Earth-sized exoplanet spotted in star’s habitable zone

  1. reenmachine

    reenmachine 525
    Gold Member

    Last edited: Apr 17, 2014
  2. jcsd
  3. mfb

    Staff: Mentor

    As the nasa website is very unreliable (at least for me)*:

    *edit, clarification: I cannot reach the website sometimes due to DNS server issues. This is a technical issue and has nothing to with the content.
    Last edited: Apr 23, 2014
  4. Drakkith

    Staff: Mentor

  5. Greg Bernhardt

    Staff: Admin

    How easily can the composition be known if at all? I suppose that is the next great signal.
  6. They are saying even after the James Webb comes online, it might not be able to get a good read on this planet because the star could be too dim.
  7. mfb

    Staff: Mentor

    Then we can still hope for the E-ELT.
    Even if not, it is just a matter of time until we can do this, PLATO will launch in ~10 years, it should find a lot of those planets at stars closer to our own.
  8. very exciting times.
  9. Kepler-186f does not reside in the habitable zone of its star.

    The habitable zone can be calculated for any star. If you know the luminosity of the star then it is merely a simple calculation:
    ri = √ (Star's Luminosity / 1.1)
    ro = √ (Star's Luminosity / 0.53)​
    According to the paper where the discovery was announced the luminosity of the Kepler-186 M1V star is 0.0412. Which puts the habitable zone of the star at between 0.19353 AU and 0.27881 AU. Yet the paper places the semi-major axis of the planet at 0.3926 AU. Well outside the habitable zone of the star.

    Formation, Tidal Evolution & Habitability of the Kepler-186 System - arVix 1404.4368v1 [PDF]
    Calculating the Habitable Zone
  10. Does it have an elliptical orbit that puts it within the habitable zone at any point?
  11. mfb

    Staff: Mentor

    The units do not fit (they do fit in the source, however), and the numerical constant of 0.53 would indicate a precision the current models do not have.

    I guess that would make things even worse due to extreme seasonal variations (together with issues like the long-term stability of the orbit) - and the average would still be similar.
  12. Possibly. All they can say is that Kelper-186f has an eccentricity of less than 0.34. So it might fall within the habitable zone for a time, or it may never fall in the habitable zone.
  13. What do you mean "the units do not fit?" I am using their data from their paper, and the planet does not fall within the habitable zone of the star. Not by a long shot. Despite their claims to the contrary. Apparently they are more interested in publicity than actual science.
  14. mfb

    Staff: Mentor

    r is a length and needs a unit of length (like meters or AU), unless you specify something like "in meters" or (here) "in AU". The same applies to the luminosity.
    The claim comes from the Kepler collaboration and they are certainly interested in actual science. That leaves multiple possible options:
    - error from Kepler
    - error from Tom E. Morris (or the sources he bases his formulas on)
    - error from you combining both
    - error in our interpretation, as an example the definition of "habitable zone" varies a bit between different scientists
    - something else (there is always something else)
  15. As I previously posted, ri and ro is in AU.
    I am using only the data the discoverer's provided in their paper. I am not taking any other source. There are actually several different sources for Kelper-186 and Kepler-186f, and they do not all have the same data in common. Which is why I specifically chose to use their source paper and their data.

    If they want to redefine the size of a habitable zone around a star, fine. But at the very least they could have explained why in this particular case they are expanding it to include this exoplanet. It should not be expanded merely because they want to be the first to find an Earth-like exoplanet. They call that sensationalism, not science.

    When you find an error in my math, then you can rightly blame me. However, if my math is correct and I provided the sources for both the calculations and the data, then I am hardly to blame. Your hostility towards me is misplaced.
  16. The distance from the star alone may not exclude it from habitability. depending on the composition of the atmosphere. if it has a very thick CO2 atmosphere it could still maintain suitable temperatures for plant life. Being further away from its star might also be a benefit as it might not be tially locked.
  17. mfb

    Staff: Mentor

    I don't get the original publication to load here, but I assume the wikipedia editors managed to copy the numbers correctly:
    => different definition of "habitable zone".
  18. Bandersnatch

    Bandersnatch 1,571
    Science Advisor
    Gold Member

    Using this calculator:
    and accompanying paper(Kopparapu et al.):
    For a 3500K, 0.0412 solar luminosity star you get the conservative habitable zone between 0.22 and 0.41 AU.

    The above calculation method is mentioned and linked to in the second link you provided(near the bottom) as an "alternative approach". Judging from the numbers mfb dug up, it is clear that it was the method used.
    1 person likes this.
  19. 1 person likes this.
  20. good article, thanks.
  21. Unfortunately I could not get their calculator to work properly. Every time I entered the values for the star's surface temperature and the star's luminosity, it kept getting reset to Sol's values. However, I am in the process of reading the paper "Habitable Zones Around Main-Sequence Stars: New Estimates." Thanks.
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