Comments on: extraterrestrial http://oklo.org/2006/07/16/extraterrestrial/ characterizing planetary systems Fri, 18 Nov 2011 22:27:52 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: greg http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-223 greg Mon, 17 Jul 2006 19:26:07 +0000 http://oklo.org/?p=110#comment-223 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). best, Greg 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).

best,
Greg

]]> By: andy http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-222 andy Mon, 17 Jul 2006 15:00:32 +0000 http://oklo.org/?p=110#comment-222 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... 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…

]]> By: qraal http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-220 qraal Mon, 17 Jul 2006 13:22:33 +0000 http://oklo.org/?p=110#comment-220 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? 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?

]]> By: greg http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-218 greg Sun, 16 Jul 2006 23:52:09 +0000 http://oklo.org/?p=110#comment-218 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.] 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.]

]]> By: qraal http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-217 qraal Sun, 16 Jul 2006 21:44:24 +0000 http://oklo.org/?p=110#comment-217 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. 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.

]]> By: Eugenio http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-216 Eugenio Sun, 16 Jul 2006 21:42:01 +0000 http://oklo.org/?p=110#comment-216 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. Eugenio 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.

Eugenio

]]> By: qraal http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-215 qraal Sun, 16 Jul 2006 21:41:05 +0000 http://oklo.org/?p=110#comment-215 Follow the Yellow Brick Road... Follow the Yellow Brick Road…

]]> By: Vincent http://oklo.org/2006/07/16/extraterrestrial/comment-page-1/#comment-214 Vincent Sun, 16 Jul 2006 21:06:52 +0000 http://oklo.org/?p=110#comment-214 Before "habitable terrestrial planets", we are looking for (hot) super-terrestrial planets, then "small" terrestrial planets etc... :-D Before “habitable terrestrial planets”, we are looking for (hot) super-terrestrial planets, then “small” terrestrial planets etc…
:-D

]]>