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Ross 508 b: What We Can Learn from a Red Dwarf Super-Earth

The discovery of a super-Earth around the M-dwarf Ross 508 gives us an interesting new world close to, if not sometimes within, the inner edge of the star’s habitable zone. This is noteworthy not simply because of the inherent interest of the planet, but because the method used to detect it was Doppler spectroscopy. In other words, radial velocity methods in which we study shifts in the spectrum of the star are here being applied to a late M-dwarf that emits most of its energies in the near-infrared (NIR).

I usually think about transits in relation to M-dwarf planets, because our space-based observatories, from CoRoT to Kepler and now TESS, have demonstrated the power of these techniques in finding exoplanets. M-dwarfs are made to order for transits because they’re small enough to offer deep transits – the signature of the planet in the star’s lightcurve is more pronounced than a transit across a larger star.

From a radial velocity perspective, planets in an M-dwarf habitable zone orbit the star closely, making for a strong RV signal if we can detect it. But there are limitations to both methods: Transit searches have clustered around younger red dwarfs that are relatively more massive. In terms of radial velocity, most exoplanet surveys have employed optical CCDs, whereas older, more evolved M-dwarfs are brighter in the near-infrared (NIR). From an exoplanet perspective, then, it can be said that cool late M-dwarfs remain largely unexplored terrain, a situation that is now being addressed.

What is needed for this kind of work is a spectrograph specifically designed for NIR wavelengths, and in fact NIR spectrographs have begun to appear, some of which involve projects we’ve looked at here, as for example CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs). Other such projects, like SPIROU (SPectropolarimetre InfraROUge) and HPF (Habitable Planet Finder) also employ NIR spectrographs.

The most famous of the M-dwarf planets is, of course, Proxima Centauri b, found by the team led by Guillem Anglada-Escudé using visible light spectroscopy, but M-dwarfs with temperatures below the roughly 3000 K of Proxima Centauri, which are considered late-type M-dwarfs, have not been systematically searched for planets.

Consider this: Seen from 30 light years out, the Sun is a 5th magnitude object in visible light, but a 3rd magnitude target in infrared. A late-type red dwarf comes in at around 19th magnitude in visible light, but brightens to 11th magnitude in the infrared. We’ve found dozens of exoplanets around stars with effective temperature higher than 3,000 K, but only a handful around cooler M-dwarfs. The authors of the discovery paper on Ross 508 b are not exaggerating when they describe the detection of planets around such stars using high-precision radial velocity methods as “a frontier in exoplanet exploration.” Their paper serves as a helpful introduction to NIR spectroscopy.

The team, led by Hiroki Harakawa (NAOJ Subaru Telescope, Hawaii), reports on the Ross 508 work as the beginning of a campaign exploring low-temperature stars with the Subaru Telescope IRD (InfraRed Doppler) instrument, which the Astrobiology Center of Japan, where it was developed, describes as the first high-precision infrared spectrograph for 8-meter class telescopes. The observing program now underway is the IRD Subaru Strategic Program (IRD-SSP), which began in 2019 and scans late-type M-dwarfs. Stable red dwarfs with low surface activity are the targets.

Radial velocity is the detection of stellar wobbles that can be indicated in several ways, making finding planets a matter of excluding false-positives as much as locating candidates. Because M-dwarfs are prone to violent flare activity, they’re problematic thanks to the changes in surface brightness they produce. A false planetary signature like this has to be extracted and then subtracted from the signature of a possible planet. Ross 508 b holds up to the scrutiny, indicating a minimum mass about four times that of Earth at an average distance of 0.05 AU from the star.

There are indications that the planet’s orbit is elliptical, with an orbital period of about 11 days, part of which may include crossing into and back out of the habitable zone. An interesting consequence of studying late-type M-dwarfs is that their presumed lower levels of flare activity may offer a planetary environment more conducive for life than their younger cousins, with a surface less frequently bathed in flare-induced radiation. I hasten to add that this is a tentative conclusion still the subject of active study.

In any case, a planet like Ross 508 b may well turn out to be a target for atmospheric analysis once we’re able to image it directly, probably with the coming generation of 30-meter class telescopes. Transits are unlikely here, so we’re reliant on imaging rather than transmission spectroscopy, which analyzes planetary atmospheres by studying the star’s light as it filters through the atmosphere during transit events.

We should be hearing a lot more from the IRD-SSP project. Lead author Hiroki Harakawa has this to say:

“Ross 508 b is the first successful detection of a super-Earth using only near-infrared spectroscopy. Prior to this, in the detection of low-mass planets such as super-Earths, near-infrared observations alone were not accurate enough, and verification by high-precision line-of-sight velocity measurements in visible light was necessary. This study shows that IRD-SSP alone is capable of detecting planets, and clearly demonstrates the advantage of IRD-SSP in its ability to search with a high precision even for late-type red dwarfs that are too faint to be observed with visible light.”

Image: Periodic variation in the line-of-sight velocity of the star Ross 508 observed by IRD. It is wrapped around the orbital period of the planet Ross 508 b (10.77 days). The change in the line-of-sight velocity of Ross 508 is less than 4 meters per second, indicating that IRD captured a very small wobble that is slower than a person running. The red curve is the best fit to the observations and its deviation from a sinusoidal curve indicates that the planet’s orbit is most likely elliptical. Credit: Harakawa et al. 2022.

The authors are interested in the question of eccentricity, pointing out that it may offer early clues to the planet’s origin, although it will take further radial velocity measurements to clarify just how eccentric this orbit is. The paper examines four different scenarios to explain the RV data, but none of these constrain the eccentricity conclusively. From the paper:

…there remains the possibility that Ross 508 b is in a high-eccentricity orbit. In a multiple-planet system, migrated planets experience giant impacts or are trapped in a resonant chain (e.g., Ogihara & Ida 2009; Izidoro et al. 2017). Planetary eccentricities are excited by giant impacts. The eccentricity of a planet can be also excited by gravitational interactions between neighboring planets or secular perturbations from a (sub)stellar companion on a wider orbit. The confirmation of a long-term RV trend will help disentangle the formation history of the super-Earth Ross 508 b.

It’s also far too early to make any statements about this planet’s habitability. For one thing, the inner edge of the habitable zone at Ross 508 is not well understood, depending as it does on the star’s luminosity, which in turn is affected by its low metallicity. It does appear that the planet is near the runaway greenhouse limit. But our knowledge of super-Earth habitability is nascent. Climate, plate tectonics, and other potent factors would play a role that we won’t be able to measure until we can start taking atmospheric measurements with next generation telescopes.

Ross 508 b is one of the faintest, lowest-mass stars with a planet detected through radial velocity. Its discovery points to the need for a large telescope and a high precision spectrograph in the near infrared to analyze the planetary systems around this kind of star. We should be learning a great deal more about late M-dwarfs as we press on with projects like the IRD Subaru Strategic Program, coupling near infrared RV work with transit observations from space and ground-based observatories.

The paper is Harakawa et al., “A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone around the M4.5-dwarf Ross 508,” Publications of the Astronomical Society of Japan 30 June 2022 (full text).

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{ 46 comments… add one }
  • Antonio August 5, 2022, 9:40

    I wondered whether JWST could do this kind of research too, but after searching the web it doesn’t seem likely. This spectrograph has R=70000 and JWST’s NIRSpec has R=2700.

  • Henry Cordova August 5, 2022, 10:36

    We should continue to remind ourselves that both the Doppler/Radial Velocity and the Photometry/Transit detection methods highly favor systems whose orbital planes are inclined towards our own solar system. Also, massive planets orbiting very close to very low-mass stars tend to be much easier to detect. We are not looking at a random sample.

    Yes, we all know this, but it still is very easy for selection effects to skew our general perception of the configuration of exoplanets and their stars. Whatever we may be able to learn about any one system in particular, there will always be unconscious biases about the properties of planetary systems in general.

    As far as astrobiology and SETI are concerned, sun-like systems may still be the ones that matter.

    • Antonio August 5, 2022, 16:28

      “As far as astrobiology and SETI are concerned, sun-like systems may still be the ones that matter.”

      That’s the biggest bias of all.

      • henry August 5, 2022, 23:43

        Actually…you may be absolutely right…

  • Michael Fidler August 5, 2022, 10:51

    This may work well on Barnard’s Star for planet b but long orbit of 232 days may take awhile. With a mass of 3.24 earths it should show well and it’s +5 north latitude is almost directly over the Subaru telescope in Hawaii. Barnard’s Star is listed as a flare stare but not very often, from Wikipedia;

    “1998 flare
    In 1998 a stellar flare on Barnard’s Star was detected based on changes in the spectral emissions on 17 July during an unrelated search for variations in the proper motion. Four years passed before the flare was fully analyzed, at which point it was suggested that the flare’s temperature was 8,000 K, more than twice the normal temperature of the star. Given the essentially random nature of flares, Diane Paulson, one of the authors of that study, noted that “the star would be fantastic for amateurs to observe”.

    The flare was surprising because intense stellar activity is not expected in stars of such age. Flares are not completely understood, but are believed to be caused by strong magnetic fields, which suppress plasma convection and lead to sudden outbursts: strong magnetic fields occur in rapidly rotating stars, while old stars tend to rotate slowly. For Barnard’s Star to undergo an event of such magnitude is thus presumed to be a rarity. Research on the star’s periodicity, or changes in stellar activity over a given timescale, also suggest it ought to be quiescent; 1998 research showed weak evidence for periodic variation in the star’s brightness, noting only one possible starspot over 130 days.

    Stellar activity of this sort has created interest in using Barnard’s Star as a proxy to understand similar stars. It is hoped that photometric studies of its X-ray and UV emissions will shed light on the large population of old M dwarfs in the galaxy. Such research has astrobiological implications: given that the habitable zones of M dwarfs are close to the star, any planets would be strongly influenced by solar flares, winds, and plasma ejection events.”

    2019 flares
    “In 2019, two additional ultraviolet stellar flares were detected, each with far-ultraviolet energy of 3×1022 joules, together with one X-ray stellar flare with energy 1.6×1022 joules. The flare rate observed to date is enough to cause loss of 87 Earth atmospheres per billion years through thermal processes and ≈3 Earth atmospheres per billion years through ion loss processes on Barnard’s Star b.

    Hopefully we will have some results in a year or two.
    Proxima is too far south and a violent flare star…
    But there is a long list of red dwarf stars within 40 light years and many will fit the bill for the Subaru Telescope IRD (InfraRed Doppler).

    • andy August 7, 2022, 4:14

      Unfortunately it looks like Barnard b doesn’t actually exist.

      Lubin et al. (2021) “Stellar Activity Manifesting at a One-year Alias Explains Barnard b as a False Positive”
      https://ui.adsabs.harvard.edu/abs/2021AJ….162…61L/abstract

      The interpretation of Barnard b as a false positive is also confirmed in the following paper (which also calls the radial velocity evidence for Proxima c into question):

      Artigau et al. “Line-by-line velocity measurements, an outlier-resistant method for precision velocimetry”
      https://arxiv.org/abs/2207.13524v1

      • Paul Gilster August 7, 2022, 5:55

        Had not seen this one. Thanks, andy. That’s a major finding.

      • Michael Fidler August 8, 2022, 10:30

        Tu Andy, I see what they mean; “This result highlights the challenge of analyzing long-term, quasi-periodic activity signals over multi-year and multi-instrument observing campaigns.”
        I hope the Subaru Doppler can do better and are there any planned observations of these two by JWST?

  • Martyn Fogg August 5, 2022, 10:56

    Tidal heating on this world must be quite significant.

  • Brett August 5, 2022, 12:03

    If it’s tidally locked, I wonder if the far side of the planet would act as a heat sink that would help it avoid a runaway greenhouse effect. Unless the atmosphere is really thick, that cold, dark far side is going to draw off and radiate away a lot of the heat the planet absorbs in sunlight.

    • Mike Serfas August 7, 2022, 19:05

      Some of the Kopparapu, 2017 paper ( https://arxiv.org/pdf/1705.10362.pdf ) seems to agree with that. There were some things for me to learn just from the introduction… Apparently Earth and Venus are not merely two different circulation patterns, but pretty much the two main types of circulation patterns, with a 5-day rotation period marking the approximate boundary between them. So any slow-rotating or locked planet can accumulate a dayside cap of water vapor in a “moist greenhouse”, over a lower atmosphere with a temperature of just 280 K. I assume that radiates its heat away on the night side where there is less water vapor built up? It would be great if someone here could draw us a nice picture of what’s going on, figuratively and perhaps literally.

  • andy August 5, 2022, 15:44

    An interesting consequence of studying late-type M-dwarfs is that their presumed lower levels of flare activity may offer a planetary environment more conducive for life than their younger cousins, with a surface less frequently bathed in flare-induced radiation.

    Careful! The term “late-type” doesn’t have anything to do with the star’s age but refers to the temperature: the contrasting term is not “young” but “early-type” (i.e. warmer, and in the case of main sequence stars, more massive). This rather confusing situation is a legacy of outdated theories of stellar evolution.

    As far as I’m aware late-type M-dwarfs have flare activity that dies off more slowly with age (possibly related to the stars having fully convective interiors), making them potentially more hostile environments for habitability.

    • Paul Gilster August 5, 2022, 19:36

      Good point, andy. Thanks for the clarification.

    • charlie August 6, 2022, 20:35

      andy,
      this an aside but how did u “ghost- out” the text
      “An interesting consequence of studying late-type M-dwarfs is that their presumed lower levels of flare activity may offer a planetary environment more conducive for life than their younger cousins, with a surface less frequently bathed in flare-induced radiation.” ?????

      • andy August 7, 2022, 9:56

        Use the blockquote HTML element to mark up the text.

        <blockquote>Quoted text goes here</blockquote>
        (In case the blog software mangles it, the < sequence is supposed to be a less-than symbol, and > is supposed to be a greater-than symbol)

        • charlie August 7, 2022, 18:43

          like

          Quoted text goes here

          ????

  • James M. Essig August 5, 2022, 18:16

    Most stars in our universe are red dwarfs of which there are about 10 EXP 24 in the presently observable portion of our universe, a tiny miniscule portion of our universe.

    The number of red dwarfs in the observable portion of our universe is about equal to the number of fine grained table salt grains such as commonly available at the grocery store that would cover the entire United States 100 meters deep.

    All red dwarf stars will live for at least on the order of one trillion years and a large fraction of these will last 10 trillion to 30 trillion years.

    So, think of all of the cultural, scientific, technological, theological, medical, social, psychological, and spiritual progress any ETI or UTI personal lifeform species can make over the next few trillion years.

    Should we humans colonize planets orbiting such stars, we likewise have the option of making such progress also.

    Now, the coolest Red Dwarf stars are only about 12 percent of the diameter of the Sun and would appear Cherry Red in color up close. These stars output only about 0.01 percent of the power of stars like our Sun.

    So, planets can orbit such stars at a distance of a mere one million miles or so and still be in the habitable zone. With sufficient planetary atmospheric greenhouse gas content, the habitable zones might be extended to several million miles.

    On a planet orbiting a low end Red Dwarf in the habitable zone, the red dwarf star would appear much larger than our Sun from Earth but also a nice cherry or scarlet red. The starsets and rises on these planets would appear as deep red perhaps even reddish brown orbs. These starsets in their color would be a good back drop for a nice meal of barbecued beef, pork, chicken, and even a Thanksgiving turkey meal: the color of the starsets and rises would closely match typical barbecue sauces.

    As it turns out, we have a red dwarf as the second closest extra-solar star, Barnard’s Star, at only 5.9 light-years distant from Earth. We could reach this star in a few decades with large but reasonable mass ratio space-arks powered by nuclear fission reactors.

    Having sex in the dark redish-brown light of a red dwarf star set to me sounds like it would be a whole lot of fun.

    Other luminaries may develop after the main sequence stars largely all burn out. Such stars may be related to dark matter and/or concentrations of dark energy that morphs into luminous stars.

    Additionally, it is plausible that dark energy gradually decays into standard model hydrogen of protons and electrons which can be the perpetual source of new red dwarfs as the universe evolves.

    • Spaceman August 6, 2022, 15:13

      @James M. Essig: As someone who appreciates these kinds of estimates, can you please explain how you arrived at the number of red dwarf stars in the observable Universe as being approximately equal to the number of salt grains that could cover the entire United States to a depth of 100 meters?

      • Alex Tolley August 7, 2022, 1:13

        I do know that all the stars in the universe exceed the number of grains of sand on all the world’s beaches. You can make that estimate yourself by plugging in some guesstimates.

        IDK about salt depth on the continental USA, but again, you can make an estimate starting with salt here and here. The rest should be easy.

      • Spaceman August 7, 2022, 11:20

        *There are 4213.03 grains of salt in one cup.
        *1 cup = 0.236588 L
        *Grains of salt in one liter = 4213.03/0.236588 = 17807 grains of salt in 1 Liter.
        *1 Liter = 1000 cm^3.
        *There are estimated to be around 200 sextillion stars in the observable Universe with ~70% of those stars being red dwarf stars; therefore, there are approximately 140 sextillion red dwarf stars in the observable Universe.
        * (17807/1000 cm^3)(140 sextillion/ x cm^3)–> 7.86 x 10^21 cm^3.
        *Taking the cube root of 7.86 x 10^21 cm^3 = 19882646 cm.
        So, imagine a giant cube that has a length, width, and height of 19882646 cm. How many miles are in 19882646 cm? According to google, there are 123.5 miles in 19882646 cm. We now have a big salty cube with a volume of 1883652 cubic miles, right?! How does this compare to a cube that is, let’s be rough here, 3000 miles by 2000 miles by 0.062 miles (100 meters)?

        **Well-proportioned salty cube = 1883652 cubic miles
        **Wide and long but not so tall cube = 391200 cubic miles

        Therefore, the number of red dwarf stars in the observable Universe is easily comparable to the number of grains of salt that would cover an area approximately equal to the lower 48 United States to a depth of 100 meters. In fact, 1883652/391200 = 4.81 (adding in the area of Alaska and Hawaii would reduce this factor but not by much).

        Could someone please confirm the veracity (or lack thereof) of this calculation? LOL

        • Alex Tolley August 7, 2022, 19:44

          Area of USA = 9,833,520 km^2
          (round up to 1E7 km^2)
          = 1E13 m^2
          at 100 m deep => 1E15 m^3

          Using your 17807 grains/L
          (round to 2E4 grn/L)
          1 m^3 = 1E3 L
          Therefore 2E7 grn/m^3

          = 1E15 x 2E7 = 2E22 grn/(USA area x 100m deep)

          140E21 red dwarf stars = 1.4E23.

          1.4E23 > 2E22

          Therefore red dwarfs in universe > grains of salt 100 m deep over USA

          Spaceman: “Could someone please confirm the veracity (or lack thereof) of this calculation? ”

          (in the voice of the computer from BBC’s Blake’s 7) Zen:
          “Confirmed”

      • James M. Essig August 7, 2022, 20:52

        Hi Spaceman,

        I’d be happy to.

        Here we assume that a grain of common table sugar is about one millimeter wide.

        So a cubic kilometer of such sugar grains will have 10 EXP 18 sugar grains or one million millimeters by one million millimeters by one million millimeters in size.

        Now take the one kilometer cube and cut the cube into ten one-hundred meter thick slabs and spread the slabs out side by side. Now you have a ten square kilometer slab. Now multiply the ten square kilometer slab by 0ne million to obtain a slab of 10 million square kilometers which is about the area of the entire United States. As such, you accordingly multiply 10 EXP 18 by one million to obtain 10 EXP 24 sugar grains.

        Now the mass of the visible matter in the observable portion of our universe is about 10 EXP 49 metric tons whereas the mass of a red dwarf is about 10 EXP 26 metric tons. Since most stars are red dwarfs, and a large portion of the visible gas is apportioned to red dwarfs, we have about the correct ballpark figures. Large stars such as O, B, A, and F class are much, much, less common than red dwarfs as are G class stars.

        Note that these are merely estimates than depend on the actual amount of visible matter in the universe. We still do not have a final result for the totality of visible matter in the universe.

        Since there are indeed about 10 EXP 24 stars in the observable universe, and most of them are red dwarfs, I have a reasonable first order approximation.

    • Adam Crowl August 6, 2022, 19:53

      Hi James
      Red dwarf stars don’t get much cooler than about 2000 C according to most models – and that’s “white hot” by the usual spectral guides used in foundries. Cherry Red is about 800 C, which is far too cool for a red dwarf in the Main Sequence.

      Know Temperature when metal glows red [anything past 1200 C/2200 F is “white hot”]

      The bottom of the Main Sequence – the very lowest mass Main Sequence star – has a temperature of 2075 K, meaning it would loom 7.74 times larger in the sky than our Sun at the same insolation level. Every so often there would be brighter spots thanks to flares.

      What would be very different is the sky, since the blue light levels are very low, so you might see stars, if there’s minimal high altitude dust. I’m not exactly sure how to compute sky brightness, so I leave it as an exercise for the reader.

      Adam

      • James M. Essig August 7, 2022, 21:02

        Not sure that is correct. Red dwarfs look red for a reason even in space. The atmospheric attenuation of the blue and near blue photons would likely cause the stars to look quite red on the planets.

        Additionally, we have the effects of star sets which would redden the visible starlight just like what happens on Earth. The star sets would thus be far redder than sunsets on Earth.

        Regarding the distance of the stars from habitable planets, that very much depends on the planetary atmospheric physics.

        • Adam Crowl August 8, 2022, 8:40

          Hi James
          They’re called “Red Dwarfs” because of the peak of their spectral distribution lies in the red and infra-red part of the spectrum, but otherwise they approximate a black body radiating at a specific temperature. Colder objects, like Brown Dwarfs, start looking different to black bodies because of the formation of molecules.
          As for the colour index for metals, we’re talking about what’s seen by the human eye – above a certain intensity, the eye perceives “white”. The colour of the light that a black body casts upon objects is quite different to the perceived colour of the light source. Up close to a Red Dwarf we would see it as “white hot” – but mostly the illumination from them will be orange-yellow, changing the colour response of the landscape around us. Certainly no Red Dwarf will cast “cherry-red” light. That requires much cooler light sources.
          As for spectral lines, absorption lines are produced by elements in the spectra of stars. Most of the light of Star-hot gas is continuum emission, not line emissions. Moving gases tend to smear out the lines. You also see strong line emissions typically from chemical reactions at fairly low temperatures with low turbulence.

          • James M. Essig August 14, 2022, 23:40

            Well not exactly. The Sun certainly looks yellow to me when I glance at it and even looks red at sunset.

            There is something wrong with your analysis.

            The Sun at sunset definitely looks quite red. So a red dwarf set on an Earth like planet would look even cooler most likely a brownish red and will look red well before sunset and in the sky.

            Fireworks have a full visible range of colors but all burn at about the same temperatures.

            Regarding emission spectra at low temperatures, the emission spectra also comes from hydrogen and helium atoms etc having electron state energy changes.

            However, I must say that Doppler shifting of stellar surface emission lines is actually a negligible effect because the velocities of gases are not relativistic.

          • James M. Essig August 15, 2022, 23:08

            I cry Uncle on this one.

            After looking at various references, I determined that a red dwarf will most likely not look cherry red on an Earth-like planet hosted by the red star. Even an angular flux density of 1/81 that of the Sun at Earth’s surface will likely overwhelm the optic nerve and still be perceived as white.

            So, my daydream of seeing a cherry red star at high-noon was a bit flaky but it was fun while it lasted.

            Still, the idea of having a star with 4 to 8 degrees of angular diameter would be whimsical and far-out.

            If I annoyed anyone with my bold proclamations, my complete apologies. I was really wedded to the cherry red star at high-noon notion, but as the saying goes, hoping that something is true will not make it any truer.

      • James M. Essig August 7, 2022, 21:26

        As for white hot metal objects undergoing metal working, a 2,000 K metal object will have strong metallic-specific differences in color. The same is true regarding gases and plasmas.

        Some metals have differing frequency specific emissivities depending on elemental composition even while at the same temperature. The same is true for hot gases.

        • James M. Essig August 14, 2022, 23:52

          Also note that the angular area flux density from a red-dwarf can be as low as about 1/81 times that of the Sun. As such, the flux density may very well be low enough to appear cherry red.

          Additionally, the color of stars can be distinctly seen in certain places of high altitude and low humidity levels. My brother has seen this himself.

  • Christopher Phoenix August 5, 2022, 18:25

    This is a rather interesting discovery, and another reminder that our achievements in astronomy and space science are entirely dependent on our instruments. I await the coming generation of >30m class telescopes with great interest.

    We mustn’t overlook the fact that long before we can send any probes to another star (let alone any astronauts), we will be thoroughly investigating those systems by remote sensing. It would be impossible to create a rational plan for an interstellar probe without doing this.

    Our remote sensing capabilities have come a long way… in fact, longer than researchers in early decades recognized to be possible. Some early authors on the subject of interstellar travel concluded that we would have no way to determine the presence of planets around a star before dispatching a crewed generation ship there. An example is James Strong in Flight to the Stars: An Inquiry Into the Feasibility of Interstellar Flight (1965), in which he states that a generation ship crew must be outfitted to survive under entirely inhospitable conditions, as there will be no guarantee of finding a hospitable planet at the destination, and no way to know ahead of time if there is one.

    Now the idea that we would have starships before we figured out a way to detect exoplanets seems rather quaint.

    • Neil Stahl August 7, 2022, 15:50

      If there is a asteroid belt with a variety of heavy metals available then a generation ship crew that hasn’t degenerated should have access to the information needed to exist, even thrive, by using those resources. That should all be verifiable before launch.

      • Christopher Phoenix August 11, 2022, 15:48

        I agree, if the initial generation ship was properly outfitted, asteroids and comets would be sufficient to create colonies. It’s quite possible that the crew might prefer to live in space after living in an artificial environment for centuries, rather than take their chances with heading back down a gravity well. This is the idea behind concepts like Dandridge M. Cole’s macrolife.

        However, it’s a lot less likely that the bean counters back home will sign off on an interstellar flight to reach mere asteroids. After all, we have plenty of those in our own solar system, and we could conceivably bring useful materials back to Earth from them. Not so over interstellar distances.

        Also, I’d not assume that a generation ship could successfully “reproduce” itself unless outfitted for it to begin with, however. If the initial plan was to make a landing on a potentially habitable exoplanet, the mission planners may have decided to ditch everything except landers and short term life support before commencing deceleration. If rockets are used, every ounce of weight cut from the deceleration phase will reduce propellant requirements dramatically.

        I’ve seen at least two conceptual interstellar vehicles designed like this… but that’s a story for another day.

      • Wojciech J August 19, 2022, 5:59

        I would go even further and argue that that presence of an asteroid belt or any other celestial bodies outside of planets would make the planetary colonization(in itself costly and difficult) unnecessary in the first place.

  • Raffaele Antonio Tavani August 5, 2022, 21:05

    Non si sente più parlare, del pianeta Ross 128b.
    È possibile, che ci sia, qualche ricerca in merito? Nuove osservazioni, nuovi aggiornamenti?

    Un saluto, a tutti I lettori, di questo splendido “blog” scientifico.

    • Paul Gilster August 6, 2022, 8:03

      Via Google Translate:

      We no longer hear of the planet Ross 128b.
      Is it possible that there is some research on this? New observations, new updates?

      Greetings to all readers of this splendid scientific “blog”.

  • Edwin August 6, 2022, 6:31

    Hi Paul

    Thanks for the post, really interesting as always and the comments here are always interesting too

    Cheers Edwin

  • Brian Altmeyer August 6, 2022, 7:56

    This sounds like fun. What does a 4 Earth-mass planet even look like? So many ambiguities to unravel.

  • wdk August 6, 2022, 17:24

    This is exciting news and a lot to digest – on just what has been discovered. But in the early discussion, I would like to get some clarification. Perhaps others might share my confusion. Because with “late” and “early” and M dwarfs, we could be talking about “early” and “late” in the spectrum which would be M0 to M9… or we could be talking about age since formation. And this all has some consequence for color, mass, brightness and temperature, displayed on H-R diagrams, sometimes separately and sometimes sharing axes.

    Now M dwarfs form at various times in galactic history just like other stars. However, their migration after formation on the H-R diagram with respect to time is slower than brighter or more massive stars even in the early stages of ignition. But if they are as old as our sun, that formation process would be long past – unless we have a truly young M dwarf star of a couple hundred million years of age. Hence there would be surrounding circumstellar dust amidst of which could be planets. Older systems such as Trappist-1 system the orbital lanes are cleared.

    On the other hand, detectable M dwarfs started with the brightest, either by proximity or mass. Since the more massive M designations are lower numbers 0, 1, 2, 3… one could describe them as early. In fact, dwarfs such as Trappist 1 M8 didn’t come along until “late”. And if you have an M9 in your scope, well maybe you have a brown dwarf.

    It is my guess that the spectral numbering is where the early and late come into play. A verification matter, but I hope it helps.

    • wdk August 7, 2022, 20:45

      Regarding the previous query, searching the paper I note a couple of characterizations.
      1. the spectral type characterization by the authors is M4.5 ( in the abstract ),
      2. later they speak of mid to late M dwarfs.
      I suspect that nailing down Ross 508 a was a significant part of the problem as well as extracting data about b.

      With regard to b, when the table for orbital elements is examined a couple of things can be noted.

      1. The minimum mass estimate based on RV would be the case when transits would occur. So far this is not the case – and a likely mid value for inclination to the line of sight would be about 45 degrees with perhaps another 1.4 factor for mass.
      2. The several models in the paper’s table 3, center around a a planetary orbital eccentricity of about 0.3. Even assuming synchronous period of day and year, it would be hard to picture uniform exposure of subsolar and anti-subsolar hemispheres ( 100 and zero percent) to the primary.
      And this would also make a tidal locking more difficult as well. If we take our moon as an example, its angular rate is constant, so we do get some peaks beyond +/- 90 degrees from Earth Sun line. Then another possible change local thermal conditins would be a obliquity to the orbital plane for the axis. So, if the planet has an atmosphere or fluid oceans, I would bet on weather. The day’s duration? Well….With respect to its orbital period, maybe like Mercury’s.

  • James M. Essig August 7, 2022, 21:12

    Red Dwarfs are not just red because of black body radiation, there are also emission spectra and absorption lines in the stellar spectrum.

    Some very, very, hot things look red such as emergency highway flares. I believe some of these burn at near 2,000 K.

    Common fireworks display a wide variety of colors from red to violet and the combustion processes are all on the order of 2,000 K.

    • Mike Serfas August 8, 2022, 8:18

      We shouldn’t really compare fireworks, which are deliberately designed to produce spectra dominated by a few lines. I think it’s better to compare a candle flame at 1700-1800 K and a formerly ordinary 60-watt incandescent bulb at 2400 K. Atmospheric effects would dominate over this, and we can expect a red dwarf to much more often have a red or orange cast compared to the Sun. When seen through the clouds it will not be “true white”. The effect will be subtle, not dramatic, nearly comparable to moving from a room with fluorescents to a room with incandescent light. To my untrained eye, the stars in the sky really seem much the same color; it takes considerable imagination to perceive much besides Mars as even reddish, though dim red dwarfs wouldn’t be visible there.

      Our retinas might perhaps have too much invested in blue frequencies for such an environment – but retinas routinely deal with many orders of magnitude differences, and our current trichromat color scheme is a recent and somewhat unsteady expansion from a former two-color scheme that leaves much room for improvement. From a biological point of view, the difference is minor and the brain is meant to adapt. Psychologically, however, we can imagine the thoughts of people living on a planet, a star, not really meant for them. They might be guided by religious ideas to think of Earth alone as a deliberate creation, whether of god or anthropic principle, and every other planet as an accidental byproduct. I picture some filtering out of a meeting at their arc-lit Cathedral where they have enshrined every stone and strut and quote they could find from Earth, and looking out at the home where they were raised with a jaundiced eye.

      • Antonio August 9, 2022, 17:06

        “Psychologically, however, we can imagine the thoughts of people living on a planet, a star, not really meant for them. They might be guided by religious ideas to think of Earth alone as a deliberate creation”

        Non-sense. By the time we start colonizing exoplanets, we would already have colonized the entire Solar System long ago, with a wide variety of environments. So no such psychological trauma at all, nor such geocentric preference or even “habitability” preference (i.e. liquid water on the surface).

    • Alex Tolley August 8, 2022, 10:48

      LED bulbs are temperature rated. A “warm 2700C” bulb looks yellow to our eyes (similar to an incandescent tungsten filament bulb), so unless there is something very different between red dwarf star spectra and LED spectra, the stars would look yellow to us, just like the liquid metal from a furnace.

    • Alex Tolley August 8, 2022, 11:29

      We should bear in mind that we don’t see the unbiased spectrum, but rather what our eyes are capable of seeing. So we would see the color of a star differently from that of a bird, a dog, or a bee.

      This website What Color are the Stars? attempts to show the colors of stars as we would see them if not to intensely bright (saturate the cones) or too dim (only the rods activeated).

      M dwarfs appear orange, rather than red as depicted in the HR diagrams, and this is indeed how paintings by the better astro artists depict them.

      In the case of Ross 508b, because the star would appear so large to our eyes due to its distance, the brightness would be greater and hence would appear whiter than from a planet further out, i.e. less orange and more yellow. Of course, then we have the issue of the planet’s atmosphere, which may well redden it considerably at sunset, depending on its surface density, composition and whether or not there is much dust.

      Anyone want to attempt to determine what color it may appear at sunset to a protected human on the surface given some specified parameters for the planet’s atmosphere?

  • Robin Datta August 9, 2022, 6:15

    Primates are a small branch in the vast evolutionary tree.

    Color vision in primates

  • ljk August 17, 2022, 12:44

    One Exciting way to Find Planets: Detect the Signals From Their Magnetospheres

    https://www.universetoday.com/157162/one-exciting-way-to-find-planets-detect-the-signals-from-their-magnetospheres/

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