Starship Asterisk*

BDanielMayfield wrote:What happens to planets and the elements they are made of when they are engulfed by stars becoming Red Giants?

"Five billion years from now, the Sun will have grown into a red giant star, more than a hundred times larger than its current size," ...

This metamorphosis will have a dramatic impact on the planets of our Solar System. Mercury and Venus, for instance, will be engulfed in the giant star and destroyed.

"But the fate of the Earth is still uncertain," continues Decin. "We already know that our Sun will be bigger and brighter, so that it will probably destroy any form of life on our planet. But will the Earth's rocky core survive the red giant phase and continue orbiting the white dwarf?"

BDanielMayfield wrote:What happens to planets and the elements they are made of when they are engulfed by stars becoming Red Giants?

Chris Peterson wrote:

BDanielMayfield wrote:
What happens to planets and the elements they are made of when they are engulfed by stars becoming Red Giants?

I think it's unclear. Terrestrial planets might survive for a time orbiting inside a red giant. But the drag may cause such planets to end up deeper inside the star, where they would not survive intact. In that case their elements would mix with the star and be partly dispersed by a supernova. If we stayed outside the red giant, our planet might survive the supernova largely intact, and continue in orbit around the remnant. But the supernova energy might vaporize at least some of the planet, again dispersing that material. It's even possible that the planet could be ejected from the system substantially intact.

• The Earth will probably have to contend with a helium flash first ... but a supernova

https://en.wikipedia.org/wiki/Red_giant wrote:
<<For the Sun and stars of less than about 2 M_☉ the core will become dense enough that electron degeneracy pressure will prevent it from collapsing further. Once the core is degenerate, it will continue to heat until it reaches a temperature of roughly 10⁸ K, hot enough to begin fusing helium to carbon via the triple-alpha process. Once the degenerate core reaches this temperature, the entire core will begin helium fusion nearly simultaneously in a so-called helium flash. In more-massive stars, the collapsing core will reach 10⁸ K before it is dense enough to be degenerate, so helium fusion will begin much more smoothly, and produce no helium flash.

An analogous process occurs when the central helium is exhausted and the star collapses once again, causing helium in a shell to begin fusing. At the same time hydrogen may begin fusion in a shell just outside the burning helium shell. This puts the star onto the asymptotic giant branch, a second red-giant phase. The helium fusion results in the build up of a carbon–oxygen core. A star below about 8 M_☉ will never start fusion in its degenerate carbon–oxygen core. Instead, at the end of the asymptotic-giant-branch phase the star will eject its outer layers, forming a planetary nebula with the core of the star exposed, ultimately becoming a white dwarf. The ejection of the outer mass and the creation of a planetary nebula finally ends the red-giant phase of the star's evolution. The red-giant phase typically lasts only around a billion years in total for a solar mass star, almost all of which is spent on the red-giant branch. The horizontal-branch and asymptotic-giant-branch phases proceed tens of times faster.

If the star has about 0.2 to 0.5 M_☉, it is massive enough to become a red giant but does not have enough mass to initiate the fusion of helium. These "intermediate" stars cool somewhat and increase their luminosity but never achieve the tip of the red-giant branch and helium core flash. When the ascent of the red-giant branch ends they puff off their outer layers much like a post-asymptotic-giant-branch star and then become a white dwarf.
.........................................................................
Prospects for habitability

Although traditionally it has been suggested the evolution of a star into a red giant will render its planetary system, if present, uninhabitable, some research suggests that, during the evolution of a 1 M_☉ star along the red-giant branch, it could harbor a habitable zone for several times 10⁹ years at 2 AU out to around 10⁸ years at 9 AU out, giving perhaps enough time for life to develop on a suitable world. After the red-giant stage, there would for such a star be a habitable zone between 7 and 22 AU for an additional 10⁹ years. Later studies have refined this scenario, showing how for a 1 M_☉ star the habitable zone lasts from 10⁸ years for a planet with an orbit similar to that of Mars one to 2.1×10⁸ yr for one that orbits at Saturn's distance to the Sun, the maximum time (3.7×10⁸ yr) corresponding for planets orbiting at the distance of Jupiter.

As of June 2014, 50 giant planets have been discovered around giant stars. However, these giant planets are more massive than the giant planets found around solar-type stars. This could be because giant stars are more massive than the Sun and more massive stars are expected to have more massive planets. However, the masses of the planets that have been found around giant stars do not correlate with the masses of the stars; therefore, the planets could be growing in mass during the stars' red giant phase. The growth in planet mass could be partly due to accretion from stellar wind, although a much larger effect would be Roche lobe overflow causing mass-transfer from the star to the planet when the giant expands out to the orbital distance of the planet.>>

neufer wrote:

Chris Peterson wrote:

BDanielMayfield wrote:
What happens to planets and the elements they are made of when they are engulfed by stars becoming Red Giants?

I think it's unclear. Terrestrial planets might survive for a time orbiting inside a red giant. But the drag may cause such planets to end up deeper inside the star, where they would not survive intact. In that case their elements would mix with the star and be partly dispersed by a supernova. If we stayed outside the red giant, our planet might survive the supernova largely intact, and continue in orbit around the remnant. But the supernova energy might vaporize at least some of the planet, again dispersing that material. It's even possible that the planet could be ejected from the system substantially intact.

• The Earth will probably have to contend with a helium flash first ... but a supernova :?:

Ann wrote:If the red giant Sun was to engulf the Earth and pull it deep inside itself and start digesting it, would that have any effects on the Sun itself?

Ann wrote:
If the red giant Sun was to engulf the Earth and pull it deep inside itself and start digesting it,
would that have any effects on the Sun itself?

BDanielMayfield wrote:Thanks for those responses Chris and Art. This question relates to my interest in the total number of planets, which would be a function over time that would need to include both planetary formation and destruction rates.

Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

BDanielMayfield wrote:
Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

rstevenson wrote:

BDanielMayfield wrote:What happens to planets and the elements they are made of when they are engulfed by stars becoming Red Giants?

I found an article at Science Daily that talks about the far future of our Solar System. It gives some sense of what happens -- which, of course, depends on how close the planet is to its star...

"Five billion years from now, the Sun will have grown into a red giant star, more than a hundred times larger than its current size," ...

This metamorphosis will have a dramatic impact on the planets of our Solar System. Mercury and Venus, for instance, will be engulfed in the giant star and destroyed.

"But the fate of the Earth is still uncertain," continues Decin. "We already know that our Sun will be bigger and brighter, so that it will probably destroy any form of life on our planet. But will the Earth's rocky core survive the red giant phase and continue orbiting the white dwarf?"

Rob

BDanielMayfield wrote:Thanks Rob. Nice article. I'm very confident (for reasons I can't get into here) that the Earth will survive the Sun's Red Giant phase. Some of that confidence is solidly scientific: (1) The Earth's orbit will naturally enlarge as the Sun looses mass over time. (2) Even us puny humans have already figured out how to exchange momentum between planets. A body could be placed in a solar orbit between the Earth and Jupiter such that some of the giant planet's momentum is slowly transferred to the Earth, lifting it into higher orbits!

Chris Peterson wrote:

Ann wrote:If the red giant Sun was to engulf the Earth and pull it deep inside itself and start digesting it, would that have any effects on the Sun itself?

In the most technical sense, yes. A grain of dust falling into the Sun affects it. But in the way I assume you mean, no. The metallicity of the Sun is at least 2%. So the dissolution of the Earth inside the Sun would increase the heavy element load by less than 0.02%. I don't see that having any significant effect.

Ann wrote:
I was wondering if the digestion of the Earth might give the Sun the hiccups.

https://en.wikipedia.org/wiki/Geophagia wrote:
<<Geophagia (also known as geophagy) is the practice of eating earth. It occurs in non-human animals where it may be a normal or abnormal behaviour, and also in humans, most often in rural or preindustrial societies among children and pregnant women.

Clay minerals have been reported to have beneficial microbiological effects, such as protecting the stomach against toxins, parasites and pathogens. Humans are not able to synthesize vitamin B12 (cobalamin), so geophagia may be a behavioral adaption to obtain it from bacteria in the soil. Mineral content in soils may vary per region, but many contain high levels of calcium, copper, magnesium, iron and zinc that are critical for pregnant women and peasants, as nature typically tends to favor behaviors based on survival.

There are obvious health risks in the consumption of soil that is contaminated by animal or human feces; in particular, helminth eggs, such as Ascaris, which can stay viable in the soil for years, can lead to helminth infections. Tetanus poses a further risk. Lead poisoning is also associated with soil ingestion.>>

Chris Peterson wrote:

BDanielMayfield wrote:Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

I think it is likely that the planet formation rate greatly exceeds the planet destruction rate, and will remain so until the planet formation rate reaches zero (at which point planets will occasionally be destroyed, but that will be a very rare thing). There is good reason to think that our Sun has already created hundreds of planets, the majority of which are no longer part of our system and which are unlikely to ever be destroyed.

BDanielMayfield wrote:

Chris Peterson wrote:

BDanielMayfield wrote:Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

I think it is likely that the planet formation rate greatly exceeds the planet destruction rate, and will remain so until the planet formation rate reaches zero (at which point planets will occasionally be destroyed, but that will be a very rare thing). There is good reason to think that our Sun has already created hundreds of planets, the majority of which are no longer part of our system and which are unlikely to ever be destroyed.

I think you are underestimating the planet destruction rate. Consider that the great majority of exoplanets found to date are very close in to the stars they orbit. Granted, this is an ease of detection result, but even so we now know that a high percentage of star orbiting planets are in relatively tight orbits. If it is certain that Mercury and Venus will be toast then a great many of the confirmed exoplanets will be as well :!:

neufer wrote:

BDanielMayfield wrote:
Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

I doubt that anyone can answer that particular question.

For all we know most planets may be roaming free in interstellar space.

BDanielMayfield wrote:

neufer wrote:

BDanielMayfield wrote:
Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

I doubt that anyone can answer that particular question.

For all we know most planets may be roaming free in interstellar space.

Of course the question is hard, and impossible to answer precisely, but I wouldn't think that reasonable estimates couldn't be obtained. And yes, most planets may indeed be free roamers, and their destruction rate would be extremely low. But if almost all stars have planets, and if the majority of them are close in, and if most stars go through the Red Giant phase, then it follows that planetary destruction is a regular occurrence.

Chris Peterson wrote:

BDanielMayfield wrote:

Chris Peterson wrote: I think it is likely that the planet formation rate greatly exceeds the planet destruction rate, and will remain so until the planet formation rate reaches zero (at which point planets will occasionally be destroyed, but that will be a very rare thing). There is good reason to think that our Sun has already created hundreds of planets, the majority of which are no longer part of our system and which are unlikely to ever be destroyed.

I think you are underestimating the planet destruction rate. Consider that the great majority of exoplanets found to date are very close in to the stars they orbit. Granted, this is an ease of detection result, but even so we now know that a high percentage of star orbiting planets are in relatively tight orbits. If it is certain that Mercury and Venus will be toast then a great many of the confirmed exoplanets will be as well

I think you are underestimating the planet formation rate. There is good evidence suggesting that most of the planets created in stellar systems are ejected very early. If so, most of the planets in the Universe are not orbiting stars, and the vast majority of these will never be destroyed.

BDanielMayfield wrote:

neufer wrote:

BDanielMayfield wrote:
Since planet formation is a by-product of star formation, simple logic suggestes that the maximum number of planets any given galaxy contains would be reached at some point after the galaxy's star formation ability wanes. This would be at the time when the planet formation and destruction rates would be equal. Has the Milky Way reached such a point yet?

I doubt that anyone can answer that particular question.

For all we know most planets may be roaming free in interstellar space.

Of course the question is hard, and impossible to answer precisely, but I wouldn't think that reasonable estimates couldn't be obtained. And yes, most planets may indeed be free roamers, and their destruction rate would be extremely low. But if almost all stars have planets, and if the majority of them are close in, and if most stars go through the Red Giant phase, then it follows that planetary destruction is a regular occurrence.

• Most stars DO NOT go through the Red Giant phase:

https://en.wikipedia.org/wiki/Red_dwarf wrote:
<<Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way. Because of the comparatively short age of the universe, no red dwarfs exist at advanced stages of evolution.

Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare. Microlensing surveys indicate that long-orbital-period Neptune-mass planets are found around one in three red dwarfs. Observations with HARPS further indicate 40% of red dwarfs have a "super-Earth" class planet orbiting in the habitable zone where liquid water can exist on the surface. Computer simulations of the formation of planets around low mass stars predict that Earth-sized planets are most abundant, but more than 90% of the simulated planets are at least 10% water by mass, suggesting that many Earth-sized planets orbiting red dwarf stars are covered in deep oceans.>>

BDanielMayfield wrote: And yes, most planets may indeed be free roamers
Bruce

Ouch - well, good thing
it wasn't a planet...

Ann wrote:

BDanielMayfield wrote: And yes, most planets may indeed be free roamers
Bruce

Ouch - well, good thing
it wasn't a planet...

That's why it's good that the Universe is a big place. Imagine the Earth getting hit by orphan planets on a regular basis.

neufer wrote:

BDanielMayfield wrote:... if most stars go through the Red Giant phase ...

• Most stars DO NOT go through the Red Giant phase:

https://en.wikipedia.org/wiki/Red_dwarf wrote:
<<Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way. Because of the comparatively short age of the universe, no red dwarfs exist at advanced stages of evolution.

Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare. Microlensing surveys indicate that long-orbital-period Neptune-mass planets are found around one in three red dwarfs. Observations with HARPS further indicate 40% of red dwarfs have a "super-Earth" class planet orbiting in the habitable zone where liquid water can exist on the surface. Computer simulations of the formation of planets around low mass stars predict that Earth-sized planets are most abundant, but more than 90% of the simulated planets are at least 10% water by mass, suggesting that many Earth-sized planets orbiting red dwarf stars are covered in deep oceans.>>

Red giants are evolved from main-sequence stars with masses in the range from about 0.3 M☉ to around 8 M☉.

Chris Peterson wrote:

BDanielMayfield wrote:
And yes, most planets may indeed be free roamers

Ann wrote:
That's why it's good that the Universe is a big place.
Imagine the Earth getting hit by orphan planets on a regular basis.

Heck, getting hit is no big deal. Bam and it's all over. It's the near misses that are really painful, where our planet gets shifted into a new orbit.