Question: In the movie 2010:The year we made contact. Jupiter became a second sun. Is this possible? If so how will earth be affected?

Sam Vinko answered on 12 Mar 2012:

I’m afraid not. Jupiter is the largest planet in our solar system but its not heavy enough for fusion to take place. To understand this, recall how stars are formed: interstellar matter comes together under the force of gravity, which compresses it together. The more mass is available, the stronger the gravitational force will be. This force compresses the core of the system and heats it.

What happens then depends on the amount of matter available:

1) if the mass is below ~ 10 times the mass of Jupiter, you’ll have a planet
2) above ~ 15 Jupiter masses the core will be hot/dense enough to fuse deuterium (a Hydrogen isotope) and you’ll have a brown dwarf
3) if above ~60 Jupiter masses, the core can also fuse lithium (the third element on the periodic table)
4) if above ~80 Jupiter masses, the mass is finally sufficient to compress and heat the core to the point where it can start fusing hydrogen, and can be called a proper star! Our sun, in comparison, is about 1000 Jupiter masses.

So Jupiter is nowhere near massive enough to sustain fusion and be a star.