The planet Jupiter is well known to be the largest planet in our solar system. She is so huge that there are even stars that are smaller than her. For example, the smallest known star of our galaxy is called EBLM J0555-57Ab and it has an average radius of 59,000 km, that is, it is just a little larger than Saturn and is more smaller than Jupiter which has an average radius of 69,911 km.
Despite its smaller size than Jupiter, the red dwarf, which is 600 light years from Earth, is the site of a hydrogen fusion reaction at its nucleus, a process that takes place at within the stars until they consume all their fuel. One can thus wonder why the planet Jupiter, with its size, is a planet and not a star .
According to scientists, the answer to this question is simple. Jupiter does not have enough mass to trigger the fusion reaction, that is to say to merge the hydrogen atoms into helium. We know that EBLM J0555-57Ab, even small in size, has a mass 85 times greater than that of Jupiter.
Far from being a star
Jupiter is sometimes called a failed star. But is the planet really close to being a star?
The first difference between a planet and a star is in the process of formation. Stars are born when an amount of material in an interstellar molecular cloud collapses due to gravity. During this phenomenon, the collapsed matter attracts even more material and forms a stellar accretion disk. In the center, the mass and the force of gravity increase more and more, so that the core is more and more compressed and the temperature keeps rising. At a certain point, the nuclear fusion reaction is set in motion.
From what we know, when the star has finished absorbing material, a large part of the accretion disk remains all around it, and it is from these remains that the planets are form. Scientists believe that the formation of gas giants like Jupiter begins when small pieces of icy rock and dust begin to clump together in orbit around the star using static electricity. At some point the pile is large enough and has a mass large enough on the order of 10 land masses to attract more and more gas. For Jupiter, the growth reached 318 earth masses and drew all the gas that was available. However, this mass was not sufficient to trigger the fusion of the hydrogen.
Thus, Jupiter is not really a failed star, unlike brown dwarfs which are cosmic objects lying halfway between planets and stars. Brown dwarfs are formed like normal stars, but their mass is not sufficient to initiate the thermonuclear reaction.
Similar to the Sun?
Even though it is not a star, Jupiter is still a heavyweight in the solar system. Its mass is indeed 2.5 times that of all the other planets combined. Where the gas giant is lacking is in terms of density. Its density is 1.33 g / cm 3 while that of the Earth is 5.51 g / cm 3 .
Jupiter also has some similarities with the Sun. Regarding the density, that of our star is 1.41 g / cm 3 , a value quite close to that of the gas giant. In terms of composition, the two objects are also almost similar. Relative to mass, the Sun is made up of 71% hydrogen and 27% helium and some traces of other chemical elements. For its part, Jupiter, in relation to its mass, is made up of 73% hydrogen and 24% helium.
Thus, we can say that Jupiter, from the beginning, could not have become a star. The giant planet is nonetheless a curiosity that has not yet finished revealing its secrets to us.