Re: Semi-OT Earth's five space dooms!



robert casey wrote:
The five dooms are:
1.) Sun blows up. In about 5 billion years or so it gets very big
2.) Sun burns out. In about 7 billion years to white dwarf stage
3.) Rogue star hits Sun. Very long odds on that.
4.) Giant comet hits Earth ("science thinks it unlikely" although of all the scenarios presented, this one seems the most likely in the short run).

That one is the most likely, though the historical record suggests that this doesn't happen all that often. One like that one that hit in Russia a hundred years ago could do significant damage to a small city.
5.) Moon descends, pummels Earth with giant meteorites. Maybe in a few billion years, 1999 notwithstanding.


All the ones except the comet impact have fairly broad estimates at to when they will occur.
Sun goes red giant, melts Earth - 5 billion years from now.
Sun conks out, becomes white dwarf - 6 billion years from now.
Rogue star hits Sun - possibly 4 billion years from now, when Milky Way galaxy collides with Andromeda galaxy.
Moon breaks up, forms ring of decaying debris that eventually all falls on Earth - depends on what happens when Sun goes red giant. If solar atmosphere engulfs Earth-Moon system for a long period of time, they may both either boil away or fall into Sun.
If for a shorter period of time, then Moon may may lose enough velocity that it breaks up into a ring at around 11 thousand miles up (think of the tides!).
If red giant phase is very short before collapse into a white dwarf, then Earth and Moon continue to orbit each other as a tidally locked pair with around a 47 day period, and have a very long lifetime, due to lack of solar wind from white dwarf Sun.
I think we can be fairly certain that there will be a comet or asteroid impact on Earth large enough to wipe out the current biosphere long before any of the above occur.
What makes this interesting is even if some huge impact killed all life on Earth tomorrow, it would still have time to re-evolve to the current state before the Sun went red giant.
If even things as complex as worms and some plants survived the impact, then they would be able to evolve up to the present level of complexity in around 1/2 billion years, which means you could have 10 separate complete evolutions of higher life before the Sun ends the game once and for all.

Pat
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