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July 16th, 2006

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We’re working hard to keep the systemic project moving forward.

Eugenio, as of July 14th, has compiled and documented all of the published radial velocity data sets, and has been designing and developing the “KeckTAC” code, which will be a workhorse for systemic’s next phase. The published datasets are all available on the systemic systems catalog. Aaron has stripped the console down to its component parts, and he’s rebuilding it with new features, faster algorithms and a sleekly expandable architecture. Stefano has been tweaking the systemic backend [sign up and get fittin', y'all -ed.], and will be arriving at UCSC in the Fall to do his Ph.D. research. We’re hoping that part of his thesis will be a statistical analysis of the final results of the 100,000 star systemic simulation.

When I was in graduate school, I spent a lot of time doing research on brown dwarfs (objects between 13 and 75 Jupiter masses that lie in the mass range between giant planets and red dwarf stars). At that time, circa 1992, no bona-fide brown dwarfs had actually been found, but the prospects for detecting them seemed reasonably good. My friend Todd Henry, who was a graduate student at the University of Arizona, and who was hunting for brown dwarfs using the speckle method, told me something that stuck in my mind.

“Face it, Greg,” he said, “the reason you’re interested in brown dwarfs is not because you’re interested in Brown Dwarfs — the reason you’re interested in brown dwarfs is because you’re really interested in planets, and brown dwarfs are just one stop away on the line.”

He was right.

A similar logic might apply today, “The reason I’m interested in giant planets is not because I’m really interested in Giant Planets — the reason I’m interested in giant planets is because I’m really interested in habitable terrestrial planets, and giant planets are one stop away on the line.”

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  1. July 16th, 2006 at 21:06 | #1

    Before “habitable terrestrial planets”, we are looking for (hot) super-terrestrial planets, then “small” terrestrial planets etc…

  2. qraal
    July 16th, 2006 at 21:41 | #2

    Follow the Yellow Brick Road…

  3. Eugenio
    July 16th, 2006 at 21:42 | #3

    Hi All,

    Here is the revised list of systems which are not yet on the console (5) because the radial velocity data is missing or it exists in a phased form only: HD122430, HD196885, HD34445, HD59686, and HD73256. At some point this week, I’ll try to include velocities for HD41004A (and possibly B) and Alpha Cen A and B.


  4. qraal
    July 16th, 2006 at 21:44 | #4

    Real live terrestrials with real live extra-terrestrials… Oz, by another name. Of course we may not find any habitable planets nearby. Michael Hart’s old models had habitable planets around one in every 250,000 stars or so. We might be faced with similarly long odds.

  5. greg
    July 16th, 2006 at 23:52 | #5

    One in 250,000 sounds way too conservative for _Earth-mass_ planets in the habitable zone. My guess is that such worlds are 50,000 times more common than that. I would not be surprised, however, if a ~1-bar atmosphere, liquid water, and all the other “mod cons” do wind up pushing the number of habitable planets down to 1 in 250,000 stars. We’ve got plenty of planets in our solar system, and nothing other than the Earth is even remotely habitable — including Mars. [Although I'm holding out for an early ocean and an interesting prior history on Venus.]

  6. qraal
    July 17th, 2006 at 13:22 | #6

    What’s your best guess on ‘stars with planets’? Should we expect them all to have planets, or is the latest work on planet formation in low metallicity nebulas making that idea harder to uphold?

    I agree terrestrials seem likely to be common, but I’m really wondering what absent Jupiter mass planets will mean for terrestrials. Do simulations produce large terrestrial planets in systems lacking Jovians? Or does the disk just scatter when the planetesimals hit the moon-mass stage?

  7. andy
    July 17th, 2006 at 15:00 | #7

    What’s the chances that most terrestrial planets with semimajor axes in the habitable zone are going to be on highly eccentric orbits?

    Hmmm… a habitable world in the eccentric resonance could be interesting…

  8. greg
    July 17th, 2006 at 19:26 | #8

    My thinking is that most stars in the galactic disk should have planetary systems, with the default configuration being a terrestrial planetary system containing 3-5 rocky planets (totaling slightly less mass than MVEMM) and one or two Neptune-mass ice giants further out. Simulations done by John Chambers and others indicate that terrestrial planet formation is not too different when one has a Neptune-mass core doing the perturbing rather than a full-blown Jupiter-Saturn pair. Even when there are no giant planets, you generally end up with Mars-sized, rather than Moon-sized final bodies. I think that you have to get down to really metal poor halo-type stellar populations before you see terrestrial planets becoming scarce. (Note that three out of four of the solar system’s outer planets managed to wind up with regular satellite systems.)

    I think most terrestrial planets will wind up having moderate to low eccentricities, but there will certainly be many examples of highly eccentric orbits and complicated resonant configurations. Kepler and Corot will give us some indication of whether the terrestrial exo-planets tend to be on highly eccentric orbits (to the extent that we can get accurate mass and radius measurements for the parent stars).


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