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Planets for Humanity






Rich & Ancient Star Systems

  • Metal-Poor Star Systems
  • Metal-Rich and Ancient Star Systems
  • Table of Ancient and Metal-Rich Star Systems
  • Sky Map Locations of Selected Ancient, Rich Stars
  • PRE-REQUISITES
    FOR HABITABLE PLANETS
    Two pre-requisites for habitable planets involve the age and chemistry of their parent star. Though the Dole-Asimov book, Planets for Man, spoke at great length about stellar age as an important consideration, very little was known about the ages of individual stars back in the 1960's. For most of the twentieth century, only the maximum possible age for a lone star could be stated with any certainty. With the techniques used then, a star like our sun might be an infant or poised on the brink of old age. There was no way to know.

    Today's techniques allow us to gauge the approximate age of hundreds of individual stars. Stars with the right age and the right chemistry are prime candidates for our search. Below is a list of stars that exceed these two pre-requisites. But first let's take a look at why these are pre-requisites in the first place.

    INFANT STAR SYSTEMS
    Too young a star system (~2 billion years or less) would still be in its formative stages. Planets would still be suffering the bombardment of large meteoric material. If life were to start on such a world, there exists a very real danger that one large meteor would destroy that life, much as one is theorized to have done in destroying the dinosaurs on Earth.

    IMPORTANCE OF STELLAR AGE TO PLANETARY LIFE
    Based on the admittedly small sample of one, the development of life on our planet might be used as a rough measure for that in other star systems. The timeline chart, below, shows many of the significant events in the progress of life on Earth. It wasn't until long after the major bombardments had stopped that Earth's atmosphere gained a significant amount of oxygen. During the Mesozoic era (green), the dinosaurs emerged and lived. And the Cenozoic saw the rise of mammals to dominance. Based on the Earth model, a star system younger than 2.5 billion years would likely not have any habitable worlds.



    METAL-POOR STAR SYSTEMS
    A star system too poor in heavier elements would likely not have planets, or the planets would be made largely of hydrogen and possibly water. No Earth-like world is likely to be found in such a system. Throughout our galaxy, and surrounding it in what is called the galactic "halo," are stars that are extremely old, but very poor in heavier elements. After all, the earliest stars were made of pure hydrogen; the heavier elements came later, with the death of the first giants. One such "halo" intruder to the galactic disk is the star, Arcturus, in the constellation Bootes. The globular clusters orbiting our galaxy are also metal deficient, yet are thought to contain some of the oldest stars in the universe. Based on more recent studies, it may well prove that all of these metal-poor systems are devoid of planets.

    METAL-RICH AND ANCIENT STAR SYSTEMS
    The following list is by no means complete. This is but a sampling of stars within and near the Solar neighborhood. Each star is rich with heavier elements, and old enough to have mature, life-bearing planets. In fact, all of these stars are thought to be at least as old as our own sun — some far older. If any of these systems have a habitable world, and if life developed there in a sequence similar to that on Earth, there exists the possibility that such a planet would harbor a civilization far more ancient than ours.

    For more information on the meanings of the column headings, simply click the appropriate heading. For more information on a specific star, click on the HD number for that star. Distances are in parsecs. "Low," "Age," and "High" give a range of star ages, from low, to nominal and finally high estimates (in giga-years).



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    Selected Rich and Ancient Star Systems

    HIP # HD # Cmp Name (constellation) SpType Dist VMag FeH Low Age High Closeup
    71683 128620 ABC Alpha Centauri G2 V 1 -0.01 0.15   8.17   Star
    3093 3651 AB 54 Piscium   [planet found] K0 V 11 6.10 0.19 2.60 17.00    
    58576 104304   BD -09° 3413 (Virgo) K0 IV-V 13 5.60 0.25 7.70 16.30    
    77358 140901 ABC CD -37° 10500 (Lupus) G6 V 15 6.10 0.05 3.70 13.70    
    93858 177565   CD -37° 13049 (Crater) G5 IV-V 17 6.30 0.05 5.00 13.20    
    29271 43834   Alpha Mensae G5 V 10 5.10 0.10 3.90 12.80    
    64924 115617 AB 61 Virginis G6 V 9 4.80 0.04 2.40 12.30    
    85667 158614 AB BD -00° 3300 (Ophiuchus) G8 IV-V 16 5.30 0.03 10.60 12.00 13.40  
    99240 190248   Delta Pavonis G7 IV-V 6 3.60 0.27 6.60 11.40 13.40 Star
    43726 76151   BD -04° 2490 (Hydra) G3 V 17 6.00 0.01 4.20 10.60 16.80  
    98921 190771 AB BD +38° 3896 (Cygnus) G5 IV 19 6.60 0.03 3.70 9.20 14.60  
    113357 217014   51 Pegasi   [planet found] G4 V 15 5.60 0.16 4.80 9.20 12.00 Star
    53721 95128   47 Ursae Majoris [planets] G0 V 14 5.10 0.01 5.30 8.70 11.90 Star
    79672 146233 AB 18 Scorpii G1 V 14 5.60 0.03 0.50 8.30 13.10  
    49081 86728 AB 20 Leonis Minoris G2 V 15 5.60 0.22 3.30 7.20 10.40  
    24813 34411 AB 15 Lambda Aurigae G2 IV-V 13 4.90 0.11 3.90 6.70 8.80  
    15457 20630 ABC 96 Kappa 1 Ceti G5 V 9 5.00 0.06   6.70 13.40  
    48113 84737   BD +46° 1551 (Ursa Major) G0.5 V 18 5.20 0.10 5.30 6.60 7.60  
    77257 141004   27 Lambda Serpentis G0 V 12 4.40 0.05 4.10 6.50 9.70  
    2021 2151   Beta Hydri G2 IV 7 2.90 0.01 4.90 5.40 5.90  
    64792 115383 AB 59 Virginis G0 V 18 5.20 0.05 3.30 5.10 8.40  
    32480 48682 AB 56 Psi 5 Aurigae G0 V 17 5.30 0.02 2.00 4.50 6.80  
    14632 19373 AB Iota Persei G0 V 11 4.20 0.16 3.50 4.40 5.90

    Stellar data courtesy of the Centre de Données astronomiques de Strasbourg.
    From "Geneva-Copenhagen Survey of Solar neighbourhood," Nordstrom B., et al, Astron. Astrophys. 419, 989 (2004)
    Alpha Centauri age from "F & G solar neighbourhood stars new ages," Ng Y., et al, Astron. Astrophys. 329, 943 (1998)

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    Composite Skymap of Ancient and Rich Star Locations Skymap Selector screen from "Stars in the NeighborHood" software.
    See "Software Review" for more information.
      Sky locations of
    selected ancient, rich stars

    Hover mouse over Sky Map to show HD star numbers

    The composite skymap (left) shows the locations of the ancient and rich stars listed in the table above.

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