S46@DHDURZ1.BITNET (GUNNAR RADONS) (06/19/91)
To Michael Rivero and all who are interested;
I am sorry that I had not the time to grab the part of your reply to the
Extraterrestial intelligence discussion, since I just received in and I'm in
a hurry. But I have to reply to your saddly very wrong reply on metallicity.
1) Low metallicity means lower metallicity than the sun. The default value
for the solar metallicity (anything beyond Helium4) is 0.02. That means
only two percent of the sun exsist of elements heavier than H, and He and
their isotopes.
2) Sun and the solar planets are born from the same molcule cloud, which itself
seemed to have been enriched by a supernova. This relates back to element
abundance measurements from meteorites.
3) Now one topic where I am very shure about (the other two were guesses from
the literature and my memory).
We see many more population I stars around us then population II stars.
This is due to the fact, that it is very difficult to determine whther an
M-dwarf is from poulation I (and therefore young) or from population II
(old). Futher, most tstas we see in the solar vicinity are K and 1-Dwarfs.
You may wnat to check the Gliese-Catalogue of nearby stars for proof.
4) The space density of stars along the z- axis (perpendicular to the galactic
plane) is more or less gaussian (even if you beleave in the isothermal models
of Cam, Schwarzschild etc., the conclusions won't change).
This distribution is the same for young and old stars, since it is governed
by the global potential of the galactic disk. The stars make oszillations
perpendicular to the galactic disk. Therefore they are constantly
accelerated when they run toward the disk, they swing across, and get
decelerated again. But this time it swings further out, since the mass in
the galactic disk had changed. The idea is that the gas from the galactic
halo permantently rains into the galaxy (I think this is even observed)
and slowly raises the mass inside the galactic disk, deepening the potential
well.
Therefore: Even stars with metallicity less than 0.00001 have lots of
heavy metals (in kilograms), but their relative amount is small. Whether
there is a planet allowing live depends on how old the star is, how the
accretiaon of dust and grains to protoplanets works, how much mass the
planet has, how and whether their will be hight emeperature core,
water, or other solvents.....
I am sorry that this got that long...
Gunnar Radons, s46@dhdurz1.bitnet