Question: How long will the solar system last?

Katie McDonald answered on 28 Jun 2012:

I was a bit stuck on this one, so I asked a physicist friend of mine. Here’s his answer:

“Hm, that’s a difficult one to answer properly. The sun’s about half-way through the main part of its life – it’s about 4.5 billion years old, and it should last another 5 billion years looking much as it does now. It will slowly get brighter through that period, which means that earth will be fairly uninhabitable about a billion years from now – the temperature will be too hot for liquid water to exist on the surface. (This also means that Mars will be a bit warmer though).

After that 5 billion years, the sun will expand out into a red giant, which means that it’ll grow to the point where its outermost edge is actually a little past where earth orbits just now. All the inner planets will be swallowed; however, it’s likely earth’s orbit will have grown a little by then, and the planet might just hang on at the edge. The outer planets will probably survive this though – they’re far enough away that they ought to be OK.

The red giant will only last about another billion years, of course, and once that’s died away, we’ll be left with a tiny white dwarf star, and a large ball of dust and gas. That ball of dust and gas will expand out and go on to seed other solar systems with the elements the sun created over its lifetime.

Finally, the white dwarf will slowly fade over another 5 billion years or so, eventually just leaving a tiny “black dwarf” – a cold remnant of the star. The interesting bit is that none of these exist yet though! The universe isn’t old enough to have let any star reach this age yet. The universe as a whole is only about 14 billion years old, and that’s not old enough yet for even the first stars to have gotten there, so we don’t know what happens beyond that point.”

Quite exciting, astrophysics. There’s still a lot of theorising without being able to ever test the theories!