How long before the expansion of the Universe causes our Earth to drift away from the Sun?

Is it possible for a planet, such as Mars, to develop a liveable atmosphere on its own? What would it take?

If the moons of Jupiter and Saturn become habitable when the Sun is a red giant, will we be able to get every human off the Earth through multiple trips (over centuries)? How will the last flight work?

Sadly billions of people would die and not be able to find a way off the planet should the sun become a red giant, even in the future.

Not to worry, though! All life on Earth will cease long before the sun becomes a red giant. As the sun ages it gets hotter and hotter. We estimate that in about a billion and a half years it will be so hot all the oceans, rivers and lakes will have dried up and all vegetation and everything else will cease to be. All that happens billions of years before the sun becomes a red giant.

On the upside, we will finally get rid of all the bad people. By that time, Earth might look something like this:

Has there ever been, or will there ever be, a time when the earth was/will be void of all evil, rogue, repressive (use your own adjective) regimes?

Will Earth ever be rid of bad guys? Yes, because in the future there will be no life on Earth at all.

When all else fails, the sun will grow so hot as it ages the oceans and fresh water will dry up. Vegetation and all other lifeforms will cease to exist. Then the sun will grow and become a red giant, completely swallowing Mercury and Venus, and possibly Earth, but if not Earth, Earth would be too close for comfort from the sun’s surface.

At that point I suspect Earth will be completely void of all evil, rogue and repressive regimes and bad guys. In fact, it will be completely void of pretty much everything and look much like what Venus looks like today!

Could space colonization become the main ideology of humanity?

When we completely destroy our planet’s environment then and only then space conization would become our “main ideology.”

Sadly, however, even space colonization leads to the same question – will we destroy the next planet just like this one?

Is, or will, our Sun also become a variable star? If so, what kind?

Not a variable star with fluctuating brightness, but our sun is getting brighter gradually over time. As the fuel in the sun is spent the sun gets 10% brighter and 10% hotter every billion years. So we estimate in a couple billion or so years the oceans will dry up and all life on Earth will cease. Earth will become much like Venus is now. Eventually the sun will turn into a red giant and expand to swallow Mercury, Venus and probably Earth.

When will a rogue planet collide with Earth?

Worry about the future of life itself on the only planet ever found to have life.

When will a rogue planet collide with Earth? Probably never again, although smaller objects like comets might hit us. However the future for Earth and life on Earth doesn’t look good either way.

For a planet to collide with another is like a bullet hitting a bullet. Space is big compared to a tiny planet, and the chance that a rogue planet might actually collide here is a long shot, even though we believe it may have already happened once.

It’s pretty unlikely to happen again because that was back in the day when the solar system was still forming and more volatile.

But what is happening is that the sun is running out of fuel. Every billion years or so it gets about 10% hotter as a result. We estimate that in 1.1 billion years it will be too hot to sustain life on Earth. The oceans will evaporate, greenhouse gasses will take over and Earth will become like Venus: too hot and raining sulfuric acid. All this happens way before the sun becomes a red giant and destroys Mercury, Venus and probably Earth.

So you don’t have to worry about that rogue planet hitting us. You have to worry about the future of life itself on the only planet ever found to have life.

Am I a pessimist or a realist?