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Tom Mazanec
2004-Jun-12, 06:40 PM
What is the oldest possible biosphere for a planet? I imagine it might be a combination of a late G star (for a long main sequence lifespan) combined with a two or three Earth mass planet (to hold down tidal slowing of rotation, prolong plate tectonics, and keep an atmosphere longer (although the last is probably irrelevant)) would be best. What would the span be, about ten or twenty eons or so?

Brady Yoon
2004-Jun-12, 06:46 PM
It would be an M spectral type main sequence star. These stars are so dim that they can last well over a trillion years. The downside is that the habitable zone for these stars is extremely small, and the life that develops there may not be life as we know it. Tidal locking would occur very quickly because the planet would have to be much closer to the star to get the same light. And life that forms will be sensitive to red light, perhaps developing infrared vision.

I think a G star is the best when it comes to life as we know it. There is a good balance between time for life to form and the size of the habitable zone. However, this is only assuming that life cannot form in other conditions.

Kaptain K
2004-Jun-12, 09:07 PM
A late "G" or early "K" type star would have a longer lifespan than the age of the universe (and a wider habitable zone than "M" type stars). So, after a few generations of LBV's (Luminous Blue Variables) had seeded the medium with heavier elements (circa 1 billion years), such a star could have formed with habitable planets that are still around and viable. So, figure on about 13 billion years or so!

Cougar
2004-Jun-13, 12:06 AM
So, figure on about 13 billion years or so!
That would be my guess.