Let’s look at a second red dwarf planet in this small series on such, this one being Wolf 1069b. I want to mention it partly because of the prior post on K2-415b, where we had the good fortune to be dealing with a transiting world around an M-dwarf that should be useful in future atmospheric characterization efforts. Wolf 1069b, by contrast, was found by radial velocity methods, and I’m less interested in whether or not it’s in a ‘habitable’ orbit than in the system architecture here, which raises questions.
This work, recounted in a recent paper in Astronomy & Astrophysics, describes a planet that is not just Earth-sized, as is K2-415b, but roughly equivalent to Earth in mass, making a future search for biosignatures interesting once we have the capability of collecting photons directly from the planet. If the planet has an atmosphere, argue the authors of the paper, its surface temperature could reach 13 degrees Celsius, certainly a comfortable temperature for liquid water. A putative atmosphere would also shield the world from harmful radiation from the host star, although Wolf 1069 appears so far to be an unusually quiescent M-dwarf.
In fact, the lack of distorting surface activity on the star makes possible a high degree of accuracy in the radial velocity measurements here. The data, pulled in by one of the two CARMENES spectrographs, were taken by Diana Kossakowski (Max Planck Institute for Astronomy in Heidelberg), who is lead author of the paper on this work, and colleagues. The CARMENES instruments operate with the 3.5-metre telescope of the Calar Alto Observatory near Almería in southern Spain, and Kossakowski and team have been working the numbers on Wolf 1069 for the past four years.
Image: The figure shows measurements of the velocities at which the star Wolf 1069 moves towards or away from us by the mean. The measuring points were arranged in such a way that they depict the orbital period of the planet. This shows the tiny but significant variation in motion caused by the planet 1.3 times the mass of Earth orbiting in 15.56 days, and is illustrated by the gray line with the black dots. Credit: © D. Kossakowski et. al. from A&A 2023).
CARMENES is itself a research consortium (the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs program). The eleven German and Spanish institutions involved are focusing on Earth-like exoplanets near M-dwarfs, in other words, and I think we can expect the first doubtlessly controversial findings related to biomarkers will emerge on such worlds.
Wolf 1069b is on a 15.6 day orbit around an M-dwarf about 30 light years away in Cygnus. That distance is, of course, intriguing as we build the catalog for nearby worlds for future study of biomarkers or, one day, probes; the planet counts as the sixth-closest Earth mass world in a habitable zone orbit (the others are Proxima Centauri b, GJ 1061 d, Teegarden’s Star c, and GJ 1002 b and c). Keep in mind that only 1.5 percent of all the more than 5000 exoplanets yet detected have masses below two Earth masses – K2-415b, for all its interest, evidently weighs in at three.
Tidal lock is likely, though perhaps not a show-stopper for life, especially if the early indications of Wolf 1069’s low levels of activity are born out by future observation, and if an atmosphere is indeed present (without one, the authors estimate, the surface temperature would be 250 K, or -23 °C, as opposed to the + 13 °C mentioned above). So that interesting scenario of daylight (or night) that goes on forever emerges here.
Image: Simulated surface temperature map of Wolf 1069 b, assuming a modern Earth-like atmosphere. The map is centered at a point that always faces the central star. The temperatures are given in Kelvin (K). 273.15 K corresponds to 0 °C. Liquid water would be possible on the planet’s surface inside the red line. Credit: © Kossakowski et al. (2023) / MPIA.
But it’s something that Max Planck Institute for Astronomy scientist Remo Burn said that catches my eye:
“Our computer simulations show that about 5% of all evolving planetary systems around low-mass stars, such as Wolf 1069, end up with a single detectable planet. The simulations also reveal a stage of violent encounters with planetary embryos during the construction of the planetary system, leading to occasional catastrophic impacts,”
That’s a noteworthy thought, for such impacts could generate a planetary core that remains liquid today, resulting in a global magnetic field that would offer further shielding effects from stellar activity. The question would be whether Wolf 1069b really is alone, and on this the results are simply not in. What the researchers have been able to do is to exclude additional planets of Earth mass or more and orbital periods of less than 10 days. What they cannot do yet is rule out planets on wider orbits.
If alone around its star, Wolf 1069b is the only one of the six Earth-mass planets in habitable zones nearest to Earth that is found without an inner planet keeping it company. Note that the mass of Wolf 1069 is 0.167±0.011 solar masses. And now let’s turn to the paper:
This notion is supported by the works of Burn et al. (2021), Mulders et al. (2021), and Schlecker et al. (2021), where we expect a lower planet occurrence rate for stars with M* < 0.2 M? than for stars with 0.2 M? < M* < 0.5 M? for both the pebble and core accretion scenarios.
The authors run this out on a rather lengthy speculative thread:
Granted, these are theoretical predictions as more observation-based evidence is required to confirm this, and Wolf 1069b could still be accompanied by closer-in and outer planets. Nevertheless, the concept that only one planet survives is predicted by formation models if there were at least one giant impact at the late stage. This would enhance the chance of having a massive moon similar to the Earth and might also stir up the interior of the planet to prevent stratification and sustain a magnetic field (e.g., Jacobson et al. 2017). As remote as this appears, the search for exo-moons is no longer so far-fetched in recent times (e.g., Martínez-Rodríguez et al. 2019; Dobos et al. 2022).”
In the absence of data on these matters, speculation is welcome, but I can only imagine that when we get the right instrumentation online to make direct observations of planets like Wolf 1069b, we’re going to find more than our share of surprises. Whether or not an exo-moon hinting at an impact hinting at a magnetic field is one of them remains to be seen. A lot of ‘ifs’ creep into discussions of ‘habitable’ worlds. Would a tidally locked red dwarf planet look something like the speculation we see below?
Image: Artist’s conception of a rocky Earth-mass exoplanet like Wolf 1069 b orbiting a red dwarf star. If the planet had retained its atmosphere, chances are high that it would feature liquid water and habitable conditions over a wide area of its dayside. Credit: © NASA/Ames Research Center/Daniel Rutter.
The paper is Kossakowski et al., “The CARMENES search for exoplanets around M dwarfs Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby, very low-mass star,” Astronomy & Astrophysics Vol. 670, A84 (10 February 2023). Full text.
All is rosy so long as the water vapour does not rise above the vapour trap and gets horribly disassociated.
“K2-415b, for all its interest, evidently weighs in at three”
The evidence has it with a wide error bar 0.3-5, of which 2.2+ implies a planet of pure iron or heavier. So it’s no real evidence after all. (A superMercury at around twice Earth Mass might work.)
The problem this star has is exactly the problem W1069 doesn’t have: stellar noise.
It would be interesting to speculate how a technological species in a system with just one planet, their homeworld, would contemplate space travel. We have both the Moon, and the many planets with moons in our system. We had the understanding that these were places to go, and would provide interesting places to visit, with automated probes or crewed missions. But what of such systems with just one planet? There would be no history of thinking about other worlds to go to. No wanderers in their skies to investigate (other than comets). If they had a capability to reach space, there would be no places to explore. They wouldn’t know about exoplanets until their telescopes were very good, and they might not even have a concept for multiple planets in a system, if they think their system is the common type. Once they do detect exoplanets, they have no stepping stones to develop their technology to reach the stars, with no technical, scientific, and economically interesting neighbor worlds to reach before the far harder jump to the nearer star systems.
To my mind, they might be the archetypal worlds that might only use em communication as envisaged by SETI researchers. Spaceflight might be restricted to orbits of their homeworld, with a few further forays, but no reachable targets.
They could make use of the oberth maneuver quite well though around low mass stars to reach comets.
An interesting scenario! But I think organic factors still predominate. On a parallel Earth, I imagine wars would still have been fought with V-2 like rockets and nuclear weapons, so a push to near-orbital spaceflight would be inevitable. They would still launch satellites for spying, communications, weather; a few inhabitants would still be sent into space to test the conditions. The main distinction I imagine is that if there were only a few local asteroids – Bennu, Ryugu and such – then aggressive conflict to “claim” them for scarce space resources would more likely have commenced right away, which might have ended with some version of Project West Ford denying space to all comers. For all I know the war for the lunar south pole might still end that way anyway.
By contrast, picture the organic factors. The aliens might not survive in zero gee at all, or they might have evolved on a planet without an atmosphere and never seen space as very hostile. They might have evolved from a more migratory species whose philosophers couldn’t picture land ownership outside of a seasonal mating ritual, or which is too spontaneously violent for large governments to be able to organize deadly high-tech wars.
If a civilization gets to the right sort of asteroids, they might start colonizing some of them much as we might picture colonizing Mars, and from there one can imagine a slow march to the Oort cloud and beyond.
SETI theorists should spend more time imagining scenarios
that argue against finding extrasolar civilizations, such as this one. Space exploration may be a low priority among species who have nowhere to go in their vicinity. Such speculations may be of limited use when we do not know the frequency of single-planet systems due to the limitations of our detection technology. Still, these concepts can provide us some guidance as to how to engineer our search programs.
I’ve always felt uneasy with our assumption that other civilizations simply cannot wait to explore and settle space. That’s the way we tend to see ourselves, isn’t it, whether we are actually that way or not? Perhaps other species, even highly technically capable ones, simply see no need to aggressively explore the universe, or simply prefer not to do so until they have a very good reason.
Which of these attitudes (aggressive exploration vs fully exploiting and preserving local resources) is most common across multiple cultures will eventually influence the design, and eventual success, of our SETI programs. We simply do not have enough data now to predict which attitude is most likely among our neighbors, but an awareness of this dichotomy should at least be factored into our thinking on the subject.
My own personal opinion, (and that’s all it is, an opinion), is that the vast majority of technical civilizations simply will not bother to expend vast resources on a space program until they feel a pressing need for one. In fact, I have reason to believe the vast majority of the human race feel that way. I will grant you that we appear to be very motivated and skilled at space technology right now (early 21st century), but I also feel our own space programs are nowhere near as advanced as you might expect for a culture at our stage of technical development.
Remember Kubrick’s Space Odyssey? A constellation of elaborate human settlements on the moon and a fully functioning commercial orbital spaceport by 2001 seemed perfectly reasonable in the late 1960s, even before the Apollo landings. Here we are, a half century later, and we are nowhere near that level of penetration yet. We certainly have the technology, we just never generated the enthusiasm. I can think of other examples; we could construct and support cities on the ocean bottom but we never seemed to come up with a compelling reason to do so.
The “enthusiasm” of extrasolar species is a closed book to us, either in what they may feel, or in what they might have actually done. And we should also consider that many civilizations, after they have secured their
future by successfully establishing several distant colonies, may simply feel no need to continue expanding indefinitely. Once immortality is assured, dangerous and expensive travel seems less essential.
Our own history of exploration and colonization here on earth may simply be an artifact of our own retarded social development. Our culture is even today dominated by local rivalries and conflicts and competition. Species which have evolved social stability and planetary unity (which may be argued as essential for true expansion into the cosmos) will lack that motivation. Chronic resource shortages, another reason to leave home, may no longer be an issue to a truly advanced technology that is successful at conserving local materials, recycling them, or synthesizing them from local sources.
As for the desire to find and communicate with other civilizations? Perhaps they have already done so, and they have all the friends (or enemies) they need.
There is argument that some arrangements provide much easier space access and much more motivation than our own setting. But this is an interesting opposite case. Civilizations with easy access to space can hope to evade self-annihilation without correcting their imperfections (or maybe doing it only partially), by dispersing among the stars. Locked-in civilizations have no such option: their only way to survive is to make self-destruction impossible.
But these settings could turn out to be more special than “easier end”. Inhabitants of a single high-grav dense-atmosphere world would conceive and build their GPS about on the same stage as we have done, just using beamride/nuclear rockets and cloud launch platforms. Much easier than going straight to the stars. They’ll discover exoplanets about the same time – there would be debris from giant impacts, implying that multiple-planet systems are possible and provoking interest to study other stars. And then, there is the gravity well of central star, much easier to use for Oberth maneuvers because of lower heat loads, and much closer gravlens, tens of AUs instead of our 550.
More, are we closer to the “easy-access”, or to the “locked-in” end of the spectrum? To put eggs out of a single basket thoroughly, inhabitants of Wolf-1069 b would have to go to the stars or to build self-sufficient vacuum habitats almost like we have to. Mars-like worlds offer little relief since timescale of full terraformation is much bigger than that of self-destruction in technological explosion. The only factor that makes dissemination qualitatively easier is an another unconditionally habitable planet in the same system, and these are likely more frequent than single-planet systems.
I’m lucky I wasn’t drinking something messy when I read that 30 light-years counted as the “sixth-closest Earth mass world in a habitable zone orbit”. Those exoplanets have been creeping up on us! And this data about Earth-sized worlds and planets in most orbits is still very incomplete…
There aren’t so many times where I feel like I’m living in the promised sci-fi world of the 21st century. Cancer still kills people, kids still try to use mechanical pencils even though they don’t work, flu still reigns unchecked, air conditioners are still noisy contraptions, cars still need new tires. But this … astronomers have found something new under the suns.
If the planetary surface area under the host star is able to permit liquid water, will not evaporation and atmospheric currents carry the water to other regions where it may be deposited as a solid, which over time may deplete the liquid water?
Searching for Alien Life: Can JWST Detect Biosignatures on Exoplanets?
– Architecture can make a difference.
I was just reading this and then starting reading about this one.
Do we need a 5th class? the sole Planet System?
An interesting look at the types of solar systems
It looks like the red circle extends 55 degrees in any direction from the subsolar point. Plants grow slowly at slightly above freezing. Say 45 degrees from subsolar for faster growth.
On earth, 29% of both hemisphere is within 45 degrees of the pole. 1- sin 45 = 1 – .7071 = .293. One hemisphere is forever dark, so that leaves 15% of the surface of the planet.
Alaska is not hot, yet abundant sunshine in the short summer growing season sees many plants, plus billions of mosquitoes.
Earth feeds 8 billion people, so planet 1069b could feed 1.2 billion, all else being equal. I’d cut that in half due to the shortage of blue light for photosynthesis – still enough to support a civilization. [What do I know about biology?] For how long could the ecology sustain that number of people or ETs? That’s a good for both planets.
I wanted to see what this looks like in terms of the usually quoted equilibrium temperature… Using a formula found on Wikipedia: Tp = (3158 K) (0.1813 Rsun /2* 0.0672 au * Rsun/214.94 au)^0.5 * (1-albedo)^0.25, which comes out to 250 K if albedo = 0, or 229 K if albedo is 0.3. Earth’s equilibrium temperature is (5772 K) (1 Rsun / 2*1 au * Rsun/214.94 au)^0.5 * (1-0.3)^0.25 = 255 K.
The average temperature on Earth is 13 C = 286 K, which is the same as the maximum for the sun-facing side here. From this model it looks like stopping the rotation of the planet really doesn’t increase the temperature of the day side all that much – it’s comparable to painting it black.
A planetary magnetic field needs more than just a liquid core. It needs a fast rotation like Earth’s because charged particles have to move and circles to have a magnetic field like a wire with an electric current wrapped around a nail in circles which is an electromagnet; Moving electrons emit EMR. A tidally locked exoplanet can’t have a magnetic field so there is more atmospheric stripping by the solar wind.
The authors argue that a large moon could provide enough tidal effect to produce the magnetic field:
“…the concept that only one planet survives is predicted by formation models if there were at least one giant impact at the late stage. This would enhance the chance of having a massive moon similar to the Earth and might also stir up the interior of the planet to prevent stratification and sustain a magnetic field.”
I found this paper which dives into the topic: https://arxiv.org/pdf/1204.0275.pdf It seems like the main contributor to the magnetic field is convection as the core loses heat. Rotation does have some effect on atmosphere retention (see figure 6 and 7). A key piece of data factoring in is whether Venus had an Earth-like magnetic field a billion years ago; an experiment was proposed to study this. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL082725
Venus is the perfect example of a planet that has convection in a liquid core, but no magnetic field which is why a fast rotation is necessary. It’s not just convection that gives the Earth it’s magnetic field, but the circular movement of the liquid core caused by Earth’s rotation. Also the Hill radius and Roche limit make it impossible for a tidally locked Earth sized exoplanet to have a Moon. A Moon gets ejected from that two body system, is broken into pieces or it can’t ever form.
Recall our Earth’s fast rotation is from a collision with a Mars sized body called Theia which gave Earth a lot of angular momentum and fast rotation. Theia was destroyed, but it blasted Earth’s entire mantle off into space which circled the Earth in an orbit and became our Moon. The iron core of Theia went into our Earth giving it a larger iron core. This isn’t speculation, but fact proven by the sea shells of Scallops which make one line every day of the year, but the Scallops of the past have more lines on them since the Earth was spinning on it’s axis faster in the past so there were more days in a year. The shorelines were much wider and the tides moved much further inland since the Moon was closer and the gravity and tidal forces stronger. The Abyss of Time, Lyle. Also the entire crust of the Moon is made of Anorthosite or plageoclase feldspar down to forty miles which is the same chemical composition of Earth’s mantle, a fact brought to us by our Apollo astronauts and Moon rocks.
Venus of course rotates backwards every 243 days, a slow rotation and too slow for a magnetic field. It is tidally locked by the Sun.
Slightly off topic could we terraform tidally locked worlds as are more than likely around M dwarfs. Perhaps load the atmosphere with CFC’s or greenhouse gases that don’t freeze out.