremely new information. This was the planet I mentioned earlier as potentially making up for the excess transit time and variations of the other planets. That's also why it remains a candidate. Right now, there's no direct evidence for the existence of this world, only indirect evidence based on the movements of its two neighbors. That being said, it is pretty strong indirect evidence, and I wouldn't be surprised if this planet was real. SPECULOOSE-2d is by far the smallest planet of its system, just 24% the mass of Earth, only a bit more massive than Mars, or just over a tenth the mass of SPECULOOSE-2b. If it exists, it takes 4.4 days to orbit the star, a similar orbital period to TRAPPIST-1d, though because the star is brighter, this planet is still too close to be in the habitable zone. So far, transit has not been observed, so this planet's radius is unknown, but it's likely very small, given its small mass. TRAPPIST-1 doesn't really have a direct analog to this planet. The only one similar in mass, TRAPPIST-1h, is significantly colder, and so not really useful for guessing details about its environment. So let's look at another planet from a different system, PROXIMA-d. PROXIMA-d, of the PROXIMA Centauri system, is about 26% the mass of Earth, making it very similar in mass to SPECULOOSE-2d, and one of the smallest planets found outside the solar system along with it. It takes 5.1 days to orbit PROXIMA-sen, again similar to SPECULOOSE-2d, and PROXIMA-sen is extremely similar in brightness, 1.5% the brightness of the sun, making PROXIMA-d a very good analog of this planet. These two worlds are similar in mass, temperature, and orbit around a similar star, so it's a fair assumption that they may have similar environments. PROXIMA-d has an estimated equilibrium temperature, ignoring any unknown environmental effects that would change this, of about 188 degrees Fahrenheit, or 87 Celsius. Because SPECULOOSE-2d was discovered literally less than a week ago, we don't know what temperature it may be, but something similar to PROXIMA-d is a possibility. However, given its small size and its orbit around a red dwarf, there's a pretty good chance this planet is going to be an airless rock, like a larger version of Mercury. SPECULOOSE-2d is a pretty good example of a planet TRAPPIST-1 doesn't really have a good example for, despite how useful of a baseline it is, so studying this planet, and of course confirming its existence, could help fit a gap in our knowledge for worlds of this type. It's currently unknown if this planet transits, since current telescopes weren't sensitive enough to see it, but if it does, it could be characterized as our observational capabilities increase. Now let's talk about the habitable zone planet, SPECULOOSE-2c. This planet is of similar size to B, around 2.28 Earth masses, making it potentially the largest one in the system, though that number is uncertain, and the highest possible mass for B overlaps with the smallest possible mass for C, so we don't currently know for certain which one is larger. But it is worth noting that based on that 2.28 number, SPECULOOSE-2c is more massive than TRAPPIST-1d, e, and f combined. It was discovered in 2022 along with B, so again not many observations have been done on it, except for another recent 2026 paper which searched for exomoons around this planet. This paper, linked in the description, was authored by David Kipping, who you might know from the Cool Worlds YouTube channel, and a search for moons around SPECULOOSE-2c was conducted. Because this planet takes just 8.4 days to orbit the star, it was unlikely that any exomoons were going to be here, and this is what the paper found. Using James Webb, they observed 12 transits of SPECULOOSE-2c, and looked for signs of any changes that could indicate the presence of a moon. None were found, ruling out any moons around this planet larger than 10% the radius of Earth. This means that if SPECULOOSE-2c has any moons, they must be smaller than Earth's moon, or smaller than other bodies like Rhea and Umbriel. So, no moons were detected here, but based on the planet's shore orbit, it was unlikely anyways, but this actually still gives us a lot of information. This specific exomoon search proves James Webb is capable of seeing exomoons around small planets similar to the ones we have in our solar system, which could be used for more successful exomoon searches in the future. Basically, SPECULOOSE-2c was used as a test, and moons weren't expected to be found here anyway, but it was an important test nonetheless. Anyways, yet again, we don't know the exact details of SPECULOOSE-2c's environment, but a high mass and lower temperatures do increase the chances of it having an atmosphere. How much they increase it is unknown, and there's still a chance it could be airless. A lot of this was already covered in a previous video I made with Jchoke, and you should check out, but basically, even if SPECULOOSE-2c does end up having an atmosphere, just being in the habitable zone doesn't automatically make it a potentially habitable planet, and there are a few problems it may have. Specifically, this high mass likely means that when SPECULOOSE-2c formed, it was covered in a global magma ocean for around 50 million years. Based on a third paper in the description, which ran models about this, depending on the mass of the planet, this could result in any water this planet formed with being blasted into space, leaving behind an extremely thick oxygen-dominated atmosphere, significantly thicker than Venus' and rendering the planet uninhabitable. However, this paper was made before the planet's mass was known, and different masses lead to different outcomes. Luckily, since we now know this planet's mass, we can see which scenario is the most likely. The smallest mass the paper modeled was about 2.2 Earth masses, very close to SPECULOOSE-2c's true mass. In the 2.2 Earth mass models, this oxygen buildup scenario actually didn't occur at all, but that's because all the oxygen was blasted into space along with the water, leaving a dry, barren planet behind. Also, tidal interactions from SPECULOOSE-2b could heat up the planet a lot more, similar to how Io is heated up by Jupiter and the Galilean moons, potentially creating a hot, volcanic world. Though this is speculative and based on models rather than actual observations, it may be a possibility that SPECULOOSE-2c is a dry, volcanic world, either airless or with a volcanically created CO2 atmosphere. Currently, no observations have been done to see which scenario is the case, or if there's another scenario we haven't thought of that could be a possibility, so SPECULOOSE-2c's environment currently remains a mystery. So SPECULOOSE-2 and TRAPPIST-1 are starting to paint a picture of what most red dwarf systems may look like. Though most planets have high chances of being airless, scenarios where these worlds are volcanically active and have atmospheres are not off the table yet. Unfortunately, both systems will need to be studied a lot more before we can make any definitive conclusions, but what we already know so far suggests that red dwarf systems can still be extremely interesting, even if it's all airless rocks. I'll be making more videos about these systems as we find out more, and hopefully there will be a lot more to talk about in the future. A lot of the discoveries about SPECULOOSE-2 are very recent, and there's still a lot more to see. But that's where I'll end this video. Hopefully we can find out more about SPECULOOSE-2, the sibling of TRAPPIST-1, soon. Thank you for watching. If you enjoyed, check out my other videos about exoplanets and space exploration.