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Comment by kubafu | Hacker News Reader

And another factor will be the Sun growing in size due to hydrogen exhaustion: https://en.wikipedia.org/wiki/Sun#After_core_hydrogen_exhaus...

But at the time also the Earth's average distance from the Sun will grow, wouldn't it?

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No, it won't. Earth will either be a scorched planet or will be engulfed by the Sun. And it won't take those 5 billion years either for life to vanish from Earth. We're currently near the inner edge of Goldilocks zone (Mars is just a bit outside of the outer edge) and we have only like 500 million years. Either start colonizing other planets or we die, there nothing in between (assuming we don't destroy ourselves meanwhile).

Third option, we can take advantage of repeated gravitational slingshots to transfer orbital kinetic energy from Jupiter to Earth via an asteroid going repeatedly between both planets, gradually increasing Earth's orbit.

(I'm not an astrophysicist, I just read about this idea a few years back and it stuck in my mind).

I guess Jupiter would be more efficient but it would be really neat to do this to mars bringing it nearer to the habitable zone/earth

The limit on earth's habitability is determined by permanent sequestration of atmospheric CO₂ through the carbonate-silicate cycle, not insolation. Once CO₂ drops below a certain level, photosynthesis will no longer be possible and all remaining ecosystems will collapse.

(Don't mistake that as an endorsement of burning fossil fuels — climate change is operating at a rate measured in decades, CO₂ drawdown via the carbonate-silicate cycle operates at a rate measured in hundreds of millions of years)

True, I had forgotten that. But I assume we can fix that over this kind of timescale.

While I am not generally a proponent of waiting until the last minute to worry about a problem, I think with a time frame of hundreds of millions of years, we can afford to procrastinate a bit.

Given how far we've come in the past 150 years, no sense in waiting for an existential threat. Let's get crackin'!

While sun would grow in size, it would also be losing mass. This reduces the centripetal force of revolution. The orbit would indeed expand.

The loss of mass is insignificant and we are talking 0,5B years.

Sun will be loosing a lot of mass later, but that will be way after Earth has been baked to a crisp.

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