In the classic science-fiction film 2010: The Year We Make Contact, an alien intelligence causes Jupiter to contract so much that nuclear reactions begin at its center. As a result, Jupiter becomes a star like the Sun. Is this possible in principle? Explain your answer.

Stellar nucleosynthesis refers to the process by which stars create heavier elements from lighter ones through nuclear reactions. This remarkable process takes place in the cores of stars and can span the production of elements from helium all the way to iron in massive stars. The journey of element formation begins when a star reaches sufficient temperature and pressure for hydrogen atoms to overcome their electrostatic repulsion and fuse together, creating helium in a series of reactions collectively known as the proton-proton chain.

For heavier stars, as the star evolves, it moves on to fuse helium into carbon, and then additional elements in processes like the carbon-nitrogen-oxygen (CNO) cycle and the triple-alpha process. These nuclear reactions release incredible amounts of energy, which is why stars shine so brightly. It is also these reactions that contribute to the 'shine' and stability of a star over millions to billions of years, as they balance out the inward pull of gravity. After a star exhausts its nuclear fuel, it may eject some of these newly formed elements into space, where they can eventually become part of new stars and planets.

Gravitational collapse is the mechanism by which star formation begins. It occurs when an interstellar gas cloud, mainly composed of hydrogen and helium, becomes unstable and starts to fall inward under its own gravitation. Several conditions need to be met for collapse to commence, such as the cloud reaching a critical density and temperature, and the effects of external forces like nearby supernova explosions or collisions with other clouds.

The collapse leads to an increase in density and temperature at the core of the cloud. This acts as a precursor to a star's birth. Without gravitational collapse, the gas would remain too diffuse, and nuclear fusion – the star's powerhouse – could not occur. Also, the mass of the resulting celestial body plays a crucial role in what kind of object forms – whether a star, a brown dwarf, or simply a denser gas cloud.

Nuclear fusion is the process that powers stars and produces the heat and light that we observe. In the cores of stars, where the temperatures and pressures are extremely high, atoms can overcome their natural repulsion to fuse together. The most common fusion process in stars is the fusion of hydrogen atoms to form helium – this process is known as the hydrogen fusion or proton-proton chain.

Different fusion processes occur at different stages of a star's life, depending primarily on its mass. For example, in the later stages of a massive star's life, fusion continues with heavier elements like carbon and oxygen. The star's ability to fuse elements heavier than hydrogen and helium depends on the temperatures achieved in its core. Since significant mass is needed to achieve the requisite core temperatures for fusion of heavier elements, low-mass stars like red dwarfs cannot undergo this process, limiting them to fusing hydrogen only.

The mass of celestial bodies, such as planets and stars, is the fundamental attribute that dictates their fate and characteristics. A body's mass determines its gravitational force, which influences its ability to attract and hold onto the surrounding matter. For star formation, mass is crucial – it dictates not only the star's potential to ignite nuclear fusion but also its lifespan and the types of reactions it will undergo.

The mass necessary for a star to sustain fusion is termed the 'minimum stellar mass,' and objects below this threshold are known as brown dwarfs or 'failed stars' because they do not sustain regular fusion reactions. On the other hand, massive stars have shorter lifespans but are hot enough to fuse heavier elements, leading to a greater diversity of chemical elements. When considering celestial bodies, mass also impacts the body's structure, surface gravity, and its interaction with other celestial bodies, such as in forming planetary systems or in the outcomes of stellar collisions.