Like the sun, Jupiter is composed predominantly of hydrogen & helium. But unlike the sun, it lacks the necessary amount to begin fusion, the process that fuels a star. Jupiter would need to be 75-80 times more massive than it is at present to be considered a star. If all of the planets in the solar system had formed as part of the gas giant, it still would not have sufficient mass. Still, by itself, Jupiter is 2 & 1/2 times larger than all of the other planets in the solar system combined.
This mission will be very dangerous for the probe. It will face large amounts of radiation, gravity and the largest magnetosphere in the solar system. No probe in history has come this close to Jupiter 6/27/16