We rarely talk about Teegarden’s Star when mentioning interesting objects near the Solar System, probably because the star was only discovered in 2003 and until now had not been known to host planets. Today we learn, however, that an international team led by the University of Göttingen has found two planets close to Earth mass in what it considers to be the habitable zone around the tiny star. Interestingly, from where the system is located, any local astronomers would be able to see the planets of our Solar System in transit across the face of the Sun, about which more in a moment.
One of the reasons that this comparatively nearby star has been so late to be discovered is its size. We are dealing with an M-class red dwarf, this one in the constellation Aries, and no more than 12.5 light years from us. It took three years of patient radial velocity monitoring to track down planets around a star that is only about 2700 degrees Celsius in temperature, and fully 10 times lighter than the Sun. What we now have are two planet candidates, each with a minimum mass 1.1 times that of Earth, with orbital periods of 4.91 and 11.4 days respectively.
These are, according to the paper, “…the first Earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities.”
Because no transits have been detected, the scientists have no information on planetary radii, and therefore estimated them based on various possible compositions, from rocky to gaseous mini-Neptune, finding that the resulting radii differ by a factor of about three. The other stellar and planetary parameters were plugged into the Earth Similarity Index (ESI), which compares key parameters to those of Earth. If these worlds are not mini-Neptunes, we get this (from the paper):
Except for the case of a mini-Neptune composition, the two planets have a high ESI. For a potentially rocky composition, the ESI value is 0.94 and 0.8 for planets b and c, respectively. This makes Teegarden’s Star b the planet with currently the highest ESI value. However, the ESI is only an estimate, and different weighting of the parameters may lead to changing ESIs. This ESI definition, for example, does not take into account the stellar spectral energy distribution and the resulting planetary atmospheric composition, which very likely have an effect on habitability.
So we push at the boundaries of what we still don’t know. Lead author Matthias Zechmeister (University of Göttingen) noted the resemblance between these two worlds and the inner planets of our Solar System, saying “They are only slightly heavier than Earth and are located in the so-called habitable zone, where water can be present in liquid form.” I asked Dr. Zechmeister to amplify on the habitability zone finding, to which he replied:
You may have noted that PHL (http://phl.upr.edu/press-releases/pr_draft_tee4321) ranks Teegarden b now as the exoplanet most similar to Earth. The conditions are good for liquid water on the surface, given a similar insolation and mass as Earth’s. Still, we cannot be sure to 100%. We have measured “only” the mass (which is a minimum mass, but true masses are statistically only ~16% higher). So we do not know the true chemical composition, though a rocky composition is probable (see Fig. 12 in the paper for other compositions).
Dr. Zechmeister also made note of the fact that Teegarden’s Star is about 8 billion years old, roughly twice the age of the Sun, allowing plenty of time for interesting things to develop if life ever took hold there. And he raised a caution re the habitability issue, noting that the diminutive star is what he refers to as ‘an extreme host,’ a type of star about which we still have a great deal to learn.
So small is Teegarden’s Star that it is not far above the upper size limit for brown dwarfs, often considered to be somewhere between 60 and 90 Jupiter masses, and at magnitude 15, it demands a large telescope to see it at all. In fact, it was actually discovered in 2003 via stored data in the Near-Earth Asteroid Tracking (NEAT) program, and had been logged in our data earlier, turning up on photographic plates from the Palomar Sky Survey taken in 1951.
Image: Comparison habitable zone in Teff [effective temperaeture] – HZ diagram. Credit: C. Harman.
Now ponder this: Radial velocity detections have produced more than 800 exoplanets, but few have been found around old, cool M-dwarfs. In fact, we have only two other planet hosts with effective temperatures cooler than 3,000 K, and one of these is Proxima Centauri, while the other is TRAPPIST-1, around which fully seven transiting planets are known to exist. The authors of the paper on the Teegarden’s Star work consider the lack of planet detections around very late-type stars the result of observational bias owing to the faintness of the objects at visible wavelengths.
From the paper:
Both planets have a minimum mass close to one Earth mass, and given a rocky, partially iron, or water composition, they are expected to have Earth-like radii. Additionally, they are close to or within the conservative HZ, or in other words, they are potentially habitable. Our age estimate of 8 Gyr implies that these planets are about twice as old as the solar system. Interestingly, our solar system currently is within the transit zone as seen from Teegarden’s Star. For any potential Teegardians, the Earth will be observable as a transiting planet from 2044 until 2496.
A later note from co-author Guillem Anglada-Escudé, the discoverer of Proxima Centauri b, unpacks this further. The transit that would be visible from this system in 2044 would have occurred in our Solar System in 2032, factoring in the 12 year light travel time. There have been SETI discussions regarding the possibility of conducting communication attempts of stars whose planets would see our own world in transit around the Sun, so any such attempt would need to take place in 2032 or later, with the earliest potential response expected around 2056.
Image: Top 19 potentially habitable exoplanets, sorted by distance from Earth. Credit: A. Mendez (PHL).
The team behind this work used data from CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs), an effort using two separate spectrographs located at the 3.5m telescope at the Calar Alto Observatory in Almeria, Spain. The goal of the project, conducted by a consortium of German and Spanish institutions, is to carry out a survey of approximately 300 late-type main-sequence stars with the goal of detecting low-mass planets in their habitable zones.
We have not, in other words, heard the last from CARMENES.
The paper is Zechmeister et al. “The CARMENES search for exoplanets around M dwarfs – Two temperate Earth-mass planet candidates around Teegarden’s Star,” accepted at Astronomy & Astrophysics 2019 (abstract).
I was utterly stunned by this news! TWO HUGE QUESTIONS! One, if the two spectrographs on the Calar Alto telescope were moved to either one of the Keck telescopes or one of the VLT telescopes, could the extra light gathering power of these telescopes allow viable radial velocity measurements of the TRAPPIST-1 planets to be taken? Two, have the TRAPPIST and SPECULOOS telescopes made enough observations of Teegardens Star to ELIMINATE ANY POSSIBILITY of small Mars-like planets with masses too low to be detected by CARMENES transiting INTERIOR to Teegarden’s Star b? THIS IS CRUCIAL, because the the Spitzer Space Telescope is due to be de=commissioned in January. We need to know VERY QUICKLY whether any such planets exist for Spitzer to have any shot at observing them. Finally, Abel Mendez DOES NOT PUT TRAPPIST-1d in the conservative habitable zone, and therefore Teegarden’s Star b should not be considered in it either.
How “quiet” is the red dwarf star in question? I believe we have two types of red dwarf stars, one with very active solar flares and other which is relatively calm…
The question about habitability is very complex one…An old system/planet like that could have problem with water presence I think…
Oops. TRAPPIST-1d is now listed IN the conservative HZ. Dr Mendez has completely re-configured the PHL website from when I saw it last. Andrew Le Page: Any reason why TRAPPIST-1d is BACK in the conservative HZ?
Well, I don’t put much stock into the Earth Similarity Index (ESI) used by PHL to rate potential habitability exoplanets. That being said, I still hold to my original assessment from two years ago (link below) and consider TRAPPIST-1d to have so-so chances of being considered potentially habitable since it seems to orbit right near some definitions of the inner edge of the HZ for synchronous rotators. Planets e and, to a lesser extent, f have better habitability prospects in my estimation.
https://www.drewexmachina.com/2017/02/25/habitable-planet-reality-check-the-seven-planets-of-trappist-1/
Not so fast! Due to very complicated tidal interactions with the inner and outer TRAPPIST-1 planets, the middle planets may NOT be tidally locked ALL OF THE TIME! ArXiv: 1905.11419 “The Chaotic Nature of TRAPPIST-1 Planetary Spin Rates. by Vinson, a., Tamayo, D & Hansen, B.
If this proves to be the case, then the habitability prospects for TRAPPIST-1d would be impacted further compromising PHL’s overly rosey assessment.
Alas, poor Westeros, trapped on the night side of a now tidally locked TRAPPIST-1e for the next few thousand years! Levity aside, this to me appears to be the LEAST contrived “hard science” scenario for the “Game Of Thrones” continent’s fate.
Article illegible due to bad formatting (at least in Firefox).
Wow, you’re right. Seems to be fine in Chrome but the video distorts Firefox beyond redemption. I just pulled the video out.
Working fine for me in Forefox
Good to hear that, Laintal. I had to remove the video, which apparently wasn’t automatically re-sizing in Firefox as it did in Chrome. Whatever the cause, the problem disappeared after that.
Teagarden’s Star shall be receiving a radio message sent from Earth one decade ago via Arecibo in just a few years time now…
https://centauri-dreams.org/2009/11/18/%e2%80%9crubisco-stars%e2%80%9d-and-the-riddle-of-life/
https://centauri-dreams.org/2009/11/19/rubisco-stars-part-ii/
We will need a lot more information about these two candidates. I usually like to read The Habitable Planet Reality Check by Andrew LePage on the DrewexMachina website once some time has gone by. He does a very good job analyzing potential habitable planet candidates (and does great articles like Paul) :).
Thank you, Gary. And yes, Drew is a wonderful source for deep dives into questions of habitability. I’ve learned a lot from his work. Those not familiar with his site should check it out at: https://www.drewexmachina.com/blog/
Hi Paul
Well this fits the recent study that computes there’s about 3 planets on average for every red dwarf star. What an era we live in, to have such a wealth of (probable) planets known around other stars, yet so tantalisingly out of reach. Based on that recent study on the carbon monoxide “uninhabitable zone” these planets could be chokingly rich in that toxic oxide. But, like all things about red dwarf habitability, we’re trying to span an abyss of ignorance with a narrow plank of inference.
If red dwarf’s flares strip an atmosphere, could it be reconstituted by later cometary impacts and/or geological processes after the red dwarf enters quiescence? And would variant biologies be better adapted to panspermia?
Do we have any data on the metallicity of Teegarden’s star? I ask because it is relatively old, so it may not have “enough” of them. “Life” as we know it requires “astronomers’ metals” (CHNOPS at least), and “real metals” as high up the periodic table as Zinc.
Okay, I checked this out myself… learned some stuff too… According to Wikipedia, Teegarden’s star has metallicity of -0.55 dex, which is the exponent of the ratio of its metallicity (Fe/H) to that of Sol, so the value is 0.28 that of Sol. Sol has metallicity Z = 0.0122 (mass of elements > He as a proportion of total mass), so TS has Z = 0.00344. Is this high enough to provide the resources for life? I realize that this question probes well beyond our knowledge, but I suspect that the answer is ‘no’.
djlactin,
Nothing authoritative or definitive here, but just to get the ball rolling.
Consider that the star was formed earlier than the sun and that the medium from it formed was likely less enriched in “metals”. Now, consider the fact that the star has planets, two of which are detectable and about the mass of earth. Volatiles in the temperate region would be eroded away by normal and variational flux, but some dependence on magnetosphere.
Now there must be some connection between the medium and the stellar content, but over billions of years there could be manufacture of “metals’. A red dwarf, the dominant process by far would be hydrogen into helium, but the metallicity might even be one of the markers of age.
But the fact that you have two planets in the temperate zone not made out of fluff is an argument for sufficient chemical content for life: presence of C, N, O, H, P, … sitting atop silicon and iron. How things aggregate in a small circumstellar disk near a red dwarf might be the issue or what to examine.
Additionally, a couple of exoplanets detected were in orbit about very ancient stars, dating back to eleven billion years. I don’t know about life viability, but despite the poor metalicity of those days, there was something to nucleate around…
To your first question, CARMENES could be installed in a VLT BUT it would require specially designed adaptive optics or most of the extra light from the apperture would be lost (has to do with a technical concept called ettandue for light beams). ESPRESSO, similar to the visual arm of CARMENES is a much bigger instrument.On the other hand, u can have an Echelle the size of a shoe box for a 0.5m semipro telescope.
Concerning SPITZER, unfortunately we tried and got rejected. Argument was it could be done from the ground, but that is bollocks as we all know how much easier and clear SPITZER data would have been. I also suspect politics as we were not a very USA team. Hopefully someone with a more suitable affiliation tries before it is too late. Teegarden’s star is in the ecliptic, meaning TESS cannot do it… If these things indeed transit, this would be huge for JWST prospects of characterising atmospheres
Disclosure : I am a positively biased co-author in the paper, so pretty excited and a bit frustrated as well
Dr Escude: The reason I mentioned Spitzer at all is, in case the TRAPPIST-SPECULOOS consortium fails to turn up any 0.4-0.5 Earth radii planets orbiting interior to Teegarden’s Star b, since(correct me if I am wrong)the TESS target catalog does not contain Teegarden’s Star because it is not bright enough, the only telescopes that can detect transits of planets <0.4 Earth radii would be Spitzer and Hubble. Also, the recently published(by Heller, Hippke et al)Transit Least Squares method for teasing out transits that do not meet the threshold requirements of conventional methods work best for telescopes like Spitzer and Hubble. The reason I feel that detecting these transits is so important is you can then place a stringent upper limit on the mass of Teegarden's Star b by using TTV's of transiting planets interior to it, should any indeed exist. Finally, this hopefully could be an impetus for ESA or some other non-USA institution for taking over the operation of Spitzer in January and operate it at least until JWST comes online, or until Spitzer runs out of fuel, whichever comes first. And now for a bit of wild speculation. Are you aware of any attempts prior to your discovery by SETI radio telescopes to monitor Teegarden's Star for non-natural radio or laser emissions? I am very intrigued by the virtual lack of signifigant flaring of this star. A Kardeshev type II civilization may have found a way to dampen such flares which would otherwise exist.
I tried a quick search with the keywords Teegarden and SETI and came up with nothing definite. I also searched here:
https://technosearch.seti.org/
This page may be useful in general:
http://www.solstation.com/stars/so025300.htm
Also try “The Breakthrough Listen Search for Intelligent life: Observations of 1327 Nearby Stars over 1.1-3.46GHz.” Hopefully this is arranged in a “nearest to furthest’ format, otherwise this may take a while.
https://arxiv.org/abs/1709.03491
The Breakthrough Listen Search for Intelligent Life: 1.1-1.9 GHz observations of 692 Nearby Stars
J. Emilio Enriquez, Andrew Siemion, Griffin Foster, Vishal Gajjar, Greg Hellbourg, Jack Hickish, Howard Isaacson, Danny C. Price, Steve Croft, David DeBoer, Matt Lebofsky, David MacMahon, Dan Werthimer
(Submitted on 11 Sep 2017 (v1), last revised 20 Apr 2018 (this version, v2))
We report on a search for engineered signals from a sample of 692 nearby stars using the Robert C. Byrd Green Bank Telescope, undertaken as part of the Breakthrough Listen Initiative search for extraterrestrial intelligence.
Observations were made over 1.1? 1.9 GHz (L band), with three sets of five-minute observations of the 692 primary targets, interspersed with five-minute observations of secondary targets. By comparing the “ON” and “OFF” observations we are able to identify terrestrial interference and place limits on the presence of engineered signals from putative extraterrestrial civilizations inhabiting the environs of the target stars.
During the analysis, eleven events passed our thresholding algorithm, but a detailed analysis of their properties indicates they are consistent with known examples of anthropogenic radio frequency interference.
We conclude that, at the time of our observations, none of the observed systems host high-duty-cycle radio transmitters emitting between 1.1 and 1.9 GHz with an Equivalent Isotropic Radiated Power of ?10 13 W, which is readily achievable by our own civilization.
Our results suggest that fewer than ? 0.1% of the stellar systems within 50 pc possess the type of transmitters searched in this survey.
Comments: ApJ. 13 pages, 7 figures, 4 tables. This version has a typo correction to Eq. (4)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
DOI: 10.3847/1538-4357/aa8d1b
Cite as: arXiv:1709.03491 [astro-ph.EP]
(or arXiv:1709.03491v2 [astro-ph.EP] for this version)
Submission history
From: J. Emilio Enriquez [view email]
[v1] Mon, 11 Sep 2017 17:53:04 UTC (706 KB)
[v2] Fri, 20 Apr 2018 02:21:55 UTC (764 KB)
https://arxiv.org/pdf/1709.03491.pdf
https://iopscience.iop.org/article/10.3847/1538-4357/aa8d1b/pdf
Gee, with all the comments mentioning my name, it is no wonder my ears were burning all day yesterday. Fortunately I was able to rearrange my schedule yesterday and was able to get a “Habitable Planet Reality Check” prepared about these new find orbiting Teegarden’s Star (my first published “Reality Check” in 15 months). Enjoy!
https://www.drewexmachina.com/2019/06/19/habitable-planet-reality-check-the-earth-size-planets-of-teegardens-star/
Thanks, I’m glad you mentioned the history of Teagarden’s Star: it may be quiet and relatively un-flare-y now, in its old age, but it probably wasn’t quiet for a good long period before the present–long enough that it’s difficult to imagine it not having been detrimental to any atmospheres on these planets, would you say?
Yes a great update Andrew
This, of course, is very exciting news about 2 nearby planets with habitability potential. But since the habitability matter lurks in the background, it might be interesting to have a few articles about the habitability zone concept.
I suspect that when the concept was introduced, the sun and Earth as reference points circa year 2000 evolution and solar flux had
much to do with the model. ( “We are here, therefore factors associated with our existence have model priority…”). This also tends to equate spacing at a 400 kelvin radius as a standoff point from a G2 main sequence star. But the celestial sphere has the entire main sequence and outliers, plus planets have varied albedos/reflectances, thermal inertias and internal heats. Over stellar time histories, their output tends to vary, including feastures such as flares. Stellar fluxes with surface temperature radiate higher or lower in the UV or IR despite the same standoff blackbody temperature. Heat transport in atmospheres and oceansdepend on circulation patterns established by both celestial mechanicsand geology…
An expert or a committee of such could elaborate on all these matters. They would probably protest that I haven’t scratched the surface.
And yet I’m not even sure that the qualifications above necessarily rule against the establishment of habitability or make it any more difficult.
If our own geologic history is considered, we have definitely run a gauntlet.
In the presence of microscopic life, the atmosphere, oceans and minerals of a world could very well be altered as much as the Earth’s over time. Some of it is in response to cataclysmic events – which would normally be interpreted as inhabitability for a time.
Whether M dwarf flare events would wipe out the prospects of life…?
At face value outbursts like that would make things difficult – if a world looked like ours does now early on. But what if they had many more volatiles? How much water would they have had to start out with to look as hydrated as we do now? And in our case, we are gaging things based on an object (Earht) that is presumed to have survived a collision with a Mars sized object which resulted in the formation of 2000 mile wide desiccated moon.
One area that may be done from this distance is what the cometary activity is and how large a resevoir exist at this time. This could give at least an idea of how much viotales still exist on these planets. What chemical and molecular compounds might be detectable from radio to the xray spectrums around Teegarden.
What you call for wdk is excellent. With all the variables in play the subject of what exactly the limits are for any type of life to exist on a planet is quite complex. Books could be written on the subject …
I would be interested to hear how transfer orbits between these two planets could be done. Would it take a lot of energy because the planets are deep in the gravity well of their sun? How would it compare to Jupiters system or as complicated as reaching Mercury from Earth.
Since these planets are so close to each other, some 1.76 million miles at closest approach, 7 times the earth moon distance, tidal influences should be high. Each planets mass is close to 100 times that of our moon and this could easily dislodge the tidal locking of planet b. Correct me but opposition should occur every 8.5 days, so could be very interesting geologic effects over 8 billion years. These two planets have similar orbits to Trappist 1’s d and e orbits for Teegarden’s b and Trappist 1’s f and g for c. Hopefully these are close enough for atmosheric composition and geologic mapping in the next decade with the giant telescopes coming online! These types of planetary systems are the most common in our universe!
Heads up, they may also have the most alien life forms and civilizations compared to ours!!! ;-{?
Michael Fidler,
Per your request for information, tried my hand at calculating some
orbital velocities in the Teegarden system. Used data from Andrew Page website. ( My first visit. Very helpful and informative on states of exoplanet affairs. Appreciate hearing about this site).
To use some abbreviation. The earth goes around the sun at close to 30 km/sec. So with the lowered Teegarden mass of the primary 0.089 and the the planetary radii in hundredths of AUs ( 0.0252 and 0.0443), I got velocities for B and C of 1.8793 and 1.4174 of the terrestrial value.
If you wanted to get on a Hohmann path from B to C, disregarding the planetary gravity wells, the delta velocity would be about 0.2485 or close to 7.5 km sec. I think heading off to Mars, based on v at infinity
heading away from earth is about 2 kilometers per second.
So, in summary: Yes, commuting between the two habitable planets would be relatively expensive as compared to Earth and Mars.
But perhaps there will be commensurate rewards.
Also, it’s a modest cost compared to getting to the system in the first place.
… The thought crosses my mind: instead of having chemical rockets do this job, maybe, it could be done solar electric? Well, a spiral path of
a few revolutions wouldn’t be so bad… But, looking at my LED light bulbs, gauged for indoor lighting ( 2700 K) vs. solar (5800), I have to wonder how efficient solar panels are at that spectral peak?
@wdk – I did the same calculations with a different motive and came up with the same answers so confirming that your math is correct. My interest was in determining how much harder would it be to leave Teagarden’s Star from a circumstellar orbit at C’s orbital radius of 0.0443 AU. The answer is dependent on orbital speed and would therefore be 41.74% higher than solar escape velocity from a 1 AU solar orbit. Not necessarily a deal breaker, but it is harder to escape from the habitable zone of dim stars.
Thanks wdk and Joy for your comments. What has me so interested is just how difficult it is to travel in these systems and how common they are. Miniature red dwarf planetary systems should be 20 or more common then solar type stars. So now if life is as adaptable as it seems to be the carbon monoxide and carbon dioxide forecast to develop on red dwarf planets may have been broken down by carbon oxide eaters life forms. On earth oxygen eaters have been only around for half a billion years. I would think nature could work out a way for life to develop with 20 times the habitable planets in these liquid water zones. Plus no one has advanced just how much activity with comets in miniature solar systems might keep viotales common.
So would trips from b to c be a common development in these type of habitable planets if advanced life develop on one of them? These may be the best examples of what is the most common planet formations. Maybe we can observe the infrastructure that has developed from them, that may still exist. Dyson hunting anyone?
The carbon monoxide abundance issue – I’ve been slow on the take with this. Probably others are as well, so I hope someone will pick this up and give a review. But granted, assuming an
overabundance vs. earth’s environment of carbon monoxide, what does this spell for life forming on a a world?
Well, from my understanding of CO in geochemistry, it is an unstable quantity, just like ammonia, probably more so. You generate in hydrocarbon exhaust and it converts rapidly to CO2 or combines with other gases to rovide hydrocarbon or carbon chemistry. Other planets in the solar system it becomes detectable. In the case of Jupiter, it appears to be out of balance with temperature possibly due to updrafts or convection. So, we have carbonaceous cliffs here as well as organic jungles. Are they impossible to obtain around a dwarf star? Well, there might be alot of CO2 in the atmosphere originally, just like with Venus or Mars. But the earth might have had a lot too prior to the bacteria activity that produced free oxygen.
CO sounds like it might be a good canidate for early life’s development. “Carbon monoxide is a nutrient for methanogenic archaea, which reduce it to methane using hydrogen. Extremophile micro-organisms can, thus, utilize CO in such locations as the thermal vents of volcanoes.”
For exoplanet stories, I eagerly read Centauri Dreams, but my first stop for extrasolar planet news has long been Extrasolar Visions forum ( http://solar-flux.forumandco.com/index.htm ) . Lately, the forum has been down. Does anyone know what happened to it? Have the forum members have reconvened somewhere else? The regulars there were very well-informed and I miss their commentary. Any info on the Extrasolar Visions forum would be greatly appreciated!
Here is the new link of the Extrasolar Visions II:
http://solar-flux.forumotion.com
Hooray! Thank you very much!
And now the THIRD planetary system orbiting an ultra cool dwarf(the definition of an ultra cool dwarf is main sequence spectral type M6 or later, so Proxima Centauri just doesn’t quite make it in). TESS has just had two planets validated orbiting the ultra cool dwarf star LP 791-18(M6V, Radius: 0.17Rsun, Temperature: 2960K, Distance: 26.493 parsecs, or ~80 light years. Planet b: 1.1 Earth radius with an orbital period of 0.95 days. Planet c: 2.3 Earth radius with an orbital period of 5 days. No other planets were detected in TESS’s 22 day observation run, and thus apparently no transiting planets in the habitable zone around this star, although it should OBVIOUSLY be a PRIME TARGET for Rene Heller and Michael Hippke to run a Transit Least Squares diagnostic on, just to be sure! I do not know if this star is observable by CARMENES or not, or whether there is enough light coming from the star due to its much greater distance from Earth than Teegarden’s Star’s distance from Earth to search for non-transiting planets in the HZ should Transit Least Squares turn up nothing.
CO2 and fungi, may be the ancient panspermia.
4 THINGS TO KNOW ABOUT FUNGI ‘CLIMATE WARRIORS’
https://www.futurity.org/mycorrhizal-fungi-forests-1822492-2/
How fungi could save the world.
https://www.weforum.org/agenda/2018/08/10-surprising-facts-about-fungi/
Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs
Jennifer G. Winters, Amber A. Medina, Jonathan M. Irwin, David Charbonneau, Nicola Astudillo-Defru, Elliott P. Horch, Jason D. Eastman, Eliot Vrijmoet, Todd J. Henry, Hannah Diamond-Lowe, Elaine Winston, Xavier Bonfils, George R. Ricker, Roland Vanderspek, David W. Latham, Sara Seager, Joshua N. Winn, Jon M. Jenkins, St’ephane Udry, Dr. Joseph D. Twicken, Johanna K. Teske, Peter Tenenbaum, Francesco Pepe, Felipe Murgas, Philip S. Muirhead, Jessica Mink, Christophe Lovis, Alan M. Levine, S’ebastien L’epine, Wei-Chun Jao, Christopher E. Henze, G’abor Fur’esz, Thierry Forveille, Pedro Figueira, Gilbert A. Esquerdo, Courtney D. Dressing, Rodrigo F. D’iaz, Xavier Delfosse, Chris J. Burke, Franois Bouchy, Perry Berlind, Jose-Manuel Almenara
(Submitted on 24 Jun 2019)
We present the discovery from TESS data of LTT 1445Ab. At a distance of 6.9 parsecs, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use follow-up observations from MEarth and the centroid offset analysis in the TESS data validation report to determine that the planet transits the primary star in the system. The planet has a radius 1.35 R_Earth, an orbital period of 5.35882 days, and an equilibrium temperature of 428 K. With radial velocities from HARPS, we place a three-sigma upper mass limit of 8.4 M_Earth on the candidate. The planet provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. The presence of stellar companions of similar spectral type may facilitate such ground-based studies by providing a calibration source to remove telluric variations. In addition, we present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicates a moderate amount of variability, in agreement with the observed low-level, short-term variability in the TESS light curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system raises the possibility that the entire system is co-planar, which implies that the system may have formed from the early fragmentation of an individual protostellar core.
https://arxiv.org/pdf/1906.10147.pdf