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Dgennero
2004-Apr-17, 04:41 PM
I'm interested in the fate of the Sun as it grows old.
I've consulted several books on this, and there seems to be some uncertainty:

1.)
- The Sun will remain unchanged (with a slight gradual increase in energy output) for the next five billion years

versus

- The energy output will double within the next billion years making earth uninhabitable then

2.)
- The Sun, when becoming a red giant, will have a diameter about 50 times its current diameter

versus

- The diameter of the red-giant-Sun will engulf earth's orbit

3.)
- The Sun will remain a red giant for a billion years

versus

- The Sun will remain a red giant for only a few million years


What is right?
Also, I'd like to know if it has been determined, what spectral class the Sun will have as a red giant, and which absolute magnitude.

Avatar28
2004-Apr-17, 07:13 PM
As I understand it, though I'm hardly an expert:


I'm interested in the fate of the Sun as it grows old.
I've consulted several books on this, and there seems to be some uncertainty:

1.)
- The Sun will remain unchanged (with a slight gradual increase in energy output) for the next five billion years

2.)
- The diameter of the red-giant-Sun will engulf earth's orbit

3.)
- The Sun will remain a red giant for a billion years

Brady Yoon
2004-Apr-17, 07:36 PM
1.)
- The Sun will remain unchanged (with a slight gradual increase in energy output) for the next five billion years 2.)
- The Sun, when becoming a red giant, will have a diameter about 50 times its current diameter

For #3, I think it's somewhere between a billion and a few million years ago.

I'm not sure, but it would be similar to Arcturus, spectral class most likely in the K range, and an absolute magnitude of around 0.

sol_g2v
2004-Apr-17, 11:20 PM
The Once and Future Sun (http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html)

Brady Yoon
2004-Apr-18, 01:00 AM
:o That's the best link on stellar evolution I've ever seen. Thanks!! :D

Normandy6644
2004-Apr-18, 05:54 AM
The Once and Future Sun (http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html)


Wow great link. The diagrams are excellent.

yorkshire_guy
2004-Apr-18, 12:57 PM
The Once and Future Sun (http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html)

I agree thats a great link on stellar evolution. I'm interested to see that the Earth might survive the red giant phase, albeit as a parched cinder! It did make me think about one possibility. Assuming the luminousity of the Sun at the beginning of its white dwarf phase is 3500 times present-day solar luminousity and the Sun then fades slowly over trillions of years. At some point the Sun will be at a comfortable luminousity again to place the Earth within its habitable zone. If somehow the Earth has replenished its atmosphere and at least some of its water - perhaps through residual geological activity or by capturing material from the planetary nebula - then is it not possible that life on Earth could have a second flowering? I suspect this is not possible as by the time the Sun has cooled sufficiently, the Earth's interior might have completely solidified rendering the planet geologically inert. Also, the planetary nebula will probably have dispersed. Then again, presumably the Oort cloud will still exist and so the occasional cometary impact will dump some water and organic molecules onto the Earth's surface - but would this be enough? I've never seen any articles concerning life on planets orbiting white dwarfs, but it is an interesting thought that the Earth might have life after death!

Sticks
2004-Apr-18, 02:33 PM
How about building a huge rocket motor to push the Earth out, as the sun expands ?

How feesible is this?

I read some where of a proposed method of changing the Earth's orbit using an asteroid.

Any clues on that ?

Kullat Nunu
2004-Apr-18, 03:37 PM
How about building a huge rocket motor to push the Earth out, as the sun expands ?

How feesible is this?

Too late, and probably impossible. Earth will be completely dead probably in about 1-2 billion years when Sun becomes so hot it starts to boil oceans. All higher lifeforms like animals and plants may die out in only a half billion years. When Sun turns to red giant life has been gone for a long time. During red giant phase even planets and moons from Mars to Uranus will be too hot to sustain life.


I read some where of a proposed method of changing the Earth's orbit using an asteroid.

Any clues on that ?

More feasible. Neptune probably wandered to its current position when it flung asteroids from primordial Kuiper Belt. Only problem is, where to go?

Unless we destroy ourselves our technological status will eventually be high enough to develop spacecraft and leave this star system.

Brady Yoon
2004-Apr-18, 04:50 PM
When the sun gets to 3,000 solar luminosities, even Pluto will become a little hot...

This made me think a little. If the Earth was orbiting Rigel, at 40,000 solar luminosities, we would have to be at 200 A.U. or 5 times farther than Pluto.

And for Eta Carinae, it would be 2,000 A.U., 50 times farther than Pluto. :o

dakini
2004-Apr-18, 05:45 PM
i'm curious as to what happens to the planets when a star finalyl throws off its outer layers and all that. does the gas from the expanding planetary nebula break up the planets, or like push them back?

Brady Yoon
2004-Apr-18, 05:50 PM
The release of gases in a planetary nebula aren't much at all compared to a supernova explosion or even a nova. The planets itself wouldn't be affected much, but their orbital semi-major axes will increase because the sun loses so much mass.

sol_g2v
2004-Apr-18, 09:31 PM
I should point out that the link I posted earlier neglects to take into account the effect of solar tides, which would tend to draw the inner planets closer to the expanding sun. Also if the the sun retains most of its mass before it expands to maximum size, it will "catch up" to the planets before they can move away. So Venus will most likely not survive the red giant phase but the fate of Earth is really unknown. It's right at the razor's edge of being fried or frozen. That could be the situation for all planets that are in the HZ of their stars, which is really quite ironic.

dakini
2004-Apr-18, 09:41 PM
i was looking forward to the earth being vaporizd in a way. i mean, if they don't leave this planet, and the planet doesn't get burnt up in the sun and ejected with the planetary nebula material, then my molecules won't get reused... they'll just sit in the ground... well.. wherever they end up.

Brady Yoon
2004-Apr-18, 10:49 PM
i was looking forward to the earth being vaporizd in a way. i mean, if they don't leave this planet, and the planet doesn't get burnt up in the sun and ejected with the planetary nebula material, then my molecules won't get reused... they'll just sit in the ground... well.. wherever they end up.

That's a good way to put it. :D But I don't think we should be worried at all. I doubt our civilization will last any more than 1 million years, let alone a billion.

jaeger
2004-Apr-19, 12:01 AM
I read some where of a proposed method of changing the Earth's orbit using an asteroid.

Any clues on that ?

Larry Niven wrote an interesting SciFi novel in the late 70s called "A World Out of Time" where Earth has been moved out of its current orbit to an orbit around Jupiter because the sun has become a red giant. It's not part of Niven's "Known Space" tales, but a good read nonetheless. Can't find my copy and can't remember Niven's idea for moving Earth out of orbit.

AstroSmurf
2004-Apr-19, 09:22 AM
Larry Niven wrote an interesting SciFi novel in the late 70s called "A World Out of Time" where Earth has been moved out of its current orbit to an orbit around Jupiter because the sun has become a red giant. It's not part of Niven's "Known Space" tales, but a good read nonetheless. Can't find my copy and can't remember Niven's idea for moving Earth out of orbit.
Simple.
1) Build a giant fusion-powered "jet engine" in the upper atmosphere of, say, Uranus.
2) Steer Uranus close to Earth, close enough that Earth becomes a moon of Uranus.
3) Head on out to wherever you want to put Earth.

The only obstacle is making sure the planet is big enough that you won't run out of reaction mass. Say what you will about Niven, but he's not afraid of BIG thought experiments.

PhantomWolf
2004-Apr-19, 09:56 AM
Well by the time it happens we'll have figured out tractor beams, so just build a really big station, with a big one on ech side, about halfway between Earth and Saturn, then lock one beam onto Saturn and one onto Earth and drag the Earth out to a safe orbit.

eburacum45
2004-Apr-19, 10:59 AM
The release of gases in a planetary nebula aren't much at all compared to a supernova explosion or even a nova. The planets itself wouldn't be affected much, but their orbital semi-major axes will increase because the sun loses so much mass.

Stars in the planetary nebular phase will be throwing out a lot of dust, no?

I imagine that when we examine the remaining planets of a white dwarf star they will be covered in dust deposits, carbon or silicon or both, perhaps other elements too.

HenrikOlsen
2004-Apr-19, 11:46 AM
Well by the time it happens we'll have figured out tractor beams, so just build a really big station, with a big one on ech side, about halfway between Earth and Saturn, then lock one beam onto Saturn and one onto Earth and drag the Earth out to a safe orbit.

Remember that Niven's solution doesn't require new theory, just slightly bigger engineering than we're used to.

The tractor beam solution requires new theory, and there's no way to predict if a new theory will exist.

It's the different between science fiction and sci-fi

On the other hand, by the time it's relevant we won't be recognisably human anyway, so why worry? :)

Dgennero
2004-Apr-19, 02:27 PM
@sol_g2v: Hypermegacool, answers all my questions.
As for the planetary nebula - I think without a companion star or a shock wave due to a supernova nearby, there will be none for the Sun.

ZaphodBeeblebrox
2004-Apr-19, 03:37 PM
The best idea I've heard for a way to move the Earth, is to put an Anti-Matter Rocket on the Far-Side of the Moon.

That keeps the radiation from striking the Eath, and even more importantly, both bodies will be moved by the thrust, if its vector is correct.

Further, we wouldn't even need to stay in System.

Just light up the Near-Side of the Moon with Bright Lights to simulate the Sun, Bon Voyage!