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Astrobiology

Earth-Mass Planet Orbits Proxima Centauri

By Keith Cowing
NASA Watch
August 24, 2016
Filed under
Earth-Mass Planet Orbits Proxima Centauri

Earth-mass Planet Found In The Habitable Zone Of Proxima Centauri, ESO
“Astronomers using ESO telescopes and other facilities have found clear evidence of a planet orbiting the closest star to Earth, Proxima Centauri. The long-sought world, designated Proxima b, orbits its cool red parent star every 11 days and has a temperature suitable for liquid water to exist on its surface. This rocky world is a little more massive than the Earth and is the closest exoplanet to us — and it may also be the closest possible abode for life outside the solar system. A paper describing this milestone finding will be published in the journal Nature on 25 August 2016.”

NASA Watch founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.

53 responses to “Earth-Mass Planet Orbits Proxima Centauri”

  1. PeteK says:
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    Very cool discovery. Lets go visit our neihbor

  2. Ben Russell-Gough says:
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    Certainly within reach within a human life-time using extant technology. A suitable target for a flagship-class mission, I think! It’s just a matter of launching a large enough fuel tank!

    • Tritium3H says:
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      “Certainly within reach within a human life-time using extant technology. “
      Huh????????

      • Ben Russell-Gough says:
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        Yup! Look up nuclear thermal propulsion and nuclear electric propulsion! We’re still talking about a total mission duration similar to that of the Voyager-1 probe (40 years) but it can be done!

        • Tritium3H says:
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          Hello Ben,

          NTP and NEP are conceptual technologies, that might one day be suitable for interplanetary missions (within our solar system). Neither are suitable for interstellar travel…and NEP is not capable of accelerating a vehicle to 10% c within a human life-time.

          • fcrary says:
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            I agree about the inviability of a quick trip to Proxima Centauri. But I don’t think it’s fair to call nuclear electric propulsion a “conceptual technology.”

            Electric propulsion is in common use for communications satellite station keeping, and the NSTAR/NEXT line of thrusters has been used on the Deep Space One and Dawn planetary missions. Those are all solar electric, but as far as the thruster is concerned, you just need to plug it in. It doesn’t care what provides the electric power. (In ground test, they plug the into the wall socket. Well, the plug a high voltage power supply into the wall socket and the thruster into the HV power supply.)

            Nuclear reactors have been flown on Earth orbit. Real ones, not RTGs. That was a long time ago. I think the last ones flown were Soviet TOPAZ reactors back in 1987. Developing and flight qualifying a modern reactor would take some work. But I wouldn’t call the idea “conceptual.”

            The step of plugging the electric propulsion system into the reactor doesn’t strike me as a huge development effort.

          • Tritium3H says:
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            Hello fcary,

            I grant you that NEP is beyond conceptual, in the sense that we have the “technology” to develop a high power density, space-rated nuclear reactor. Although, even with a crash program, we might still be talking decades in the future. Nevertheless, an NEP vehicle would be strictly interplanetary. There just is NO WAY that an NEP vehicle could carry enough reaction mass (e.g., Argon) to provide continuous acceleration for decades. As the reaction mass is finite, the vehicle’s final Delta-V will be limited to a some multiple of the max. exhaust velocity. I can’t conceive of even a notional NEP-based vehicle reaching 0.1% speed of light, much less 10% c. This puts an NEP-based Proxima B expedition into a mission time measured in thousands of years.

          • fcrary says:
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            I think 0.1% c is optimistic. Almost off the top of may head (which is to say, not even at the back-of-the-envelope level of accuracy) here’s what I think we could do: With 25 years of development and a launch on something a bit larger than an SLS (or multiple Falcon Heavy launches with on-orbit refueling) we _might_ be able to get a 5-tonne spacecraft to 0.05% c after 50 years or so under thrust. And that would consume about 300 tonnes of xenon; according to Wikipedia, the world production rate is about 50 tonnes per year.

            Since there are easier ways to get to Pluto, and that’s not enough to for a viable interstellar mission, I’m not sure why we’d want to. But that’s about what the numbers add up to.

        • Todd Austin says:
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          Lasers might also be used to boost a spacecraft on its way at significant fractions of the speed of light. If you were able to combine lasers for launch and NTP for braking, you might actually get something into orbit at the other end using tech that might reasonably be developed in the next few decades.

        • fcrary says:
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          That would mean averaging about 10% of the speed of light, or 31,600 km/s. Current electric propulsion systems give an exhaust velocity under 50 km/s, and that’s can’t be improved without increasing the power requirements. The rocket equation says that would require an awful lot of fuel (an initial to final mass ratio around 3e274.)

          Electric propulsion also doesn’t give enough thrust to get up to 0.1c in 40 years. I once estimated that, using Deep Space One hardware, you could build a stripped down spacecraft which could manage 6 km/s/year. After 40 years, you’d still only be going 0.0008c.

          • Michael Spencer says:
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            Alas. As I look at the state of our knowledge and compare it to the apparent complexity of the universe we are so paltry, struggling as we do.

            And what a strange place we find ourselves…what is dark matter, dark energy? Why is gravity so inexplicable? Fundamental questions abound. We cannot adequately describe this place in which we find ourselves, this Universe.

            We may have a future amongst the stars, and indeed my own heart yearns for it. But it will come after another millennia, perhaps, struggling to understand in any fundamental way exactly how our universe works. Or multiple millennia, after which we will see the rocket equation as Mr. Ford saw horses, looking back as we skitter amongst the stars via some unseen, for now, mobility.

            This is the explanation for the Fermi Paradox; the Universe is so stunningly inexplicable that peoples struggling for millennia after millennia, finally comprehending the environment in which we live, must be few and far indeed.

            As to humanity there is no fundamental comprehension. Is this place a multiverse, as Brian Green would have us believe, once in an endless universe of universes? Can we ever comprehend such a thing? Is matter even fundamental, or is it simply a by-product of unknown energetic processes? Do strings abound, as Dr. Randall et. al. postulate? Or?

            Nobody knows. Because while the Universe is inexplicable, for now, it is also rich with hints, freely offering via simple observation the secrets to her heart.

            The future is so ripe for exploration and discovery.

          • Ben Russell-Gough says:
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            That’s from a standing start, I think. What if you add a chemical rocket to boost of LEO followed by a Juno-style multiple-flyby, thrusting at every periapsis until the final flyby of Jupiter and continual thrust from there?

          • fcrary says:
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            You could do that. On the other hand, I neglected how much the Sun’s gravity would slow the spacecraft down, when it’s on the way out. Both gravity assists and solar escape velocity aren’t a big deal. You can’t get more than about 50 km/s from a Jupiter gravity assist. Solar escape velocity from 1 AU is 42 km/s (but you start with the Earth’s 30 km/s of orbital velocity.) The 0.0008c I mentioned is 240 km/s. A few dozen km/s at the start isn’t going to help much.

      • Daniel Woodard says:
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        Not necessarily a biological human, but the distinction between AI and biological humans is likely to fade over the next few decades.

        • Michael Spencer says:
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          Alas after I’m gone; but the next century will bring us cyborgs and upload consciousness. And immortality.

          I hope.

          • Daniel Woodard says:
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            Immortality perhaps, but probably not for us. Can a consciousness be uploaded? Possibly, in the sense that we upload what we can of our humanity to our children. To an AI interstellar travel would be less problematic. Just turn off for 500 years, then reboot.

          • Michael Spencer says:
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            Alastair Reynolds writes thoughtfully about a multiple-system humanity possessing near-light speed machines (he calls the, endearingly, “Lighthuggers”).

            He posits a natural separation between planet dwellers and ship crew who see some single place only after perhaps half a century of real time, witnessing a planet’s society like stop motion animation.

  3. Vladislaw says:
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    We are approaching Proxima B Capt. … (read that in Nimoy’s voice)

    Right out of StarTrek

  4. TheBrett says:
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    Neat!

    It’s a pity they can’t seem to find a transit, though. That would really help.

    • Ben Russell-Gough says:
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      It would be just our luck if we’re looking ‘down’ nearly perpendicular to the system’s ecliptic plane!

      • fcrary says:
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        If so, the planet’s mass would be larger. The doppler method only gives mass times the sign of that angle.

        But it wouldn’t take much of a tilt to preclude transits. For a planet orbiting at 0.05 AU around a 0.141 solar radius star, I get a 0.75 deg tilt being enough to ruin a transit geometry. I make that a 1.3% chance the geometry works.

    • Todd Austin says:
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      We should have one or more telescopes in the next few years that will allow us to image the planet directly. Transits won’t be necessary to confirm the existence of the planet and the type of its atmosphere (and, I’m sure, other things).

      • Michael Spencer says:
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        Hmm. Wouldn’t atmospheric characterization depend in large part on some sort of occultation? Might be able to tease details like compositional gasses from spectroscopy, but atmospheric depth and related would need another approach?

        • Todd Austin says:
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          Perhaps the resolution of new ‘scopes will be high enough to do occultation studies using transits of background stars?

          • fcrary says:
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            I think that’s unlikely. You need a star to pass behind the planet, and when the planet is four light years away, that’s a very, very small part of the sky. The odds of a star being there are not good. The other side of the coin is that, the smaller that angle is, the smaller the region on Earth where the occultation can be seen (this is similar to the path of totality during a solar eclipse.) People who do occultations of planets like Pluto tend to use small telescopes they can transport to obscure locations. But for an extrasolar planet occultation, you’d need a big and non-portable telescope. It would be great if it were possible, but I can’t see it happening.

  5. Shaw_Bob says:
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    Poyekhali!

  6. Saturn1300 says:
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    I have been wondering about this for 60 years. One of the great questions in history. They will soon have a lot of information on Proxima-B. Telescope time will be allotted now that they are sure it is there. A corona graph and spectrograph. With all the big telescopes they will surely be able to find out a lot. A cool red dwarf. The easiest to block the star for direct. How can we get exactly what we wanted? The most plentiful star and lasts trillions of years. There must be a lot of these out there. A star about as old as ours. No ET signals, but maybe there are better receivers coming. Maybe funding for that one on the far side of the Moon.

    • Daniel Woodard says:
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      However the planet is very close to the star and likely tidally locked. Orbital period only 12 days.

      • Michael Spencer says:
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        .05 AU! What a shocking number. 4.6M miles! Imagine how the star appears in the sky, hanging there constantly, maybe even following some sort of limited apparent motion depending on many factors including planet obliquity and possibly the remnants of old orbital parameters.

        But still! A giant red ball, hanging in the sky. Substitute that for our own pre-historic and nascent belief systems. God in all of her glory, right there for all to see.

        No moon to regulate the seas nor the affairs of sentient creatures. No moon to provide a sense of time. Only an eternal red mass occupying a huge portion of the sky. How different our own legends would have been. The Aeneid begins every chapter, for instance, with the rosy-fingers of dawn waking the planet- something not seen there.

        And no night. Ever, without a long trip to a (probably) very cold dark side.

        Except for the solar flares, of course. Without the miracle of a strong magnetic field, this planet is dead.

        • Todd Austin says:
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          Note that this is about 2.5 times the distance that Callisto is from Jupiter. Proxima would, indeed, be very large in the sky.

          I would think it more likely for life to develop along the terminator band, perhaps in the shadow of mountains that would provide some shelter from stellar storms, yet be warm and light enough to support life (assuming it in any way resembles life on Earth).

          With such a dramatic contrast in conditions between the illuminated & dark sides, the weather in the terminator band could be pretty wild.

          That all assumes a magnetic field strong enough to protect the atmosphere from being stripped. Though with a larger mass than Earth, it has a decent chance of having a liquid core still, even if it is ~300 million years older.

          • fcrary says:
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            I wouldn’t preclude a magnetic field, since we actually don’t understand dynamo theory very well. Mercury and Ganymede have no business having a core dynamo, but they (probably) do. The stellar wind at Proxima Centaura b would be about 80 times stronger than at Earth, but an Earth-like field could still stand it off by about 3 planet radii.

          • Yale S says:
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            Mercury may have a possibly sulfur contaminated core, and a 59 day rotation (in an 88 day orbit) may be what it takes to keep the 1% magnetic field.

            And Ganymede may have Fe snow in its core.

        • fcrary says:
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          Proxima Centauri is a fairly small star. It’s supposed to have a radius of 0.14 solar radii, which makes it only 40% larger than Jupiter. But, even so, that’s still three times larger than the Sun or Moon, as seen from Earth.

          I had to think a while over your comment about this planet having no moon. Stable orbits around tidally locked bodies are quire possible, but tidal evolution may change that or cause it to impact the planet. But that could take a long time. That’s going to happen to Phobos, but not for another 50 million years or so (43 million, according to one study, which must have been fun to write.) I wouldn’t preclude a moon. Assuming the planet is tidally locked, it would have to be below synchronous orbit and on its way to tidal destruction. But, depending on the details, that could be a billion years off. Other fun possibilities are of a planet which used to have a moon, but lost it as the planet became tidally locked. That could end up with things like capture onto L4/L5 orbits, or a giant impact.

          • fcrary says:
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            Correction. I don’t think a moon would be lost. As the planet moves towards synchronous rotation, planetostationary orbit would move outward, the moon would become sub-synchronous, and then tidally evolve inward. Modeling this sort of thing might make a good project for a first or second year grad student.

      • ProfSWhiplash says:
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        I wonder if, even though tidally locked, such a planet could still rotate about an axis that’s forever pointed towards Proxima? Even though being tidally locked would prevent a planet to spin at any other orientation, having the planet’s axis be tidally oriented along a line towards that sun’s center would just as likely NOT impede planetary rotation. If that’s possible, then there might still be just enough motion to keep an assumed still-liquid metallic core rotating to help foster a magnetic field.

        Of course, assuming if there were such a spin, an observer on the day-side wouldn’t notice any visual difference (just big sun, red sky). Yet on the other hand, the dark side would see the stars circling weirdly around the far-side pole. Weirdly, because first there’d be the planet’s sun-locked axial spin (assuming it’s there), compounded by the 12-day year also giving a periodic change to the night sky. (There’d also be no “stationary” star at the far-pole, like our own Polaris)

        And anyone on the “equatorial” transition region would get to see both by just turning about: a eternally stationary sun-“rise” side on one border, transitioning to dusk to twilight to those circling-sweeping stars at the “night” border.

        • fcrary says:
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          I don’t think that works. The planet’s axis of rotation is fixed, while the planet orbits around its star. If the planet’s spin axis pointed at the star at one time, a quarter of an orbit later it would be pointed 90 deg. from the star. At that phase of its orbit, it would experience tidal damping of its rotation.

        • Daniel Woodard says:
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          For a tidally locked planet the rotation axis is perpendicular to the orbital plane. A twelve day rotation period might induce some magnetism.

      • fcrary says:
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        There is another possibility. The discovery paper only put an upper limit on the planet’s orbital eccentricity. The authors noted that, within that limit, a Mercury-like 3:2 spin-orbit resonance is possible.

        I can also think of other possibilities. Given a large Moon, the planet-moon system would have a very large amount on angular momentum. This could greatly increase the time required for tidal forces to produce synchronous rotation. I don’t know how long, and that calculation would make an interesting paper. But if it is long enough, the planet might not be there yet.

        Finally, having worked on Saturn system science for some time, I’ve seen people discover all sorts of previously unknown resonances. The Mercury-like 3:2 I mentioned may not be the only stable one. The literature is full of examples of resonances noone thought of until they were observed. So I wouldn’t rule that out.

    • fcrary says:
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      If I did the math correctly, a planet 4.224 light years away and 0.05 AU from its star is only 0.04 arcsecond from the star. That’s awful close for a coronagraph. A quick check makes me think the coronagraph on JWST couldn’t manage to split a star and planet with less that 0.5 arcseconds or so of separation.

  7. John_K_Strickland says:
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    Some models indicate that a planet like Proxima b with a thick enough initial atmosphere will not lose it to a freeze-out on the night side. We do not know how accurate such models are, but it is virtually certain to be tidally locked since the star is so very small.

    If the planet is no more than 1.3 times the mass of Earth, and with a comparable density, its diameter will be less than 1.1 Earth diameters or 8,700 miles across. This would probably make it the closest match to Earth of any of the current “Earth-like” exoplanets.

    To be truly “Earth-like”, it needs to have an atmosphere with a comparable density to Earth’s. Note that 1.3 is the lowest possible
    value for this planet, as the detection method is Proxima’s tiny wobble caused by the planet’s gravity. We cannot tell if the orbit could be partly sidewise to us, possibly making the planet larger than it
    seems.

    If the planet is slightly larger, (about 1.1 Earth diameters), the following values would apply:

    Mass – 1.4 of Earths
    Gravity – 1.16 of Earths
    Low Orbit velocity – 8.6 km / sec
    Escape velocity – 12.6 km / sec
    Average Density – 5.8 tons / cubic meter vs Earth at 5.5

    These values are based on a table I created last fall showing a progression of rocky planets using a formula which was provided by Dr. Abel Mendez at Arecibo. This accounts for the slight compression of the rock in the mantle and nickel-iron core up to about 1.5 Earth diameters.

    What we DO NOT know is if there is an atmosphere and if liquid water exists on the surface. Almost all of the air could be frozen out on
    the night side at 40 kelvin or less. It is even more likely that all the water could be frozen on the night side.

    If the planet originally had a lot of water, glaciers could flow onto the day side from the night side all the time, providing it with temporary water. If the planet is in an elliptical orbit, its sunset zone could be significantly expanded. Depending on where the planet is in the habitable zone, a relatively wide ring of surface around the “sunset line” could have mild temperatures.

    People would experience a near-normal gravity on the planet and even if there were no air, a wide zone of the planet along the
    sunset line could be para-terraformed, with extensive pressurized habitats. However, even if the planet was the minimum size, that would still require ~10 km/sec delta-V to land from orbit and the same to take off again.

    This discovery will certainly up the stakes for competition among astronomers to be the first to detect any possible atmosphere and could change funding priorities for planet-detection telescopes. This also ups the odds that other smaller stars have planets.

  8. Yale S says:
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    One problem with Proxima is that it is (like most red dwarfs) a flare star. At random intervals it experiences simply titanic flares sufficient to sterilize any surface close enough to have liquid water. Some very special adaptations would be required for life in the twilight zone. But as Ian Malcolm said.. “life…finds a way.”

    • fcrary says:
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      I’m not too concerned about it being a flare star. If it’s got an atmosphere, the X ray and (most) UV flux from a flare wouldn’t reach the surface. If it has an Earth-like magnetic field, even extreme space weather events (likely for a flare star) wouldn’t be much of a problem either. If it doesn’t have a sufficiently strong magnetic field, it won’t have much of an atmosphere either: We’ve learned a great deal about atmospheric loss from unmagnetized bodies, courtesy of the MAVEN mission. I’m comfortable saying a unmagnetized planet, 0.05 AU from a M class star would not retain much of an atmosphere.

      But, since it is a flare star, I’d expect some intense magnetospheric processes (assuming that magnetic field…) And that raises the interesting possibility of auroral radio emissions. Assuming an Earth-like field, I’d expect something like two orders of magnitude stronger radio emissions than the Earth’s AKR (Auroral Kilometric Radiation.) During extreme events (which might be common) possible an order of magnitude or two greater than that. With the right radio telescope, that might be observable from Earth. I suspect people will be proposing for time on facilities like LOFAR. Unfortunately, for an Earth-like magnetic field, those radio emissions would be below 1 MHz, and therefore unobservable from the Earth’s surface. It would _really_ be nice to have a good radio telescope above the Earth’s ionosphere.

      • Yale S says:
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        “I’m not too concerned about it being a flare star. If it’s got an atmosphere, the X ray and (most) UV flux from a flare wouldn’t reach the surface.”
        I would certainly be concerned.
        As you point out, if it has no atmosphere, surface life is not likely. Yet, if it DOES have a magnetic field, it still will be sterilized. The flares are not solely Xray and UV. They also are streams of protons.
        The current old and quiet Proxima produces a major flare roughly every 20 minutes and a superflare every 3 hours. These superflares reach intensities 100 times the greatest flares the Sun reach and they impact a planet 80% closer to the source. In its younger days, Proxima would been ENORMOUSLY more active.
        The protons from a single superflare will deplete the atmospheric ozone by an estimated 94% within two years, and these occur 8 times per day.
        The surface UV flux would reach up to 10,000 times the flux at the Earth’s surface.
        Plus, even with a planet’s magnetic field (likely low for a planet with an 11 day rotation), the disassociation and heating from the xray and uv flux should strip away the atmosphere.
        Its hard to imaging anything living except in a submerged ocean, like Europa.

        • fcrary says:
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          Well, technically, flares do not involve protons. The solar (well, stellar, in this case) energetic particle events and coronal mass ejections are what give the proton enhancements. They are related to flares (caused by the same event), but people who work in the field are sensitive about the cause and effect confusion that frequently shows up in textbooks and press releases.

          As I said, I think an Earth-like magnetic field would shield the planet from these protons, even in a very intense event. The Earth’s magnetopause standoff distance is about 10 planetary radii, and scales as the 1/6 power of the upstream solar wind pressure. For Proxima Cent. b, at 0.05 AU from a star with about 20% the stellar wind mass flux, that would put the quite-time magnetopause at (0.2/0.05^2)^(1/3) or 4.3 planetary radii out (which, given the uncertainties, is really “about four or five.”) That deflects the thermal plasma, and the energetic protons won’t get much further in: In an Earth-like field, a 1 MeV proton has a gyroradius of 5 km. 4 body radii out, that would go up to 600 km, which still isn’t very far.

          Pushing that in to the surface would take a CME that increased the stellar wind dynamic pressure by a factor of 6300. Even for a flare star, I don’t think that’s not going to happen very often.

          It would, of course, make this a wonderful playground for magnetospheric physics. But it’s hard enough to get a good magnetospheric payload to Jupiter, so I guess I’ll have to keep my expectations realistic.

          I have no idea where you got those 94% and 8 day numbers for ozone depletion. There are also other atmospheric species which absorb UV and X ray photons. I’d say it depends on the thickness and composition of the atmosphere.

          Long-term atmospheric loss is another issue. But, again, I’m not sure if anyone has done any serious calculations or, if so, what assumptions they made. I’ll note that the Earth is subject to exactly those same processes, and the overall impact is more-or-less zero. The overall brightness of Prox. Cent. at 0.05 AU is 68% of the Sun at 1 AU. Since it’s a flare star, the flux at the relevant energies is higher, but I’d make that UV photons around 10-20 eV, not X rays. In any case, how many orders of magnitude do you need to make a negligible process enough to strip off an entire atmosphere?

          • Yale S says:
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            Yes I was loose in my terms. The SPEs appear to source from the same location as the flare and occur at the same time.
            One thing not discussed is CME effects;

            …for a terrestrial exoplanet with size and mass like that of the Earth, at 0.2 AU orbit around a star with M* 0.5 M(Sun), the
            magnetic moment is expected to be in the range of 0.02 – 0.15 of the Earth’s present-day magnetic moment . (
            the number for Proxima b at it slocation around Proxima is 0.08-0.28 time that of Earth.)

            Because of tidal locking of Earthlike
            exoplanets within close-in HZs, weaker
            planetary intrinsic magnetic moments and, consequently, smaller magnetospheres can be expected.
            Furthermore, we found that the difference
            of the mass flux between strong and weak
            CMEs is not as important as the difference between strongly and weakly magnetized Earthlike exoplanets. As a result, the magnetospheric standoff distance for weakly magnetized Earthlike exoplanets at orbits smaller than 0.1 AU can be compressed under the action of the CME plasma flow down to altitudes 1,000 km above the planetary surface. Such interaction of CMEs with a planetary magnetosphere may result in a
            direct exposure of the planetary atmosphere to the stellar CMEs’ plasma flow. This would cause strong atmospheric erosion on Earth-like exoplanets within close-in HZs of active M stars

          • fcrary says:
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            Do you have a reference for that? As I pointed out, Jupiter and Saturn have almost the same rotation rate and composition, but one’s magnetic field is about 20 times greater than the other’s. Rotation rate is not the only thing that matters, and some factors can (apparently) make a much larger difference (e.g. size of the dynamo region and heat flux out of that region.) There are some really poor ways of estimating planetary magnetic field strengths. (There are also some which aren’t too bad, but they still don’t do a very good job of reproducing our own solar system.)

            In any case, I was discussing CME’s, when I wrote: “For Proxima Cent. b, at 0.05 AU from a star with about 20% the stellar wind mass flux, that would put the quite-time magnetopause at (0.2/0.05^2)^(1/3) or 4.3 planetary radii out…”

            If you want, the corresponding value for a planetary field 15% of the Earth’s (in the middle of the range your reference mentions) would be a 2.8 planetary radius standoff distance. And “only” a factor of 500 increase in solar wind dynamic pressure would be required to force the magnetopause into the atmosphere.

            I’m not sure there is any real disagreement about the results of a very weak planetary field. If it isn’t there, the atmosphere would have eroded away, even if Proxima Centauri were not a flare star. If there is a strong (Earth-like) field, then it would stand off the CMEs, even from a flare star. So I don’t think the key issue is the fact that Prox. Cent is a flare star. I think the key issue is the strength of (or existence of) a planetary field. I just don’t think we know; there are enough case in our own solar system which dynamo theory has trouble with.

            I will say again, however, that a good radio telescope above the Earth’s ionosphere would be _very_ nice. That could allow an actual measurement of magnetic field strength.

          • Yale S says:
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            Yes, rotation rate isn’t absolute. Jupiter’s metallic hydrogen (convection zone) is almost larger than the entire planet of Saturn (with its much smaller convection zone).

            That is why the range for the tidal locked Earth’s magnetic strength at Proxima was given as “0.08-0.28” time Earth’s, a factor of 3.

            The reference you requested:
            http://online.liebertpub.co

        • fcrary says:
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          Also, I’m not sure rotation matters for the planet’s magnetic field. Well, obviously it does, since you need differential rotation for a dynamo. But I note that Jupiter and Saturn have the same rotation rate (to within 10%) and similar composition, but Jupiter’s surface magnetic field is a bit over 20 times stronger than Saturn’s. That means there are other, very significant factors involved; a 11-day rotation period doesn’t rule out an Earth-like field. I’m not even sure if it makes it unlikely.

      • Michael Spencer says:
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        As an amateur radio operator I’m imagining the radio bands would be full of static and likely not usable. The development of radio would be stunted, therefore, requiring some other manner of long distance communication. A jump start to light-based devices? Cables?

        • fcrary says:
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          That’s an interesting question, since Aug. 28 to Sept. 2 is 157th anniversary of the Carrington Event. During that event, aurora were observed in places like Havana, Cuba; telegraph operators were sending long distance messages with the power disconnected from the lines (using the induced voltage from the geomagnetic storm.)

          For a planet 0.05 AU from a flare star, I’d say any radio communications involving the ionosphere (like the long-distance AM radio used on Earth) would be totally hopeless. The ionosphere would be doing all sorts of crazy things.

          I’m less certain about the higher frequencies and line-of-sight communications.
          The natural emissions would be broad-band, but not at all frequencies. In the solar system, natural radio emissions (at least the really loud ones) are near or below the electron cyclotron frequency at the source. But that depends on the magnetic field at the source. I honestly don’t know what to expect from an M class flare star or its stellar wind at close distances.

          • Michael Spencer says:
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            Possibly the truly high frequencies could be useful for point to point, at least to some extent.

            But think about how radio developed here (as one model): we started with machines having undifferentiated wavelengths in the range of a hundred to several hundred meters (breaching the Atlantic with spark was a huge and under appreciated achievement).

            But as the “valve” was developed, those wavelengths became shorter as oscillators were available. And bandwidth fell by many orders of magnitude.

            Generating high megahertz and gigahertz devices by Terrans came much later; these frequencies aren’t generated by the spark devices that started the whole thing, as far as I know. When I was first licensed, for instance, the world above around 5 Ghz was rarified indeed.

            In that case, what would be the route to radio? I suppose spark technology could be discovered and used for very short distances; once discovered, the utility of such a device would surely engender research and perhaps the discovery of the diode, tetrode, and finally pentode.

            And from there the technology soars. Earthlings learned via the triode that a very small amount of current could regulate a very large amount, and that with a little feedback we could do all sorts of desirable things. This essential knowledge drove semiconductors (which were initially simple 3-wire devices) and to a large extent our tech-based society.

            And thus ends the (much) compressed history of modern technology from the perspective of an amateur radio operator.

            You heard it first here, folks.