[extropy-chat] Re: Animals

Alfio Puglisi puglisi at arcetri.astro.it
Fri Feb 13 11:29:16 UTC 2004

On Fri, 13 Feb 2004, Eugen Leitl wrote:

>On Fri, Feb 13, 2004 at 01:33:23AM +0000, Christian Weisgerber wrote:
>> Reference?
>> (I can't find anything on this.)
>Mid-Life Crisis for the Earth
>5.6 Gyr (1.1 Gyr from today):
>    * Sun 10% brighter: ~1.1 Lsun
>    * Cause a moist greenhouse effect on Earth, driving away most of the
>    * water in the air.

This increase is common for small main-sequence stars, like our Sun. The
reason is that hot fusion is really difficult. At the ~15 million degrees
and high pressure in the Sun's nucleus, the average proton must wait ~14
billions years before undergoing fusion. Since the Sun was born only 5
billions years ago, right now it's shining only thanks to the "lucky"
protons that are undergoing fusion much earlier.

Slowly, the probability that each proton undergoings fusion goes up, and
the amount of energy produced goes up as well. The Sun will stop fusing
hydrogen in another 5 billions years, before the maximum energy output is


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