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Shrinking Sun


igosaur
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As the Sun is loosing something like 400 million tonnes a second in mass it must therefore be getting smaller. As it gets smaller its gravitational influence on the planets must therefore be lessening.

 

Is it therefore reasonable to say that as the Sun gets smaller the planets are very slowly drifting further and further away?

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well, it is getting less massive. but that doesn't necessarily mean smaller. infact, before it turns into a white dwarf it will get very much larger, so much so it could engulf the earth perhaps even mars.

 

although, the part about the planets slowly drifting is correct. although it would take longer than the life of the sun before it would let go of even the furthest kuiper belt objects.

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As the Sun is loosing something like 400 million tonnes a second in mass it must therefore be getting smaller. As it gets smaller its gravitational influence on the planets must therefore be lessening.

The Sun is losing 4 million metric tonnes per second due to fusion, not 400 million. You are off by a factor of 100. 4 million tonnes per second sounds like a lot of mass loss. It isn't when compared to the mass of the Sun itself. The solar mass is about 2×1027 metric tonnes. At the current rate, it will take the Sun another 15 billion years to lose a mere 1/1000th of its mass. The Sun will turn into a red giant and then a a white dwarf long before then.

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I stand corrected..

 

How about when the Sun has finally blown itself to bits and ends up as a white dwarf. How will that effect bodies like Pluto?

 

If the Sun 'itself to bits' it won't become a white dwarf...

http://en.wikipedia.org/wiki/Stellar_evolution#White_dwarfs

 

If the sun 'blows up' I'm guessing that every body in our Solar System would suffer greatly, including Pluto.

If it shrinks into a White Dwarf, then I'm not entirely sure, but I'm guessing that its gravitational influence would be significantly weakened, and perhaps Pluto would sort...float away...this is all guessing, by the way, I really have don't know. I'm hoping someone who knows more about the subject than I do will come along and give you a correct answer.

(cue Martin)

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The Sun is losing 4 million metric tonnes per second due to fusion, not 400 million. You are off by a factor of 100...

 

I'm impressed and I suspect you are right, but I want to check it against what I remember.

I remember that the total wattage output is around 3.6 or 4 times 1026 watts. (could be wrong, haven't looked it up lately)

 

so that would be how many joules per second and one changes joules to kilograms by dividing by 10^17

so that would be around 4 times 109 kilograms. which is 4 times 106 metric tonnes. Good! So we agree.

 

===============

 

I wonder. Is there an online handbook table of astrophysical quantities that we could all share.

I have an old print copy of Allen's astrophysics handbook which has all kinds of facts like this, with references to sources and so on. But AFAIK it is not online. where do you get your handbook-type info?

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