I have a number of things to say about Teegarden’s Star and its three interesting planets, but I want to start with the discovery of the star itself.
Here we have a case of a star just 0.08 percent as massive as the Sun, an object which is all but in brown dwarf range and thus housing temperatures low enough to explain why, despite its proximity, it took until 2003 to find it.
Moreover, conventional telescopes were not the tools of discovery but archival data. Bonnard Teegarden (NASA GSFC) dug into archival data from the Near-Earth Asteroid Tracking program, surmising that there ought to be more small stars near us than we were currently seeing. The data mining paid off, and then paid off again when the team looked at the Palomar Sky Survey of 1951. This was a team working without professional astronomers and telescopes.
Image: Teegarden’s Star was subsequently identified in astronomical images taken more than 50 years ago. Credit: Palomar Sky Survey / SolStation.com.
That it took until 2019 to announce evidence of planets reflects the fact that for some time, we had trouble even coming up with a workable parallax reading, one that finally produced a distance of 12.497 light years. There are no transits at Teegarden’s Star, so the discovery data on the first two planets came through radial velocity studies conducted with the CARMENES instrument at the Calar Alto Observatory in Spain. In 2024 a third planet was found, likewise by RV.
Teegarden’s Star compels attention because of those planets, and in particular Teegarden’s Star b, which orbits just inside the habitable zone with an orbit lasting about five days. Its minimum mass, calculated from the radial velocity data, is 1.05 times that of Earth, but recall that because of the limitations of the RV method, we can’t know the orbital inclination of a world that is likely larger. The primary is relatively quiescent by red dwarf standards, and indeed produces flares that would not be problematic if planet b retained an atmosphere.
That last note is important, because the whole question of how long the planets of young red dwarfs retain an atmosphere is crucial. Teegarden’s Star is about eight billion years old and, as I mention, comparatively calm. But young red dwarfs can spit out enormous flares and present serious problems for atmospheric gases, to the point that the atmospheres may be depleted or destroyed altogether. We need to come to grips with the possibility that red dwarfs may simply be inhospitable to life, a notion skillfully dissected by David Kipping in a recent paper that I plan to address in the near future.
For now, though, let’s take a brief look at a new paper from Ryan Boukrouche and Rodrigo Caballero (Stockholm University) and Neil Lewis (University of Exeter). The authors tackle climate and potential habitability of Teegarden’s Star b, noting that its proximity puts it in the catalog for study by next-generation observatories. The team uses a three-dimentional global climate model (GCM) to study habitability, including position in the habitable zone and the question of surface climate if there is an Earth-like atmosphere.
The interest in Teegarden’s Star draws not only from its Earth-mass planets – which Boukrouche and colleagues see as prime fodder for future telescopes like the ESO’s Extremely Large Telescope and its Planetary Camera and Spectrograph – but the effect of flare activity on atmospheres. The authors assume that Teegarden’s Star b is tidally locked given its tight orbit (4.9 days) around the primary. They consider values for surface albedo which approximate first an ocean-dominated surface and then a surface dominated by land masses. Here the discussion reaches this conclusion: “Although the sensitivity to surface albedo is… relatively small, it illustrates that the habitable zone does depend on factors intrinsic to the planet, not just on orbital parameters.”
The results indicate that this intriguing planet may be habitable under these atmosphere assumptions, but if so, it is still close to the inner edge of the habitable zone. Indeed, of two different orbital distances chosen from earlier papers investigating this planet, one produces a runaway greenhouse effect that would prevent the presence of liquid water on the surface. Fittingly, the authors are sensitive to the fact that the habitability question hinges upon the configuration of their models. Citing studies of TRAPPIST-1, they note this:
…different GCMs configured to simulate the same planet can produce a range of climates and circulation regimes (presumably owing to differences between the parameterizations included in each model). For example, models capable of consistently simulating non-dilute atmospheres may explore the possibility that under a range of instellation values, the planet’s atmosphere might be in a moist greenhouse state (Kasting et al. 1984) instead of a runaway, where water builds up enough that the stratosphere becomes moist, driving photodissociation and loss of water to space.
Installation is critical. The classic problem: We need more data, which can only be supplied by future telescopes. Teegarden’s Star remains highly interesting, but if we have yet to nail down the orbital distance of a planet so close to the inner edge of the habitable zone, we can’t yet make the call on how much light and heat this planet receives. And the authors themselves point out that the origins of nitrogen on Earth are not completely understood, which makes guesses at its abundance in other worlds’ atmospheres problematic.
Image: Even in our local ‘neighborhood,’ the data on Earth-mass planets is paltry, and our investigations rely heavily on simulations with values plugged in to gauge the possibilities. New instrumentation will help but it’s sobering to realize how far we are from making the definitive call on such basic issues as whether a given rocky world even has an atmosphere. Image credit: Inductiveload – self-made, Mathematica, Inkscape. Via Wikimedia Commons.
Let me just suggest that this is where we are right now when it comes to key questions about life around nearby stars. Plugging in the necessary data on any system takes time and, when it comes to Earth-mass planets around red dwarfs, the kind of instrumentation that is still on the drawing boards or in some cases under construction. Given all that, we’re going to have quite a few years ahead of us in which we’re constructing theories to explain what we see without the solid data that will help us choose among myriad alternatives.
The paper is Boukrouche, Caballero & Lewis, “Near the Runaway: The Climate and Habitability of Teegarden’s Star b,” accepted at The Astrophysical Journal Letters. Preprint available.
Even under perfect conditions, the spectrum of this star will barely allow terrestrial photosynthesis. Either the local life would need to be able to use much longer wavelengths for photosynthesis, or just sip the available energy with the much lower blue light available. It is the opposite of macroalgae in the sea, where red algae at depths can still access the blue light needed for photosynthesis that penetrates clear water. If photosynthesis is unavailable, then life will be chemotrophic and anaerobic by default, even after 8bn years of evolution. If complex life evolved, it would be slow-moving, perhaps even dominantly sessile like plants, and limited to habitats where chemical energy was available. Would a planet still have active ocean vents or volcanoes to provide that energy?
If there were any life, it would be very interesting to study the ecosystems and energy flows of such a world. Would it mimic some of our abyssal oceans or crustal life, or have evolved biology and forms very different from terrestrial life?
A world that has developed for 8 billion years in its own environment would not have developed anything near terrestrial photosyntesis. I do understand your point but its easy to assume earth as a sort of standard. If there is life then it would have started and developed within its own limits and would evolve to maximize the use of its environment just life on earth has with its own environment.
If energy is scare instead of slow moving it might spend alot of time “charging” up on energy and then live fast in bursts. Like lizards are letargic when its cold. I moved Vipers in late autum that I would not dare to get close to in summer.
@Martin
Wouldn’t motil animals have to be in sync for this to work? Otherwise the animals that are active while their prey is not would wipe out their prey, and then themselves. The prey would have to make themselves invulnerable while inactive. Perhaps it would be like daytime and nighttime active animals. One is active while the other sleeps, yet both types have evolved.
@Alex
True, but they might not be animals. The fact that earth has this strict separation could be by chance. They might be mobile plants or “plantimals”, They could live by storing sugar from slow but steady photosyntesis and when they are filled up (or rather by some external stimuli) they start to have a mating frenzy where they run around to find a suitable mate.
Some (all modern?) corals has symbiosis with algae. Give them a stable environment for some 10th of millons of years and they might turn into a algimal.
@Martin,
I cannot think of any terrestrial animal that can fully power itself with symbiotic algae or incorporating chloroplasts. These are purely additions. Corals and sea slugs are primarily feeders of other organisms.
The reason is simple. Photosynthesis is a surface phenomenon. Scaling in size squares the dimension in surface, but cubes the mass. Therefore, animals would need to be either unicellular or more like plants with a high surface area to volume form. Preying on sessile primary producers or other motile animals is the most efficient way to acquire energy and mass for growth and reproduction. [At least on Earth.]
However, I accept that more exotic life forms may evolve to best make use of the dimmer, redder light of M dwarfs.
Teegarden’s Star has a surface temperature of 3000K, which is a warm white. Apparently this is a good color temperature for flowering plants.
As an aside, I wish space artists would consider the color temperature of a star when illustrating red dwarf stars. They’re not red. The only one who’s consistently good at this is Robert Hurt from Caltech/IPAC.
That said… spectral blanketing in M dwarfs can be significant, especially towards the blue. Maybe plants can evolve to make photosythesis work with slightly longer wavelengths?
As for the planet being on the inner edge of it’s HZ – so is the Earth. I think the bigger issue here is the early evolution of the primary; it could have blasted the planet’s atmosphere away early in its evolution.
Here’s a recent paper on compact planetary systems around red dwarfs:
Born Dry or Born Wet? A Palette of Water Growth Histories in TRAPPIST-1 Analogs and Compact Planetary Systems
Howard Chen, Matthew S. Clement, Le-Chris Wang, Jesse T. Gu
https://arxiv.org/abs/2510.12794
At FrankH
Actually, it isn’t. The light-harvesting molecule in green plants is sensitive to blue and red light. It is the trapping of these wavelengths that result in the reflected light from the leaves appearing green to our eyes. This is why efficient plant lighting uses red and blue LEDs, which gives these indoor farms a magenta-looking light.
Our sight is limited to what we receive through 3 different wavelength-sensitive cones. Some people have 4 different cones and can discriminate far more colors. Insects that visit flowers can usually see UV. If you view flowers under UV light, they look very different with patterns that insects can see, but we cannot. Other animals see further into the near IR.
There are different core compound assemblies for light trapping, which have shown capabilities to harvest light in the red end of the spectrum only. Some unicellular organisms can photosynthesize in the light of hot rocks in the ocean depths. IDK is they are effectively only primary producers, or whether this supplements a chemotropic metabolism.
As we know this shifting of wavelength absorption is possible, it is probable that photosynthesis on such dim, red stars can work, although the extractable energy is lower than on Earth. What color the “leaves” of such plants would be is a matter for speculation. Obvious colors may be tempered by other requirements, such as cooling and signaling to some animals that they may need for reproduction. What our human eyes see might be very different from the wavelengths that are absorbed and reflected, and perceived by the local fauna.
If dense “foliage” exists on such worlds, we may determine their color with very high resolution telescopes, such as those using the SGL as a focus for a “primary lens” with a diameter of the sun.
Hi Alex
Could the higher particle flux provide an energy source for making oxygen via breaking up water? We know the particle flux on Europa’s ice provides both O2 and H2O2 in sufficient amounts to provide oxidants to the ocean below, if the down-flow rate by solid-state convection is reasonably vigorous.
On Earth the O2 created by photosynthesis would double its level in 3 million years if it wasn’t for exposures of fossil carbon via erosion – the biosphere recycles what it uses, so only fossil carbon can be a net sink. That gives you some idea of the production rate in the present day.
@Adam
It would depend on teh rate. I did the calculations for Europa and the rate of O2 production is very low. On Earth, photolysis of water is a tiny fraction of the O2 from photosynthesis.
But strong UV emissions could change that rate. However, that effect may be balanced by the UV breaking up organic molecules making life more difficult. Life may have to live beneath the surface of the land or in the ocean depths. In a recent short story collection I read, life on a habitable planet around a red dwarf star lived beneath teh surface, but quickly emerged to catch organisms on the surface and then drag them below the surface to digest them. Were these inspired by the Sarlacc on Tatooine?
All I would say is that life is very adaptable, as we have seen on Earth over its history. Evolution, while constrained in some ways, can produce some very strange life forms. What might evolve on a red dwarf might be like analogs of those we see on Earth, or conceivably very different.
While physical forms and behavior can fascinate the naturalist, it is the fundamental biology that would be very intriguing to me. Would they be analogs of terrestrial biology, or very different? It is a pity I will never know. [However, experiments using AI to help design different biologies might provide a window into what is possible, and hence to look out for as we search for life in the universe.]
The 1997 and 2002 images of Teegarden’s star are substantially brighter than the 1951 and 1989 images. I have determined this by comparison with nearby stars, because it is clear that the two later images are ‘deeper’ (longer exposures) than the two earlier ones. Perhaps this is because the sensor was more sensitive to the red end of the spectrum in the latter two, but I am only speculating here. I do know the Palomar Sky Survey always took two images, one on red-sensitive and one on blue-sensitive emulsion plates so some color information was captured on every object visible on both. Whether something like this was going on in the ’97
and ’02 images I don’t know.
At any rate, it appears Teegarden is much brighter in the last two images than the first two. It’s not likely both the latter images coincidentally caught the star in a flare outburst. Maybe this star is a long-term variable?
Hi Paul
Another very interesting red dwarf Star here to study and follow up on. It sure is similar to Trappist one in Mass. I need to read the paper and the kippling one too.
Thanks Edwin
Retention Of Surface Water On Tidally Locked Rocky Planets In The Venus Zone Around M Dwarfs.
https://astrobiology.com/2025/05/retention-of-surface-water-on-tidally-locked-rocky-planets-in-the-venus-zone-around-m-dwarfs.htm.
I could imagine a large dark side icecap with a pacific size convection under it and subduction near the twilight zone. Thus creating huge volcanic mountain ranges in the twilight that keep a dense atmosphere locked into the dark side. The Ocean under the ice would have plenty of life from the spreading mid ocean ridges vents.
Maybe that’s how life started on earth, since all of the evidence from the ancient oceans has been recycled into the earth at least 18 times …
Seems someone has corrupted the link, so here is the main: https://arxiv.org/abs/2505.13066
Teegarden’s is an example of a very common type of stellar system. I call it a Jupiterian system as it consists of similar-sized bodies packed closely around their primary. From what I’ve read, the planets migrate in to form a resonance chain or near resonance chain. The inner planets form from the inner part of the planetary disk so have fewer volatiles, but as you go further out the planets migrate in from much further out so have a much higher proportion of ice.
The smaller a red dwarf is the longer it takes to reach its main sequence position. Teegarden’s star being so small, it would take a full billion years to reach its main sequence position, so the planets around it would have had a steam atmosphere for a good portion of this time. This atmosphere would have been subject UV, X-rays and intense flares, stripping off oceans worth of water. Photo-disassociation and the resolution Hydrogen loss will result in a very oxidizing chemistry if there is any atmosphere.
If Teegarden’s b is the least likely of the 3 planets to have a lot of water to start with, so I would expect if it has an atmosphere, it would be CO2, SO2 and if had had any bodies of liquid, they would of sulfuric acid. (Think of somewhere between Venus and Io.)
Teegarden’s c looks more promising to me even though its instellation is only 1/3 of b’s. It would presumably start with more volatiles, but subject to less intense, UV, X-rays and flares, and the atmosphere would condense out earlier than b’s, if b’s condensed out at all.
It’s also thought to be a bit smaller than b, so it’s more likely to be Earth-size. Also, glaciation does not occur in a runaway manner on tidally locked planets. As the planet gets colder (less moisture in the air), the high albedo cloud deck under the substellar point shrinks and eventually disappears counteracting the increase of albedo from ice formation.
We should check the exoplanets circling Teegarden’s Star for alien windmills…
https://astrobiology.com/2025/10/wind-power-as-a-technosignature-on-m-dwarf-planets.html
Wind Power As A Technosignature On M-dwarf Planets
By Keith Cowing
Status Report
Research Notes of the AAS
October 20, 2025
We suggest that the large-scale deployment of wind turbines on an M-dwarf planet could produce observable technosignatures.
Motivated by observations of hypersonic wind velocities on WASP-127 b, we note that the atmospheres of such planets could serve as vast reservoirs of energy for an extraterrestrial civilization.
A large-scale deployment of wind turbines in a hypersonic environment would produce heated shock waves in the hypersonic stream, cause strong frictional heating from the rotation of the blades, and be a source of infrared radiation.
We mention possible scenarios that could lead to the deployment of wind turbines on a gas giant and also note that similar features could exist on terrestrial M-dwarf planets.
The idea that aerodynamic peculiarities could be a technosignature is worth keeping in mind as ground- and space-based exoplanet observations continue to improve.
Wind Power as a Technosignature on M-dwarf Planets, Research Notes of the AAS (open access)
https://iopscience.iop.org/article/10.3847/2515-5172/ae13a7
Astrobiology, SETI
But what if their ETI forbids this technology? Maybe they are flyers and are concerned about the accidental deaths of those being shredded by such wind turbines. Or perhaps there is economic and political action against such devices but in favor of burning carbon compounds that can be extracted from the planet’s crust. Or perhaps they worry these turbines might be detectable and make the ETI civilization a target for galactic predators. Or perhaps life has adapted to these winds, and extracting this wind energy reduces the mass and biodiversity of the biosphere.
Alien civilization is sooo complex.
;-)
Interesting that Venus showes the same side of itself when closets to Earth. Teegarden’s b and c are ten times closer when the bypass each other at 1.88 million miles ever 13 days. Even being deep in the gravity well of Teegarden’s star I would be surprised if they were both tidally locked.
At the very least, the strong periodic tidal interaction should keep the planets more seismically active, increasing the possibility of hydrothermal vents. Also some lovely volcanoes… It seems inevitable we’ll end up calling one of the two “Teegeeack”. :)
The Solar System May Have Passed through Dense Interstellar Cloud 2 Million Years Ago, Altering Earth’s Climate
https://www.bu.edu/articles/2024/the-solar-system-may-have-passed-through-interstellar-clouds/
If these clouds can do this to our solar system, how would it effect M dwarfs. What may be in these dense cold clouds? Large comets, rogue planets and water? Even oxygen, could whole atmospheres be replaced on arid worlds. What may be one of the final frontiers for understanding how worlds evolve over time and encounter intergalactic weather.