What happens to the planets as the sun dies?

[LKD]

I was thinking on a different article, and tangented from there to thinking on the sun's life cycle. As it burns up fuel, it looses mass.

Initially this wouldn't matter much at all to the solar system, but with both solar wind, and the orbiting speed of planets, at some point the loss of mass should break the gravitational pull, and the planets would slowly begin to be flung off into the deepest space, much like the moon is slowly loosing it's distance from Earth.

Would there somewhere out there in places where solar systems have long since died to supernovas be planets wandering aimlessly through vacuum? Is this totally off base?

 

[weeman]

Rogue (wandering) planets are not at all an absurd idea. They have often been discussed by astronomers.

 

[MeteorWayne]

The sun will lose (not loose) some mass, but not enough for the planets to escape the solar system.

 

[theridane]

In order for mass loss being responsible for an ejection of a planet the star's mass would need to drop to a half or less - only then would the former circular velocity become the "new" star's escape velocity (at any distance within its SOI). I'm no astronomer, but as an occupant of a planet in that system I'd be more concerned with half the sun floating by me than with the whole rogue planet thing.

A more likely scenario involves a strong attractor (a black hole, a rogue star, a star during a galactic collision etc.) floating through the star system, perturbing the orbits of everyone present.

 

[LKD]

Yes, I know Wayne, but one picks up bad inexplicably habits over the years, and editing them out is sometimes overlooked.

Thank you for the reply all.

I am curious, for my own clarity if you don't mind me asking, why even a 20% loss, a high end estimate I am certain, from solar winds and nuclear consumption, would have no fatal bearing on the orbit of a planet? Considering that such an amount would be a planet two hundred times that of Jupiter. It seems to me that that would be counter intuitive.

 

[dryson]

Initially this wouldn't matter much at all to the solar system, but with both solar wind, and the orbiting speed of planets, at some point the loss of mass should break the gravitational pull, and the planets would slowly begin to be flung off into the deepest space, much like the moon is slowly loosing it's distance from Earth.

The rest of the planets might not be affected but any drop in solar activity past 5% we would see the climate here on Earth become colder and colder as the Sun slowly died. Eventually it would get so cold that all water would freeze to to within maybe 100 feet of the bottom of the ocean where the lava jets would keep the water at a rather pleasant temperature for the creaturs swimming at those depths but all life on the surface would cease to exist and become entombed in an icy graveyard.

 

[PiotrSatan]

Initially this wouldn't matter much at all to the solar system, but with both solar wind, and the orbiting speed of planets, at some point the loss of mass should break the gravitational pull, and the planets would slowly begin to be flung off into the deepest space, much like the moon is slowly loosing it's distance from Earth.

The rest of the planets might not be affected but any drop in solar activity past 5% we would see the climate here on Earth become colder and colder as the Sun slowly died. Eventually it would get so cold that all water would freeze to to within maybe 100 feet of the bottom of the ocean where the lava jets would keep the water at a rather pleasant temperature for the creaturs swimming at those depths but all life on the surface would cease to exist and become entombed in an icy graveyard.

Actually it is said that Earth and all closer to sun planets will explode. I doubt Solar System will be able to support Jupiter too, so it and it moons might become a rogue planet unless a close-in of other sun will take it away among with the other giants.

 

[Jeph246]

The inner planets wouldn't explode, they would vaporize, because as the sun loses hydrogen and there's a tiny bit less gravity, the outer layers of the sun's atmosphere would expand to consume Venus, and even possibly Earth.

 

[SpaceTas]

Some points:

The mass loss up to the red-giant and helium flash stages from the solar wind is tiny compared to the mass of the Sun. ie it is about 10^-14 solar mass per year. Mass loss due to energy conversion is even smaller. So any changes in orbits will be tiny.

Stellar models have the sun slowly increasing in luminosity as it ages.

In the first giant branch stage (hydrogen shell burning); the sun will grow in size, cool and become more luminous. It should expand to beyond the orbit of Venus. There won't be much mass change, so Mercury and Venus will orbit inside the Sun, slowly getting vaporized (Temperatures about 4500 K). Earth survives but without atmosphere ... Other planets you can do rough calcs and speculate.

Mass loss rate goes up (high end 10^-4 solar mass per year) but still not enough to have major effect on orbits over short time-span of red giant phase..

Through a 2-3 intermediate steps, the Sun will get to the point of fusing Helium into Carbon. This reaction is extremely sensitive to temperature, so the sun becomes unstable. The pulse(s) of energy from a small temperature rise(s), a huge energy output rise(s), will fairly gently blow off the outer atmosphere of the sun to form a planetary nebula, while the cor becomes an exposed hot white dwarf that very slowly cools.

Now the amount of mass ejected in the planetary nebula is significant 0.2 to 0.6 solar mass. Because the models are complex and very sensitive to temperature the amount of mass ejected is hard to estimate. If the mass is less than 0.5 solar mass (1/2 mass) then the planets will move out but not escape. If more than 1/2 the Sun is expelled the planets will escape the lower mass sun. You can verify this half rule by comparing the new (lower mass) escape velocity with the old orbital velocity. The planets will spiral out, not "zip" out in a straight line.

The fastest timescale for the orbital changes would happen as the atmosphere was ejected. The average expansion velocities of young planetary nebulae is 20 km/s (Gussie G.T. & Taylor A.R., 1994, PASP 106 500-507) ie 86 days per AU or 11 years to Pluto. The changes won't even be this fast because all the mass is not ejected as a thin shell. So time scale for the loss of planets (if it happens; ie high ejected mass) will be years.

 

[Smersh]

... Would there somewhere out there in places where solar systems have long since died to supernovas be planets wandering aimlessly through vacuum? Is this totally off base?

I saw on a science website somewhere a while back (might even have been here in an article at Space.com, not sure) that there are thought to be entire solar systems out in the middle of nowhere that are not a part of any galaxy. The article was accompanied by an artist's impression of the view of a parent star from one of its planets, with no other stars in sight, only distant galaxies. I just did a search but unfortunately can't find the article now.

So if that's possible then I guess rogue planets would be possible as well. As to what causes them to be like that though I don't think is known, but perhaps planets that have somehow survived the death of their original parent star might be one explanation for solitary planets with no parent star.

 

[LKD]

Oh, I see. Thank you for the extended detailing of the process, that helps very much.

That article would be quite interesting to read, I will have to keep an eye out for it. The situation reminds me somewhat of Dark City.

 

[EarthlingX]

Just one, slightly off topic question :
- why would coalescing dust in the interstellar space require a star ?

Star is just a bit more of dust and gas in the same gravity well, or is there a known limit, how small can a thing be for the gas and dust to start gathering into something bigger, if temperature of the gas allows it ?

What's more, i think there is a relation between the size of a gravity well and it's commonality, or to put differently : as things get smaller, their number rises, from big to small, sort-of : galaxy cluster - galaxy group - galaxy - dwarf galaxy - star cluster - black hole - big stars - small stars - red dwarfs - planets - moons - asteroids - dust particles - gas, if i stop here.
I'm curious, how would this numbers look in a graph .. ?

I think, there are much, much more yet unseen things in the interstellar space than we dare to say, if not think, and intergalactic space is even more huge-ormous.

 

[neilsox]

Rogue planets were formed about 4.6 billion years ago in our solar system, when sling shot maneuvers accelerated some planets to faster than escape velocity. Most of them are likely still wandering about our galaxy. If there are 100 trillion of them in our galaxy one should pass though our solar system at century or so intervals. Since none have come by recently, there are likely less than 100 trillion rogue planets in our solar system. If one is presently approaching at 100,000 miles per hour and is presently 20 billion miles away, we will likely discover it soon, and it will be near by in 200,000 hours = about 21 years. A bit sooner as it will gain a little speed when it gets closer to the Sun. As the others posted, planets are typically not lost = ejected because a star lost several percent of it's mass. Possible exceptions are planets, if any, orbiting a light year or more from a star.
Likely most rogue planets approach at much less than 100,000 miles per hour/50,000 miles per hour, perhaps. Neil