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Featured B A terrestrial, temperate planet around Proxima Centauri

  1. Aug 24, 2016 #1


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    Published today in Nature:
    Anglada-Escudé et al. (2016) A terrestrial planet candidate in a temperate orbit around Proxima Centauri. Nature: 536: 437. doi:10.1038/nature19106

    Popular press summary: http://www.nature.com/news/earth-si...rby-star-is-astronomy-dream-come-true-1.20445

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  3. Aug 24, 2016 #2


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    The main problem is the 11 day orbit which means that it's probably tidally locked and the tendancy of red dwarfs to flare which would mean lots of radiation. Probably not a nice place to visit.
  4. Aug 24, 2016 #3
  5. Aug 24, 2016 #4
    For us, yes, but I don't think this damages the prospect of life-- a quality of all living species is the ability to adapt.
  6. Aug 24, 2016 #5


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    According to the paper, x-ray fluxes on Proxima b are 400 times as high as they are on Earth. However, organisms have been found near Chernobyl that thrive in environments with radiation levels 500 times higher than normal (https://en.wikipedia.org/wiki/Radiotrophic_fungus), so radiation levels on Proxima b would not necessarily preclude the possibility of life.
  7. Aug 24, 2016 #6
    However, being tidally locked means that only a small part of the planet would have conditions in which life might conceivably get started.
    About 80% of the surface it would be either permanently arid desert on the sun side or permanent ice desert on the far side.
  8. Aug 24, 2016 #7
    Heat distribution to the dark side is possible if the planet still has an atmosphere capable of resisting the flares.

    Protective magnetic field is also a possibility.
  9. Aug 24, 2016 #8
    Related question-- will we have to wait another 8.4 years to find out if there is life, and to find out the answers to the other questions we have, such as if it has an atmosphere?
  10. Aug 24, 2016 #9
    That would only be applicable of we intended to send a probe there, (and at lightspeed).
    It's possible that we could get signatures of molecules and other phenomena indicating life just from next generation telescopes and other technologies.
    In astromomical terms it's so close it like being just outside the front door of our house.
  11. Aug 24, 2016 #10
    Or sent some form of light that would give us a better look, like a radar.
  12. Aug 24, 2016 #11
    I guess in principle something similar to radar could be used to do terrain mapping, and from this we might be able to draw a few indirect conclusions regarding life.
    I don't think there is any such technology with that sort of resolution anywhere near available in the near future.
    If it was available though, then yes we wouldn't get any return signal for over eight years.
    Last edited: Aug 24, 2016
  13. Aug 24, 2016 #12
    No space imaging technology is based on the premise of sending a signal to a target and analyze it's bounce back. It's unnecessary and not really practical for objects that are light-years away.

    We can simply analyze the light received from an object. The problem is that imaging exoplanets is very tricky given their dim light compared to the host stars. There are techniques to derive chemical signatures from the light radiated (or reflected) by an atmosphere. If Proxima b has an atmosphere we might be able to detect it through infrared spectroscopy if it transits the red dwarf. With UV or X-ray imaging, we may be able to determine whether there's a magnetic field or not (by tracking potential deflections of the red dwarf's 'solar storms', I think).

    Direct imaging is a pain with exoplanets, especially in visible light. James Web will scan the infrared spectrum within two years, but with an angular resolution practically identical to the Hubble.

    EDIT: We'd probably have to send probes to find evidence of life. Project Starshot kind of thing.
    Last edited: Aug 24, 2016
  14. Aug 25, 2016 #13


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  15. Aug 25, 2016 #14
    Just curious, this planet is called "proxima b." Is there a "proxima a"? Is that another planet? Or is "proxima a" the star itself?
  16. Aug 25, 2016 #15
    It's the star itself.
  17. Aug 25, 2016 #16
    We've identified water, methane, oxygen and other molecules in atmospheres of hot Jupiters, but not (as far as I know) for smaller planets. It is determined from the starlight passing through the planetary atmospheres during transits.

    I've heard the argument that life is the only mechanism that will produce a significant component in a planetary atmosphere, so if we find someplace that is more than about 15% oxygen, it is a strong indicator of life.
  18. Aug 25, 2016 #17
    Finding free Oxygen would certainly be a primary indicator of life, but life can also exist in a low oxygen atmosphere.
    It's thought that the earliest life on Earth existed in a low oxygen environment, then later some simple lifeform hit upon photosynthesis.
    (and that resulting free O2 inserted to the atmosphere was actually poison as far as a lot of the other early microbes were concerned - apparently most of them went extinct within a geologically fairly short time )
    Last edited: Aug 25, 2016
  19. Aug 25, 2016 #18
    I've found: X-Ray attenuation & absorption calculator, something that uses NIST: X-Ray Mass Attenuation Coefficients. In particular, I've found NIST: X-Ray Mass Attenuation Coefficients - Air, Dry. That attenuation coefficient is given as cm^2/g, and one multiplies it by the material's column density in g/cm^2 to give the optical depth. Our atmosphere has a column density of about 1034 g/cm^2.

    The smallest mass attenuation coefficient in that table is 0.018 cm^2/g for 100 MeV, giving an optical depth of 18. At 1 MeV, it is about 0.1 cm^2/g, giving an optical depth of 100, and for lower energies, it is even higher.

    For N2, O2, and CO2, it is not much different.

    So Proxima b's atmosphere will easily absorb Proxima's X-rays unless it is as thin as Mars's atmosphere or thinner.
  20. Aug 25, 2016 #19
    How old is Proxima Centauri?
  21. Aug 25, 2016 #20
    Wikipedia has a good article on Proxima Centauri. Almost anything you'd like to know about it is there.

    This is wrong, by the way. Launch is scheduled for October 2018, so more like three years.
    Last edited: Aug 25, 2016
  22. Aug 25, 2016 #21
    I'd heard the argument from a geochemist a few years back that once a planet is tidally locked, the dark side cools so much that the atmosphere will solidify and be lost over a shorter time span that it would likely take like to start.

    Just looking it up know I find some reports of modelling indicate this will not happen in all cases, and others show that even water might not entirely freeze. This search also led me to a paper that concludes the presence of an atmosphere can prevent tidal locking, although the reasoning for that is not entirely clear to me...I think I need to review the specifics of becoming locked in the first place.
  23. Aug 26, 2016 #22


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    This eprint today suggests even a thin atmosphere is sufficient to prevent this happening to Proxima b: Tutorial models of the climate and habitability of Proxima Centauri b: a thin atmosphere is sufficient to distribute heat given low stellar flux.

    Last edited: Aug 26, 2016
  24. Aug 29, 2016 #23


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    More on the James Webb telescope and observing the planet: Prospects for Characterizing the Atmosphere of Proxima Centauri b.

  25. Aug 30, 2016 #24
    I wanted to know why this planet had not been found before. Kepler and other telescopes have found planets on stars much further away, and giving Proxima's status as the nearest star, I imagine it was the first one they pointed the telescopes towards. What stopped this planet from having been found on previous passes?
  26. Aug 30, 2016 #25
    Most of planets discovered by Kepler and other telescopes in the earliest stages were very big and obvious, Jupiter sized and bigger.
    The smaller planets in most cases started to reveal themselves only after several times of reprocessing the data.
    Quite a lot of the early results turned out to be false positives when rechecked
    The teams working on this would not want to make a press release until they had a high level of confidence.

    Remember this is not normal optical telescope photography, exoplanets are detected by statistically analysing variations in the light received from the parent star.
    Last edited: Aug 30, 2016
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