can Jupiter turn into a star

[traveller]

Ok, this is a very amature question, but I am not trolling but please explain things in simple terms.
Jupiter does not have the critical size to become a star, even a brown dwarf (http://en.wikipedia.org/wiki/Brown_dwarf). However, once the Sun reaches the end of its life, it will most likely go into a red giant phase, ejecting a significant amount of matter into space (aka planetary nebula), beyond the orbits of earth and Mars.
Therefore, would it be possible for Jupipter's gravitational pull to absorb much of the ejected matter from the Sun (and matter from the inner planets), and, over time, evovle into a protostar or even a brown darwf?
Please, as stated above, I am looking for simple explanations (if that's possible).
:help::question::thanx:
Bo

[bojan]

I think not...
Ejecta from Sun will be expanding with relatively high speed, so it won't be possible for Jupiter to accumulate enough in a time period the material is nearby. Right now I am not sure about the exact total mass of the ejected material, but if I remember correctly, it is not that large at all, as only the outer layers of the Sun will be ejected.. so there will not be enough material for the scenario you are describing even if the capturing process is 100% efficient (and I feel it will be much less than 0.001%.
I will check the exact numbers later and come back (if someone else doesn't do it in the meantime)....)

[traveller]

Thank you, yes the amount of ejecta will be critical, as Jupiter will need approx 80 times of its current mass in order to become a brown dwarf, and even if we include ALL the mass of the inner four planets, it will still not amount to much.

[traveller]

A quick calculation demonstrates thus:
1. Sun= 1 Solar Mass (1 SM)
2. If ejecta is 10% of SM as sun goes into red gaint (0.1 SM)
3. Jupiter approx 1/1048 SM (0.000954 SM)
4. Brown dwarf as having 80 Jupiter mass or 80/1048 SM (0.0763 SM)
5. Therefore Jupiter needs another 79 times its current mass (0.0754 SM) to achieve brown dwarf status.
6. This would require Jupiter to have caputred 75.4% of the sun's ejecta. This is not very likely due to the orbit of Jupiter and the speed of ejecta.

Conclusion: Highly unlikely.

Assumption: Does not account mass of inner planets and their moons, asteriods etc should they be destroyed by the ejecta and somehow captured by Jupiter's gravity.

:thumbsup:

[ballaratdragons]

Bo, Jupiter DOES actually have the physical size to become a star.
But it doesn't have the MASS.

There are zillions of stars (mainly brown dwarfs) and some known Neutron stars that are smaller than Earth! But they have the Mass of many many Jupiters :thumbsup:

[mswhin63]

There is not enough mass to start a nuclear reaction. Once a reaction starts gravity compresses the star to it relative size.

[bojan]

Malcolm, it is actually the other way around:
First the (future) star collapses and shrinks because of gravity.. then the thermonuclear reaction eventually starts because of high enough temperatures an pressure and then the radiation pressure from the hot interior keeps the balance with gravity so the newborn star doesn't shrink any more.

[mswhin63]

Yeah got back on here when I realised I was wrong damn it :P. Although Jupiter does not have enough mass to start fusion.

[lone77star]

Some good points by Bojan. But even if the dying sun did eject enough material, Jupiter is an awfully tiny scoop and the sun would be sloughing it off in all directions.