Effect on planet orbits around dying stars?

[wautd]

Take our own sun for exemple. Eventually, it'll run out of hydrogen and becomes a red dwarf. Will this change of density (and gravity) alter the distance of which the planets orbit? And how?

[Surlethe]

Take our own sun for exemple. Eventually, it'll run out of hydrogen and becomes a red dwarf. Will this change of density (and gravity) alter the distance of which the planets orbit? And how?

If you're living outside of a given body, its mass can be treated as a single point; therefore, so long as the Earth is orbiting outside of the surface of the Sun, the Earth's orbit will remain the same. The problem comes when the Sun expands out to Mars' orbit in its red giant stage; I'm not sure if the Earth will either vaporize, or move its orbit out.

Of course, long before the Sun subsumes the Earth, all life on the planet will have been scorched; the surface will be sterile and dry.

[GrandMasterTerwynn]

Take our own sun for exemple. Eventually, it'll run out of hydrogen and becomes a red dwarf. Will this change of density (and gravity) alter the distance of which the planets orbit? And how?

It will eventually run out of hydrogen and become a red giant swallowing Mercury, Venus, and likely Earth as well. Then it will become a white dwarf, after expunging its outer layers into a beautiful planetary nebula. As it loses mass, the surviving planets will spiral out into more distant orbits, since solar gravity will be decreasing, which means the planets will, effectively, get an energy boost, kicking them into higher orbits.

[wautd]

Take our own sun for exemple. Eventually, it'll run out of hydrogen and becomes a red dwarf. Will this change of density (and gravity) alter the distance of which the planets orbit? And how?

It will eventually run out of hydrogen and become a red giant

offcourse , typo in the OP (I havn't slept)

[Ariphaos]

In normal cases (IE, anything not going to go supernova), the star sheds more of its mass as it heats up faster and faster. This and the stellar wind slowly pushes the orbit of the star's planets outward, though mostly the mass loss - the Sun is expected to lose about half its mass, so the inner planets will recede quite a ways - possibly even to safety for Venus and almost certainly so for Earth.

Of course, Earth will be a dead, scorched world long before then.

[Sriad]

Take our own sun for exemple. Eventually, it'll run out of hydrogen and becomes a red dwarf. Will this change of density (and gravity) alter the distance of which the planets orbit? And how?

It will eventually run out of hydrogen and become a red giant

offcourse , typo in the OP (I havn't slept)

Well it'll be a white dwarf after the red giant phase...

A planet engulfed by a star in it's giant phase will tend to spiral inward as the gas it passes through robs it of momentum.

[Sikon]

If this is intellectual interest in what will happen to the solar system or other inhabited places, rather than a general astronomy question, the answer could be different. Changing the orbit of a planet like earth over a long period of time is surprisingly easy (relatively). For example, an asteroid as little as tens of miles in diameter could be enough to eventually move earth through an enormous number of repeated fly-by gravitational tugs over millenia (example). Of course, there are other possibilities like the planet being disassembled before then, but the "natural" future of earth being incinerated by an expanding sun is less likely.

[Jaepheth]

Take our own sun for exemple. Eventually, it'll run out of hydrogen and becomes a red dwarf. Will this change of density (and gravity) alter the distance of which the planets orbit? And how?

It will eventually run out of hydrogen and become a red giant

offcourse , typo in the OP (I havn't slept)

Though it would be infinitely cooler if our sun were to become a mining ship.

[CJvR]

The problem comes when the Sun expands out to Mars' orbit in its red giant stage; I'm not sure if the Earth will either vaporize, or move its orbit out.

The expansion of thin solar gasses to Earth orbit will generate drag that will slow the planet down sending it ever deeper into the the sun and eventually into the solar core,

[GrandMasterTerwynn]

The problem comes when the Sun expands out to Mars' orbit in its red giant stage; I'm not sure if the Earth will either vaporize, or move its orbit out.

The expansion of thin solar gasses to Earth orbit will generate drag that will slow the planet down sending it ever deeper into the the sun and eventually into the solar core,

That's one possibiliity. It all hinges on how far the sun expands, (which it will certainly expand past the orbits of Mercury and Venus, but it's unknown whether or not it will expand past Earth's orbit or not,) and how quickly it loses its mass and how much time it spends in the red giant phase of its life. If it expands too far, and stays that way for a long enough period of time, then Earth is screwed. It it doesn't get large enough to swallow Earth, then Earth's orbit will eventually widen as the Sun expunges mass into its planetary nebula.

[Ariphaos]

That's one possibiliity. It all hinges on how far the sun expands, (which it will certainly expand past the orbits of Mercury and Venus, but it's unknown whether or not it will expand past Earth's orbit or not,) and how quickly it loses its mass and how much time it spends in the red giant phase of its life. If it expands too far, and stays that way for a long enough period of time, then Earth is screwed. It it doesn't get large enough to swallow Earth, then Earth's orbit will eventually widen as the Sun expunges mass into its planetary nebula.

Well the mass loss from current solar winds are something like 10 million metric tonnes per year - trivial.

However, as a star swells into its red giant phase, the 'red' (it would look like a brilliant orange) portion of the star is actually just an extremely tenuous, hot gas flowing 'off' of it - a solar wind. Right now the particle density of the Sun's upper photosphere is about 1% of Earth's atmosphere. Swelling to Earth's orbit, I find the concept of the drag pulling Earth in faster than the mass loss lets it go to be a very suspect argument.