Can a Planet Become a Sun?

The idea of a planet turning into a star, like Jupiter becoming a sun in science fiction, is captivating. However, from the perspective of astrophysics, a planet will never transform into a star under any circumstances. This article explores the reasons why planets cannot become stars and the characteristics of objects that share some traits with both planets and stars.

Understanding Star Formation

Stars form from vast clouds of gas and dust that collapse due to gravity. This process is accompanied by nuclear fusion, which requires a significant amount of mass, typically at least 0.08 times the mass of the Sun (or 80 times the mass of Jupiter) to ignite reactions in their cores. Planets, on the other hand, do not possess the necessary mass or conditions to initiate this process.

The Impossible Transformation

While it's technically possible to consider all stars as having once been planetoids, the planets in our solar system are fundamentally different. They lack the mass and internal heat required to start nuclear fusion. For instance:

Brown Dwarfs

Brown dwarfs are objects that bridge the gap between planets and stars. These bodies are too massive to be planets but not massive enough to sustain hydrogen fusion like regular stars. They can fuse deuterium or lithium but don't reach the temperatures needed for hydrogen fusion. Thus, brown dwarfs have unique characteristics that are a hybrid of planets and stars.

Gas Giants

Planets like Jupiter and Saturn, known as gas giants, are composed predominantly of hydrogen and helium, similar to stars. However, they lack the necessary mass to achieve the conditions required for fusion. Despite their similarities, gas giants remain planets and cannot become stars.

Science Fiction vs. Reality

In the realm of science fiction, the line between planets and stars can be blurred. For example, in 2001: A Space Odyssey, Jupiter is described as a star-like body. However, in reality, the likelihood of a planet becoming a star is next to zero. Theoretical astrophysicists have concluded that a planet can be no bigger than about 10 times the mass of Jupiter to potentially become a star. The smallest theoretical mass for a star to support nuclear fusion is 0.07 or 0.08 solar masses. Smaller stars, therefore, are an impossibility for planets to become.

Thus, while planets cannot become stars in the traditional sense, objects like brown dwarfs and the idea that all stars were once planetoids provide an interesting blend of science and imagination. The quest for knowledge remains a driving force in understanding the intricacies of the universe.