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Thread: Proxima Centauri b: Terrestrial or Neptunian?

  1. #31
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    Correction, that is the wrong link. Yours has 00954 in the url but it should be 00984:

    https://arxiv.org/abs/2003.00984

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." — Abraham Lincoln

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  2. #32
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    Thank you for the correction, greatly appreciated.
    Do good work. —Virgil Ivan "Gus" Grissom

  3. #33
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    You’re quite welcome.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." — Abraham Lincoln

    I say there is an invisible elf in my backyard. How do you prove that I am wrong?

    The Leif Ericson Cruiser

  4. #34
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    A new paper says that the explosive eruptions from Proxima Centauri could have significant effects on the atmosphere of Proxima b, as detailed by the authors. You won't be able to breathe the air, but the planet might be warm. https://arxiv.org/abs/2003.02036
    Do good work. —Virgil Ivan "Gus" Grissom

  5. #35
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    Waiting for confirmation of Proxima c. Maybe a telescope will get it.

    https://arxiv.org/abs/2003.09305

    Expectations for the confirmation of Proxima c from a long-term radial velocity follow-up
    Mario Damasso, Fabio Del Sordo
    (Submitted on 20 Mar 2020)

    Proxima c, a candidate second planet orbiting Proxima Centauri, was detected with the radial velocity method. The announced long orbital period (5.21 +0.26/−0.22 years), and small semi-amplitude of the induced Doppler signal (1.2 ± 0.4 m/s), make this detection challenging and the target worthy of a follow-up in the next years. We intend to evaluate the impact of future data on the statistical significance of the detection through realistic simulated radial velocities to be added to the published dataset, spanning up to one orbital period of Proxima c in the time range 2019-2023. We find that the detection significance of Proxima c increases depending not only on the amount of data collected, but also on the number of instruments used, and especially on the timespan covered by the observational campaign. However, on average we do not get strong statistical evidence and we predict that, in the best-case scenario, in the next 5 years the detection of Proxima c can become significant at 4
    σ level. If instead Proxima c does not exist, the detected signal may lower its significance down to 2σ.
    Do good work. —Virgil Ivan "Gus" Grissom

  6. #36
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    https://arxiv.org/abs/2003.13106

    Orbital inclination and mass of the exoplanet candidate Proxima c
    Pierre Kervella, Frédéric Arenou, Jean Schneider
    (Submitted on 29 Mar 2020)

    We analyse the orbital parameters of the exoplanet candidate Proxima c recently discovered by Damasso et al. (2020) using a combination of its spectroscopic orbital parameters and Gaia DR2 proper motion anomaly. We obtain an orbital inclination of i = 152 ± 14° for the prograde solution, corresponding to a planet mass of mc=12 +12−5 M⊕, comparable to Uranus or Neptune. While the derived orbital parameters are too uncertain to predict accurately the position of the planet for a given epoch, we present a map of its probability of presence relatively to its parent star in the coming years.
    Do good work. —Virgil Ivan "Gus" Grissom

  7. #37
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    A powerful effort to find Proxima Centauri c optically has ended without a definite answer: was it a planet that was detected or just noise?

    https://arxiv.org/abs/2004.06685
    Searching for the near infrared counterpart of Proxima c using multi-epoch high contrast SPHERE data at VLT
    R. Gratton, et al.
    (Submitted on 14 Apr 2020)
    Proxima Centauri is known to host an earth-like planet in its habitable zone; very recently a second candidate planet was proposed based on radial velocities. At quadrature, the expected projected separation of this new candidate is larger than 1 arcsec, making it a potentially interesting target for direct imaging. While difficult, identification of the optical counterpart of this planet would allow detailed characterization of the closest planetary system. We searched for a counterpart in SPHERE images acquired during four years through the SHINE survey. In order to account for the large orbital motion of the planet, we used a method that assumes the circular orbit obtained from radial velocities and exploits the sequence of observations acquired close to quadrature in the orbit. We checked this with a more general approach that considers keplerian motion, K-stacker. We did not obtain a clear detection. The best candidate has S/N=6.1 in the combined image. A statistical test suggests that the probability that this detection is due to random fluctuation of noise is < 1% but this result depends on the assumption that distribution of noise is uniform over the image. The position of this candidate and the orientation of its orbital plane fit well with observations in the ALMA 12m array image. However, the astrometric signal expected from the orbit of the candidate we detected is 3-sigma away from the astrometric motion of Proxima as measured from early Gaia data. This, together with the unexpectedly high flux associated with our direct imaging detection, means we cannot confirm that our candidate is indeed Proxima c. On the other hand, if confirmed, this would be the first observation in imaging of a planet discovered from radial velocities and the second one (after Fomalhaut b) of reflecting circumplanetary material. Further confirmation observations should be done as soon as possible.
    Do good work. —Virgil Ivan "Gus" Grissom

  8. #38
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    More on the image of "Proxima c" and whether it is the real thing.

    https://www.syfy.com/syfywire/is-thi...ar-maaaaaaaybe
    Last edited by Roger E. Moore; 2020-Apr-16 at 07:51 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

  9. #39
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    New observations of Proxima Centauri say planet b exists, but planet c, if there, is smaller than Earth. What?

    https://arxiv.org/abs/2005.12114
    Revisiting Proxima with ESPRESSO
    A. Suárez Mascareño, et al.
    [Submitted on 25 May 2020]
    We aim to confirm the presence of Proxima b using independent measurements obtained with the new ESPRESSO spectrograph, and refine the planetary parameters taking advantage of its improved precision. We analysed 63 spectroscopic ESPRESSO observations of Proxima taken during 2019. We obtained radial velocity measurements with a typical radial velocity photon noise of 26 cm/s. We ran a joint MCMC analysis on the time series of the radial velocity and full-width half maximum of the cross-correlation function to model the planetary and stellar signals present in the data, applying Gaussian process regression to deal with stellar activity. We confirm the presence of Proxima b independently in the ESPRESSO data. The ESPRESSO data on its own shows Proxima b at a period of 11.218 ±0.029 days, with a minimum mass of 1.29 ±0.13 Me. In the combined dataset we measure a period of 11.18427 ±0.00070 days with a minimum mass of 1.173 ±0.086 Me. We find no evidence of stellar activity as a potential cause for the 11.2 days signal. We find some evidence for the presence of a second short-period signal, at 5.15 days with a semi-amplitude of merely 40 cm/s. If caused by a planetary companion, it would correspond to a minimum mass of 0.29 ±0.08 Me. We find that the FWHM of the CCF can be used as a proxy for the brightness changes and that its gradient with time can be used to successfully detrend the radial velocity data from part of the influence of stellar activity. The activity-induced radial velocity signal in the ESPRESSO data shows a trend in amplitude towards redder wavelengths. Velocities measured using the red end of the spectrograph are less affected by activity, suggesting that the stellar activity is spot-dominated. The data collected excludes the presence of extra companions with masses above 0.6 Me at periods shorter than 50 days.
    Do good work. —Virgil Ivan "Gus" Grissom

  10. #40
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    If Proxima b has continents and oceans, how will that affect its climate and habitability?

    https://arxiv.org/abs/2005.14185
    The Effect of Substellar Continent Size on Ocean Dynamics of Proxima Centauri b
    Andrea M. Salazar, Stephanie L. Olson, Thaddeus D. Komacek, Haynes Stephens, Dorian S. Abbot
    [Submitted on 28 May 2020]
    The potential habitability of tidally locked planets orbiting M-dwarf stars has been widely investigated in recent work, typically with a non-dynamic ocean and without continents. On Earth, ocean dynamics are a primary means of heat and nutrient distribution. Continents are a critical source of nutrients, strongly influence ocean dynamics, and participate in climate regulation. In this work, we investigate how the size of a substellar land mass affects the oceans ability to transport heat and upwell nutrients on the tidally locked planet Proxima Centauri b using the ROCKE-3D coupled ocean-atmosphere General Circulation Model (GCM). We find that dayside ice-free ocean and nutrient delivery to the mixed layer via upwelling are maintained across all continent sizes. We also find that Proxima Centauri ** climate is more sensitive to differences among atmospheric GCMs than to the inclusion of ocean dynamics in ROCKE-3D. Finally, we find that Proxima Centauri b transitions from a lobster state where ocean heat transport distributes heat away from the substellar point to an eyeball state where heat transport is restricted and surface temperature decreases symmetrically from the substellar point when the continent size exceeds about 20 percent of the surface area. Our work suggests that both a dynamic ocean and continents are unlikely to decrease the habitability prospects of nearby tidally locked targets like Proxima Centauri b that could be investigated with future observations by the James Webb Space Telescope (JWST).
    Do good work. —Virgil Ivan "Gus" Grissom

  11. #41
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    Yet another detection of Proxima c, different from the previous ones.

    https://phys.org/news/2020-06-astron...t-proxima.html
    Do good work. —Virgil Ivan "Gus" Grissom

  12. #42
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    Astronomers at McDonald Observatory confirm a second planet, 7x Earth mass, at Proxima Centauri

    https://earthsky.org/space/2nd-exopl...oxima-centauri
    A 2nd exoplanet confirmed for Proxima Centauri
    https://mcdonaldobservatory.org/news/releases/20200602
    2 June 2020
    AUSTIN — Fritz Benedict has used data he took over two decades ago with Hubble Space Telescope to confirm the existence of another planet around the Sun’s nearest neighbor, Proxima Centauri, and to pin down the planet’s orbit and mass. Benedict, an emeritus Senior Research Scientist with McDonald Observatory at The University of Texas at Austin, will present his findings today in a scientific session and then in a press conference at a meeting of the American Astronomical Society.
    Proxima Centauri has been in the news frequently since 2016, when scientists including McDonald Observatory’s Michael Endl found its first planet, Proxima Centauri b. The discovery incited speculation on the types of in-depth studies that could done on an extrasolar planet so close to our own solar system.
    Adding to the excitement, earlier this year a group led by Mario Damasso of Italy’s National Institute for Astrophysics (INAF) announced they might have found another planet orbiting Proxima Centauri farther out. This group used radial velocity observations, that is, measurements of the star’s motion on the sky toward and away from Earth, to deduce the possible planet (dubbed Proxima Centauri c) orbits the star every 1,907 days at distance of 1.5 AU (that is, 1.5 times the distance at which Earth orbits the Sun).
    Do good work. —Virgil Ivan "Gus" Grissom

  13. #43
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    This is getting confusing. Either astronomers are talking about two different planets, both called Proxima c, or someone is wrong, or something. The ESPRESSO data does not match up with this latest information, and other studies do not match up either.
    Do good work. —Virgil Ivan "Gus" Grissom

  14. #44
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    Proxima Centauri's flares are not the only danger to life on Proxima b.

    https://arxiv.org/abs/2006.12503
    [Submitted on 22 Jun 2020]
    Risks for Life on Proxima b from Sterilizing Asteroid Impacts
    Amir Siraj, Abraham Loeb
    We consider the implications that a debris belt located between Proxima b and Proxima c would pose for the rate of large asteroid impacts that could sterilize Proxima b from life. Future observations by ALMA or JWST could constrain the existence of an asteroid belt in the life-threatening regime. We generalize our rate calculation of sterilizing impacts for habitable planets in systems with an asteroid belt and an outer planet.
    Do good work. —Virgil Ivan "Gus" Grissom

  15. #45
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    Proxima Centauri b is unaffected by a powerful magnetic field from its parent star.


    https://arxiv.org/abs/2010.14311

    The large-scale magnetic field of Proxima Centauri near activity maximum

    Baptiste Klein, Jean-François Donati, Élodie M. Hébrard, Bonnie Zaire, Colin P. Folsom, Julien Morin, Xavier Delfosse, Xavier Bonfils

    We report the detection of a large-scale magnetic field at the surface of the slowly-rotating fully-convective M dwarf Proxima Centauri. Ten circular polarization spectra, collected from April to July 2017 with the HARPS-Pol spectropolarimeter, exhibit rotationally-modulated Zeeman signatures suggesting a stellar rotation period of 89.8 ± 4.0 d. Using Zeeman-Doppler Imaging, we invert the circular polarization spectra into a surface distribution of the large-scale magnetic field. We find that Proxima Cen hosts a large-scale magnetic field of typical strength 200 G, whose topology is mainly poloidal, and moderately axisymmetric, featuring, in particular, a dipole component of 135 G tilted at 51∘ to the rotation axis. The large-scale magnetic flux is roughly 3 times smaller than the flux measured from the Zeeman broadening of unpolarized lines, which suggests that the underlying dynamo is efficient at generating a magnetic field at the largest spatial scales. Our observations occur ∼1 yr after the maximum of the reported 7 yr-activity cycle of Proxima Cen, which opens the door for the first long-term study of how the large-scale field evolves with the magnetic cycle in a fully-convective very-low-mass star. Finally, we find that Proxima Cen's habitable zone planet, Proxima-b, is likely orbiting outside the Alfvèn surface, where no direct magnetic star-planet interactions occur.

    ------

    News about Proxima c and candidate planet d.


    https://arxiv.org/abs/2009.07266

    An Earth-like stellar wind environment for Proxima Centauri c

    Julián D. Alvarado-Gómez (1), Jeremy J. Drake (2), Cecilia Garraffo (3 and 2), Ofer Cohen (4), Katja Poppenhäger (1 and 5), Rakesh K. Yadav (3), Sofia P. Moschou (2) ((1) Leibniz Institute for Astrophysics Potsdam, (2) Center for Astrophysics | Harvard & Smithsonian, (3) Harvard University, (4) University of Massachusetts Lowell, (5) University of Potsdam)

    A new planet has been recently discovered around Proxima Centauri. With an orbital separation of ∼1.44 au and a minimum mass of about 7 M⊕, Proxima c is a prime direct imaging target for atmospheric characterization. The latter can only be performed with a good understanding of the space environment of the planet, as multiple processes can have profound effects on the atmospheric structure and evolution. Here, we take one step in this direction by generating physically-realistic numerical simulations of Proxima's stellar wind, coupled to a magnetosphere and ionosphere model around Proxima c. We evaluate their expected variation due to the magnetic cycle of the host star, as well as for plausible inclination angles for the exoplanet orbit. Our results indicate stellar wind dynamic pressures comparable to present-day Earth, with a slight increase (by a factor of 2) during high activity periods of the star. A relatively weak interplanetary magnetic field at the distance of Proxima c leads to negligible stellar wind Joule heating of the upper atmosphere (about 10% of the solar wind contribution on Earth) for an Earth-like planetary magnetic field (0.3 G). Finally, we provide an assessment of the likely extreme conditions experienced by the exoplanet candidate Proxima d, tentatively located at 0.029 au with a minimum mass of 0.29 M⊕.

    -----

    News on Proxima itself.


    https://arxiv.org/abs/2008.07175

    Proxima Centauri -- the nearest planet host observed simultaneously with AstroSat, Chandra and HST

    S. Lalitha, J.H.M.M. Schmitt, K.P. Singh, P. C. Schneider, R. O. Parke Loyd, K. France, P. Predehl, V. Burwitz, J. Robrade

    Our nearest stellar neighbour, Proxima Centauri, is a low mass star with spectral type dM5.5 and hosting an Earth-like planet orbiting within its habitable zone. However, the habitability of the planet depends on the high-energy radiation of the chromo-spheric and coronal activity of the host star. We report the Astrosat, Chandra and HST observation of Proxima Centauri carried out as part of the multi-wavelength simultaneous observational campaign. Using the soft X-ray data, we probe the different activity states of the star. We investigate the coronal temperatures, emission measures and abundance. Finally, we compare our results with earlier observations of Proxima Centauri.
    Do good work. —Virgil Ivan "Gus" Grissom

  16. #46
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    Proxima b interacts with its sun, Proxima Centauri, to produce radio emissions we can detect.

    https://arxiv.org/abs/2012.02116

    Monitoring the radio emission of Proxima Centauri

    Miguel Pérez-Torres, José Francisco Gómez, José Luis Ortiz, Paolo Leto, Guillem Anglada, José Luis Gómez, Eloy Rodríguez, Corrado Trigilio, Antonio Alberdi, Guillem Anglada-Escudé, Mayra Osorio, Grazia Umana, Zaira Berdiñas, María José López-González, Nicolás Morales, Cristina Rodríguez-López, James Chibueze

    We present results from the most comprehensive radio monitoring campaign towards the closest star to our Sun, Proxima Centauri. We report 1.1 to 3.1 GHz observations with the Australian Telescope Compact Array over 18 consecutive days in April 2017. We detect radio emission from Proxima Centauri for most of the observing sessions, which spanned ∼1.6 orbital periods of the planet Proxima b. The radio emission is stronger at the low-frequency band, centered around 1.6 GHz, and is consistent with the expected electron-cyclotron frequency for the known star's magnetic field intensity of about 600 Gauss. The 1.6 GHz light curve shows an emission pattern that is consistent with the orbital period of the planet Proxima b around the star Proxima, with its maxima of emission happening near the quadratures. We also observed two short-duration (a few minutes) flares and a long-duration (about three days) burst whose peaks happened close to the quadratures. We find that the frequency, large degree of circular polarization, change of the sign of circular polarization, and intensity of the observed radio emission are all consistent with expectations from electron cyclotron-maser emission arising from sub-Alfvénic star-planet interaction. We interpret our radio observations as signatures of interaction between the planet Proxima b and its host star Proxima. We advocate for monitoring other dwarf stars with planets to eventually reveal periodic radio emission due to star-planet interaction, thus opening a new avenue for exoplanet hunting and the study of a new field of exoplanet-star plasma interaction.
    Do good work. —Virgil Ivan "Gus" Grissom

  17. #47
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    Proxima Centauri had a unique type of flare event, with meaning for its planets.

    https://arxiv.org/abs/2012.04642

    A Flare-Type IV Burst Event from Proxima Centauri and Implications for Space Weather

    Andrew Zic, Tara Murphy, Christene Lynch, George Heald, Emil Lenc, David L. Kaplan, Iver H. Cairns, David Coward, Bruce Gendre, Helen Johnston, Meredith MacGregor, Danny C. Price, Michael S. Wheatland

    Studies of solar radio bursts play an important role in understanding the dynamics and acceleration processes behind solar space weather events, and the influence of solar magnetic activity on solar system planets. Similar low-frequency bursts detected from active M-dwarfs are expected to probe their space weather environments and therefore the habitability of their planetary companions. Active M-dwarfs produce frequent, powerful flares which, along with radio emission, reveal conditions within their atmospheres. However, to date, only one candidate solar-like coherent radio burst has been identified from these stars, preventing robust observational constraints on their space weather environment. During simultaneous optical and radio monitoring of the nearby dM5.5e star Proxima Centauri, we detected a bright, long-duration optical flare, accompanied by a series of intense, coherent radio bursts. These detections include the first example of an interferometrically detected coherent stellar radio burst temporally coincident with a flare, strongly indicating a causal relationship between these transient events. The polarization and temporal structure of the trailing long-duration burst enable us to identify it as a type IV burst. This represents the most compelling detection of a solar-like radio burst from another star to date. Solar type IV bursts are strongly associated with space weather events such as coronal mass ejections and solar energetic particle events, suggesting that stellar type IV bursts may be used as a tracer of stellar coronal mass ejections. We discuss the implications of this event for the occurrence of coronal mass ejections from Proxima Cen and other active M-dwarfs.
    Do good work. —Virgil Ivan "Gus" Grissom

  18. #48
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    Quote Originally Posted by Roger E. Moore View Post
    Proxima Centauri had a unique type of flare event, with meaning for its planets.

    https://arxiv.org/abs/2012.04642

    A Flare-Type IV Burst Event from Proxima Centauri and Implications for Space Weather

    Andrew Zic, Tara Murphy, Christene Lynch, George Heald, Emil Lenc, David L. Kaplan, Iver H. Cairns, David Coward, Bruce Gendre, Helen Johnston, Meredith MacGregor, Danny C. Price, Michael S. Wheatland

    Studies of solar radio bursts play an important role in understanding the dynamics and acceleration processes behind solar space weather events, and the influence of solar magnetic activity on solar system planets. Similar low-frequency bursts detected from active M-dwarfs are expected to probe their space weather environments and therefore the habitability of their planetary companions. Active M-dwarfs produce frequent, powerful flares which, along with radio emission, reveal conditions within their atmospheres. However, to date, only one candidate solar-like coherent radio burst has been identified from these stars, preventing robust observational constraints on their space weather environment. During simultaneous optical and radio monitoring of the nearby dM5.5e star Proxima Centauri, we detected a bright, long-duration optical flare, accompanied by a series of intense, coherent radio bursts. These detections include the first example of an interferometrically detected coherent stellar radio burst temporally coincident with a flare, strongly indicating a causal relationship between these transient events. The polarization and temporal structure of the trailing long-duration burst enable us to identify it as a type IV burst. This represents the most compelling detection of a solar-like radio burst from another star to date. Solar type IV bursts are strongly associated with space weather events such as coronal mass ejections and solar energetic particle events, suggesting that stellar type IV bursts may be used as a tracer of stellar coronal mass ejections. We discuss the implications of this event for the occurrence of coronal mass ejections from Proxima Cen and other active M-dwarfs.
    More on the discovery of new flare types at Proxima Centauri. The news is bad for planetary life there.

    QUOTE: A discovery that links stellar flares with radio-burst signatures will make it easier for astronomers to detect space weather around nearby stars outside the Solar System. Unfortunately, the first weather reports from our nearest neighbour, Proxima Centauri, are not promising for finding life as we know it. ... "But given Proxima Centauri is a cool, small red-dwarf star, it means this habitable zone is very close to the star; much closer in than Mercury is to our Sun," he said. "What our research shows is that this makes the planets very vulnerable to dangerous ionising radiation that could effectively sterilise the planets."

    https://phys.org/news/2020-12-space-...e-planets.html
    https://scitechdaily.com/stellar-fla...anets-at-risk/
    Last edited by Roger E. Moore; 2020-Dec-09 at 06:31 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

  19. #49
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    Do good work. —Virgil Ivan "Gus" Grissom

  20. #50
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    Quote Originally Posted by Roger E. Moore View Post
    Signal probably of human origin, not aliens.

    https://www.syfy.com/syfywire/a-sign...ly-from-aliens
    Do good work. —Virgil Ivan "Gus" Grissom

  21. #51
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    The Proxima Centauri signal, at 982.002 MegaHertz is *very* nearly three times that of the deuterium spectral line (327.384 MHz), which is well known to radio astronomers. This could be a coincidence, of course, but the fit is very close. Such a correspondence looks a good deal like an example of the 'magic frequency' logic used in SETI circles.

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