# Jupiter/Saturn's fate after Sun goes red giant and planetary nebula?

The solar wind contributes a very small amount of matter to the gas giants. As the sun approaches the red giant phase, the solar wind increases significantly. 10% of the sun's mass lost as solar wind over its lifetime, which is equal to 100 Jupiters in mass. After the red giant phase the sun releases the outer, mostly hydrogen, outer layer in the form of the planetary nebula. The planetary nebula is about 50% of the mass of the sun, which is equal to 500 Jupiters in mass, the remaining 40% of the sun will be left as the white dwarf.

After all this additional mass, most of which is hydrogen, is added to the gas giants how massive would they be and would any of them reach brown or red dwarf status?

Smallest brown dwarf is 13 Jupiters in mass, which is able to fuse deuterium. Smallest red dwarf is at 75 Jupiters in mass, which can fuse hydrogen.

• I've often wondered this myself. Their orbits would likely change too, perhaps moving a fair bit further from the sun as the sun lost mass. Commented Sep 17, 2017 at 2:15
• I don't think that even if the sun lost 10% of its mass that a substantial amount would be accumulated by the gas giants (consider the surface area of a sphere of 5AU/ not to mention that most flies right by). I think userLTK is correct above, however. Commented Sep 18, 2017 at 22:51
• I will clarify my question above, the 10% is only lost due to the solar wind during the sun's lifetime. The planetary nebula is more like 50% of the mass of the sun. Commented Sep 19, 2017 at 12:17
• I did a little math just for fun. Take a cross section of the magnetosphere of Jupiter (to the "terminator") to be PI x (120R(J))2 = 2.2 x 10E14 km2. Now take the surface area of a sphere at 5.2AU = 7.65 x 10E18 km2. This ratio is about 2.9 x10E-5. If the sun shed half of its mass (or about 10E30 kg) and all that encountered Jupiter's magnetosphere was captured, this captured amount would be about 2.9 x 10E25 kg. This value is about 1.5% of the mass of Jupiter. Commented Sep 21, 2017 at 4:41
• So maybe 5% is added due to lifetime solar wind and comet/asteroid impacts. Then assuming the orbit of Jupiter picks up more mass than you list since the nebula is likely to have some thickness for Jupiter to pass through, though the actual orbit of Jupiter is likely distinctly further by then anyway, causing a lower density to be swept up. Well I thought I was on to something. So unless some super advanced species decides to play sweep up a stars worth of planetary nebula and make a new smaller star in orbit of our future white dwarf it will definitley not be happening naturally. Commented Sep 21, 2017 at 15:20