Results 1 to 10 of 10

Thread: HR diagram for planets

  1. #1
    Join Date
    Nov 2004
    Posts
    5,413

    HR diagram for planets

    If we were to make one, what would its parameters be? What sort of things would it be designed to reveal? We arguably have enough data to construct one now, but I'm not sure what properties to plot that could reveal meaningful information.
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

  2. #2
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    21,728
    Whatever the diagram would be, it wouldn't be enough like the HR diagram to call it an HR diagram.
    We don't have much data on exoplanets, and almost all of the data we do have so far highly biased toward what is easily observed (big planets, short orbits, orbits aligned with our POV).
    I could imagine creating a diagram showing some exoplanet parameter such as size, vs. the metallicity of the host star, to see details about that relationship.
    Forming opinions as we speak

  3. #3
    Join Date
    Apr 2005
    Posts
    2,246
    "Planet occurrence is flat against Log(Period)" is one phrase I remember. Don't know if it is still supported by recent data.

    There are all kinds of other plots with metallicity and size versus period available out there in the literature.

  4. #4
    Join Date
    Sep 2003
    Location
    The beautiful north coast (Ohio)
    Posts
    47,144
    There are the plots in this paper of exoplanet mass and exoplanet radius as a function of orbital period, for example.

    As others have said, I don't see two or three parameters as enough to describe exoplanets.
    At night the stars put on a show for free (Carole King)

    All moderation in purple - The rules

  5. #5
    Join Date
    Nov 2010
    Posts
    240
    If I correctly understand the nature of HR diagrams they are not only a snapshot of the distribution of stars in terms of luminosity versus surface temperature, but can also portray the path followed by a star from formation to death. In that regard exoplanets are quite different: they form through accretion and once that violence is over very little in the way of gross change occurs thereafter.

    What the OP may be asking is, "what sort of scatter plots would help us to visualise a useful classification of exoplanets?" In that case, I suggest mass versus composition would might work. Since we have no way, currently, of determining composition we might consider using density as a proxy for this. I wold hope this would let us distinguish gas giant, ice giants and terrestrials. A 3-D cross plot, with the additional axis of stellar metallicity (as suggested by another member) could be interesting.

  6. #6
    Join Date
    Nov 2004
    Posts
    5,413
    Quote Originally Posted by Eclogite View Post
    What the OP may be asking is, "what sort of scatter plots would help us to visualise a useful classification of exoplanets?" In that case, I suggest mass versus composition would might work. Since we have no way, currently, of determining composition we might consider using density as a proxy for this. I wold hope this would let us distinguish gas giant, ice giants and terrestrials. A 3-D cross plot, with the additional axis of stellar metallicity (as suggested by another member) could be interesting.
    I think that might be what I'm asking, yes, though the HR diagram actually revealed something fundamental about the nature of stars. There are hints of something beginning to stir in the Kepler data; for instance, it seems that Earth-like planets are more common than Jupiter-sized planets, and Neptune-sized planets are more common than Earth-sized planets.
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

  7. #7
    Join Date
    Sep 2006
    Posts
    1,760
    Anyone interested in making diagrams of this sort can go to NASA Exoplanet Data Archive and make them in a snap:

    https://exoplanetarchive.ipac.caltec...config=planets

  8. #8
    Join Date
    Oct 2005
    Posts
    26,057
    This would be my vote for the closest equivalent: https://en.wikipedia.org/wiki/Exopla...s-20170616.png
    As with the H-R diagram, one gets a sense of the basic things we care about the planet by its location in the plot. There is even a sense of evolutionary tracks, because hot Jupiters have to have migrated in from farther out. However, there is a conspicuous absence of a "main sequence", so the plot is not useful for simplifying the dizzying number of contributing parameters.

  9. #9
    Join Date
    Sep 2003
    Posts
    12,142
    Quote Originally Posted by Ken G View Post
    This would be my vote for the closest equivalent: https://en.wikipedia.org/wiki/Exopla...s-20170616.png
    As with the H-R diagram, one gets a sense of the basic things we care about the planet by its location in the plot. There is even a sense of evolutionary tracks, because hot Jupiters have to have migrated in from farther out. However, there is a conspicuous absence of a "main sequence", so the plot is not useful for simplifying the dizzying number of contributing parameters.
    Add a z-axis for host luminosity and it would be extra nice, and more H-R-y.
    We know time flies, we just can't see its wings.

  10. #10
    Join Date
    Oct 2005
    Posts
    26,057
    If you want to get habitability into it, since that's a key issue, I'd just scale the orbital period on the x axis to the period at the center of the habitability zone. The only reason to use an unscaled period is empirical considerations like telling which planets Kepler would work for, etc.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •