crazyfingers
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- May 17, 2002
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There is an interesting recent story in Sky and Telescope (or perhaps it was Astronomy Magazine - I get both) about what is described as the habitable zone of the galaxy.
The issue has to do with the relative concentrations of available heavy elements which constitute the bulk of what sold planets like earth are made from.
These concentrations of available (as in not locked up in a star) heavy elements are not uniformly dispersed in the galaxy as some areas of the galaxy have higher concentrations of older stars.
Regions with mostly old stars have not had as many star generations to go nova and to therefore disperse heavy elements.
I might not be recalling exactly right but I think that the innermost regions of the galaxy has the highest concentration of heavy elements because there has been the largest number of star generations to go nova.
Our solar system is out along the spiral arm in what is called the thick ring (the center of the arm if you took a cross section of a spiral arm) where there are medium concentrations of heavy elements because there have been several star generations to populate the space with heavier elements.
The thin ring has fewer heavy elements because there are fewer stars to create heavy elements. Finally, globular clusters have low concentrations of available heavy elements because globular clusters tend to be made up of very old stars.
Anyway, it is out along the center of the spiral arms where our solar system is where there is the "best" concentration of heavy elements for earth like planets to form. Too high a concentration and you get very large solid planets which would have a difficult time maintianing land bass - water, being lighter than solid ground would cover the surface.
OTOH, with too low a concentration of heavy elements, you get lower mass solid planets which would have a hard time maintaining an atmosphere.
An interesting read anyway.
The issue has to do with the relative concentrations of available heavy elements which constitute the bulk of what sold planets like earth are made from.
These concentrations of available (as in not locked up in a star) heavy elements are not uniformly dispersed in the galaxy as some areas of the galaxy have higher concentrations of older stars.
Regions with mostly old stars have not had as many star generations to go nova and to therefore disperse heavy elements.
I might not be recalling exactly right but I think that the innermost regions of the galaxy has the highest concentration of heavy elements because there has been the largest number of star generations to go nova.
Our solar system is out along the spiral arm in what is called the thick ring (the center of the arm if you took a cross section of a spiral arm) where there are medium concentrations of heavy elements because there have been several star generations to populate the space with heavier elements.
The thin ring has fewer heavy elements because there are fewer stars to create heavy elements. Finally, globular clusters have low concentrations of available heavy elements because globular clusters tend to be made up of very old stars.
Anyway, it is out along the center of the spiral arms where our solar system is where there is the "best" concentration of heavy elements for earth like planets to form. Too high a concentration and you get very large solid planets which would have a difficult time maintianing land bass - water, being lighter than solid ground would cover the surface.
OTOH, with too low a concentration of heavy elements, you get lower mass solid planets which would have a hard time maintaining an atmosphere.
An interesting read anyway.
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