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 11-01-2010, 04:32 AM #11 Phantasm     Join Date: Jun 2006 Location: On the road again... Re: [Space] Alpha Centauri example stats What are the odds, based on this spreadsheet, of both Alpha Centauri A (G2) and Alpha Centauri B (K7, IIRC) having a habitable planet and/or moon? (I'm discounting Proxima as improbable for a habitable world, due to it being a red dwarf with a "comfort zone" that can be scorched by random flares on a regular basis.) __________________ "Life ... is an Oreo cookie." - J'onn J'onzz, 1991 "But mom, I don't wanna go back in the dungeon!" The GURPS Marvel Universe Reboot Project A-M and N-Z, and its not-a-wiki-really web adaptation. Ranoc, a Muskets-and-Magery Renaissance Fantasy Setting
11-01-2010, 04:53 AM   #12
Agemegos

Join Date: May 2005
Location: Oz
Re: [Space] Alpha Centauri example stats

Quote:
 Originally Posted by tbrock1031 What are the odds, based on this spreadsheet, of both Alpha Centauri A (G2) and Alpha Centauri B (K7, IIRC) having a habitable planet and/or moon?
I got 538 systems meeting that criterion out of 100,000 instances, or 5.38%. I think that means that the 95% confidence interval for the true probability is 4.94%–5.82%.

Mind you, in doing that exercise I had to fudge between the given masses, spectral classes, and luminosities of the stars in Alpha Centauri. The system is reckoned as 6.552 Ga old, and A is observed to have mass 1.1, type G2 V, luminosity 1.567. But GURPS Space says that a star of mass 1.1 will be a G0, and that at age 6.552 Ga its luminosity will be 2.2. I compromised on a mass of 1.09 to get the luminosity about right (which with the mass about right put the planets in about the right orbits), accepting a spectral type of G1 V instead of G2 V. B is observed to have mass 0.85, type K4 V, luminosity 0.46, but Space gives type G8 V, luminosity 0.54 on that mass and age. I fudged the mass down to 0.84 and got a compromise type K0V, luminosity 0.4.

To get an accurate model of Alpha Centaauri I would have to hack the bit of the workbook that implements GURPS Space's model relating a star's mass and age to its type and luminosity. That wouldn't take long or be difficult—for me—but it didn't do it because my point was to demonstrate the use of my star system generator.
Quote:
 (I'm discounting Proxima as improbable for a habitable world, due to it being a red dwarf with a "comfort zone" that can be scorched by random flares on a regular basis.)
That's a good point. Proxima is an x-ray-flare star, very nasty. I should discount those 100 instances in which the star system generation sequence gave it a habitable planet.
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Last edited by Agemegos; 11-01-2010 at 07:42 PM. Reason: added a note

 Tags alpha centauri, space, system generation

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