Most realistic simulation of the Earth during the Suns red giant phase?
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21-08-2013, 01:56 PM
Most realistic simulation of the Earth during the Suns red giant phase?
We all know the theory that in a couple billions years the sun will enlarge and engulf mercury and venus, and maybe possibly earth.

But i'm sceptical since wouldn't the mass of the sun have been greatly reduced, and so the planets will drift further outward.. perhaps out of reach of the growing sun? Could the drift possibly keep the earth in a near habitable zone?
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21-08-2013, 03:13 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
(21-08-2013 01:56 PM)PoolBoyG Wrote:  We all know the theory that in a couple billions years the sun will enlarge and engulf mercury and venus, and maybe possibly earth.

But i'm sceptical since wouldn't the mass of the sun have been greatly reduced, and so the planets will drift further outward.. perhaps out of reach of the growing sun? Could the drift possibly keep the earth in a near habitable zone?

No, the mass of the sun won't be reduced until it's well into being a red giant. As the diameter increases, the outer layers will slowly dissipate as they experience less and less gravity due to distance.

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21-08-2013, 03:19 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
Stupid iron...always destroying everything.

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21-08-2013, 10:28 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
(21-08-2013 01:56 PM)PoolBoyG Wrote:  We all know the theory that in a couple billions years the sun will enlarge and engulf mercury and venus, and maybe possibly earth.

But i'm sceptical since wouldn't the mass of the sun have been greatly reduced, and so the planets will drift further outward.. perhaps out of reach of the growing sun? Could the drift possibly keep the earth in a near habitable zone?

No, the mass of the star is not reduced during this phase. The density of the star (mass per unit volume) would decrease dramatically, but mass is conserved.

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23-08-2013, 01:14 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
Most mass is conserved, Some small percentage will be lost through the radiation produced through the fusion occurring in the core. There is also solar wind, but I don't know how much of an effect it has on the mass of the sun. But surely neither of these will lower the mass of the sun enough to let the earth drift hundreds of millions of kilometers farther out, which I presume would be required for us to stay in the habitable zone (at least).

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24-08-2013, 11:25 AM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
Actually, I take that back. The sun's mass is always reducing as it is being converted into energy via nuclear fusion.

The total power output of the sun is 3.8 x 10^26 watts. (380,000,000,000,000,000,000,000,000 watts!!)

By the formula E=mc^2, that means that the sun's mass decreases by 4,200 kg every second.

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24-08-2013, 12:31 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
(21-08-2013 01:56 PM)PoolBoyG Wrote:  We all know the theory that in a couple billions years the sun will enlarge and engulf mercury and venus, and maybe possibly earth.

But i'm sceptical since wouldn't the mass of the sun have been greatly reduced, and so the planets will drift further outward.. perhaps out of reach of the growing sun? Could the drift possibly keep the earth in a near habitable zone?

Well.

(21-08-2013 03:13 PM)Chas Wrote:  No, the mass of the sun won't be reduced until it's well into being a red giant. As the diameter increases, the outer layers will slowly dissipate as they experience less and less gravity due to distance.

(21-08-2013 10:28 PM)Carlo_The_Bugsmasher_Driver Wrote:  No, the mass of the star is not reduced during this phase. The density of the star (mass per unit volume) would decrease dramatically, but mass is conserved.

(23-08-2013 01:14 PM)Adenosis Wrote:  Most mass is conserved, Some small percentage will be lost through the radiation produced through the fusion occurring in the core. There is also solar wind, but I don't know how much of an effect it has on the mass of the sun. But surely neither of these will lower the mass of the sun enough to let the earth drift hundreds of millions of kilometers farther out, which I presume would be required for us to stay in the habitable zone (at least).

Mass is indeed lost as the sun radiates. As a star's density decreases and its radius increases, that rate of loss increases (less escape energy is needed). By the late stages of a sun-like star's life this is actually pretty substantial. Offhand (ie, I am not looking up any of this, so it may well be totally wrong) it is likely that our sun will lose 25%-30% of its mass as it expands to its red giant phase.

Whether Earth is doomed or not depends on calculations that cannot be made with any certainty. The sun's tidal forces may well cause orbital deceleration, which would cause the Earth to fall inward and be consumed, but it is also possible for acceleration to result, in which case the Earth would indeed assume a higher orbit as the sun loses mass. If so it would eventually escape to interstellar space, as with most of the original solar system mass. The dramatic increase in solar intensity would ensure that Earth will be by then far from habitable regardless.

A star like our sun will eventually undergo successive waves of expansion and contraction as it forms layers and cycles up through fusing heavier and heavier elements. This pushes off much larger amounts of matter, leaving a white dwarf behind (condensed Fermionic electron gas). The white dwarf amounts to a rather small percentage of the original stellar mass, and barring stellar collision or some such it will last pretty much forever (or at least as long as any matter will).

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24-08-2013, 01:19 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
Not really what you asked for but I don't care. Tongue Dude makes cool animations.








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24-08-2013, 07:54 PM (This post was last modified: 24-08-2013 07:58 PM by Carlo_The_Bugsmasher_Driver.)
RE: Most realistic simulation of the Earth during the Suns red giant phase?
Quote:Mass is indeed lost as the sun radiates. As a star's density decreases and its radius increases, that rate of loss increases (less escape energy is needed). By the late stages of a sun-like star's life this is actually pretty substantial. Offhand (ie, I am not looking up any of this, so it may well be totally wrong) it is likely that our sun will lose 25%-30% of its mass as it expands to its red giant phase.

Actually the sun will only lose about 2 trillionths of its original mass over the course of it's ~9 billion year life and loses very little mass during the Red Giant phase itself. However at the end of that phase it will shed over 99% of its matter to form a planetary nebulae, with the fraction of a percent of matter that remains becoming a White Dwarf.

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24-08-2013, 08:48 PM
RE: Most realistic simulation of the Earth during the Suns red giant phase?
(24-08-2013 07:54 PM)Carlo_The_Bugsmasher_Driver Wrote:  Actually the sun will only lose about 2 trillionths of its original mass over the course of it's ~9 billion year life and loses very little mass during the Red Giant phase itself. However at the end of that phase it will shed over 99% of its matter to form a planetary nebulae, with the fraction of a percent of matter that remains becoming a White Dwarf.

We've all been really vague in terms of timescales, and I, at least, was sloppily shifting scope from our sun to main-sequence stars generally Tongue.

The thermal pulses of the giant phase coincide with expulsion of significant amounts of matter. In fact this is observable in many shrouded giants. This is in the life stages prior to the final expulsion of the planetary nebula; though of course the end result is much the same. The larger the star, the more significant this is, and ours is towards the shrimpier end of the spectrum, but it is a factor nonetheless.

Mass loss prior the giant phase is indeed negligible; but significant mass loss will occur as the sun's radius expands, and indeed will already have occurred by the time the sun's radius begins to reach Earth's (present) orbital radius. It is down to the tidal forces of the expanding stellar surface whether the Earth is pulled in or kicked out. It is indeed rather more likely to be the former than the latter.

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