When the sun eventually expires and swells to engulf Earth, might the remnants of landfill and deeply buried nuclear waste be recycled to听form the star dust that will become听new planets or life forms?
Ron Dippold
San Diego, California, US
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Quite possibly! Though you certainly won鈥檛 be able to say, 鈥淥h听hey, that was my old shirt鈥�.
In the first stage, after the sun runs out of hydrogen in its core in听about 5 billion years, it will initially collapse a bit from loss of听outward pressure 鈥� but all of that听gravitational energy from in-falling mass will be a huge energy injection. It will start burning some of the outer hydrogen in a听shell around the core, and begin expanding into a red giant. It will听get over 1000 times brighter. The听intense radiation will blast Earth鈥檚听atmosphere into outer space. Earth鈥檚 surface temperature will reach over 1500掳C. At that temperature, its crust and most other things will just melt into a听sea of magma. A few things may听survive intact 鈥� metals like听tungsten and molybdenum can听survive over 2500掳C.
When the sun expands, Earth鈥檚 surface temperature will reach over 1500掳C and most things will melt into a sea of magma
Some听synthetic materials, like aluminium oxide and zirconia, are听similarly hardy, and many gems, like diamonds, sapphires and rubies, would be fine.
Earth will drift outwards a bit because the sun is losing mass, but听in the second stage 鈥� about 7.5听billion years from now, according to most theories 鈥� the听sun will still swallow Earth.
The entire planet will disintegrate before too long from听the heat, the buffeting by dense plasma, and the tidal forces. At this point, everything will become ionised plasma like the听rest of the sun 鈥� even those things that avoided melting in听the听first stage.
The sun is about eight times too听small for a core-collapse supernova. However, it still has several coughing fits to go through as it runs out of various elements and starts fusing heavier ones. Eventually, it will blow off its outer听layers in an expanding cloud听of gas and radiation called a听planetary nebula. The remaining sun will shrink to a white dwarf, which, in theory, can glow for trillions of years 鈥� if the universe lasts that long. Anything stuck in that is never getting out, unless a听black hole rips it to pieces. But most of Earth would still be in those outer layers blown off as a听planetary nebula. As that cools听over millennia, the atoms in听the nebula will arrange into tiny听grains of cosmic dust and interstellar gas. In billions of years, these may become part of a large molecular cloud like the one that became our solar system, and might one day collapse again into a brand new solar system. My Iron Maiden concert shirt will live on!
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Hillary Shaw
Newport, Shropshire, UK
The first question here is will the听sun engulf Earth as it becomes a 听red giant? Probably it will, despite the reduction in the sun鈥檚 mass 鈥� resulting in Earth orbiting further out 鈥� as the sun鈥檚 extended atmosphere may cause drag on听Earth, slowing its orbit and causing it to fall back further in.
Consuming the remains of Earth, Venus and Mercury, the red-giant sun expands, throwing off material like dust and gas that may well end up as part of another solar system, possibly hosting life. That life probably won鈥檛 use our nuclear-waste atoms 鈥� which by then will have decayed to stable isotopes anyway 鈥� directly, but if it听is intelligent, it may find uses for these heavy elements as we have.
However, if the red-giant sun听doesn鈥檛 consume Earth, its alternative is far more dismal, dark and lonely. The red giant loses fuel and transitions into a white dwarf. The husk of Earth orbits the white-dwarf sun for quadrillions of years听as it cools to a black dwarf. A听passing star may strip Earth away, or it may fall into another star, or a听neutron star, or a black hole. At some point, this entity may collide with another black hole or neutron star, and some matter containing heavy atoms听is听ejected, possibly to听seed听another听life-bearing planet.
Or this collision never happens, and Earth and the black-dwarf sun linger on, and in 1020 years, Earth鈥檚 orbit decays so it falls into the black-dwarf sun. Or Earth survives, perhaps ejected and wandering space, and in 1033 years, proton decay may convert it to radiation.
Or proton decay does not occur,and in 10100 years, the last black hole has evaporated and the universe is now a thinning, cooling void of sparse radio-wave radiation and matter. Time becomes meaningless and a dark infinity of nothingness 鈥揷ontaining odd lumps of matter, like Earth, that never fell into the now-extinct black holes 鈥� lingers on forever. Very occasionally, and ever less frequently, distant faint flashes of light occur as objects like black dwarfs and stray planets collide. Extremely unlikely, but possibly, a single, small, dim, red main-sequence star forms, with a life-bearing planet. It is doomed to a solitary, albeit long,听existence in the black, empty void. Then nothing. Forever.
听
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