Is Jupiter A Failed Star? How Close Is The Giant Planet To Being A Second Sun In Our Solar System?

Jupiter is our solar system’s largest and most massive planet. Its temperatures and pressures are mind-boggling.

Its mass is 1.9 x 10²⁷ kilograms, nearly twice the combined mass of all the other planets in our system. Moreover, Jupiter’s atmosphere is made up primarily of hydrogen and helium which are the same elements that fuel our Sun.

In this line of thought, it’s understandable to wonder if Jupiter is a failed star. Also interesting is the question of whether Jupiter could become a star. This answer involves a deep dive into Jupiter’s composition and its formation history. 

As well as answering these questions, we’ll also take the fiction route to see how our solar system would have been and what might have happened if Jupiter were a star. Let’s go! 

Could Jupiter Have Been A Star? 

In a word, no, it couldn’t.

The way stars form is fundamentally different from how Jupiter formed, so calling it a failed star is misleading.

Composition 

Like our Sun, Jupiter primarily consists of hydrogen and helium. This suggests that the gas giant had formed at the same time as our Sun did. Because of these common elements and the fact that Jupiter remained a planet, it is often labeled as a failed star. 

However, despite its enormous size, Jupiter is not massive enough to turn into a star, which is why the word ‘failed star’ is a misnomer. We’ll come back to how much bigger it needed to be to ignite in a moment.

Formation History

Stars like our Sun are formed from the collapse under gravity of vast clouds of gas and dust. As it collapses, the cloud starts spinning to conserve angular momentum.

The material at the center of this spinning disc forms the star, and what is left forms a disk around the star. It is inside this disk that planets are created. 

Planets, including Jupiter, are formed from the collision of ice and rock planetesimals over time. Since this fundamentally different from how stars are created (i.e. from collapsing clouds of gas), Jupiter was never even on the path to becoming a star. 

That being said, it is worthwhile to note that any celestial body, when massive enough, can become a star. 

Why Jupiter is Not a Star

Becoming a star requires thermonuclear reactions to take place in the core of a celestial body. Igniting these reactions requires truly astounding levels of heat and pressure which could only be achieved in Jupiter if it was at least 80 times its current mass.

Although Jupiter is larger than the smallest stars, it falls short of becoming one itself. This is because it is mass and not size that is important. 

The fusion reactions at the heart of a star combine two atoms (generally two hydrogen nuclei fuse to form a helium nucleus, but heavier elements are used as the star ages and depletes its hydrogen supplies) and produce energy. It is this energy which is seen as the star’s light. 

Jupiter is simply not massive enough to contain this amount of pressure, there is not enough ‘stuff’ available to create the conditions for nuclear fusion to occur. If the gas giant were 80 times more massive than it is now, its mass would be just enough for fusion to begin. 

Is Jupiter a Sub-Brown Dwarf? 

No. Jupiter’s mass is not sufficient for it to be considered as a brown dwarf.

What is a Brown Dwarf?

A brown dwarf is a special kind of star. They have a lower mass and, consequently can only bring about the fusion of deuterium, an isotope of hydrogen. They also only liberate enough energy to be glow in the infrared area of the spectrum with very little visible light emitted.

Why Can’t Jupiter Become a Brown Dwarf Star?

At the moment, Jupiter is a gas giant. In our fictional journey to imagine Jupiter as a star, we will be making a couple of stops. 

First, we know that Jupiter will need additional mass to be on the way to becoming a star. If we keep adding mass to the point that the gas giant becomes anywhere between 13 to 75 times more massive, it will be called a brown dwarf. 

At this stage, Jupiter will be bigger than a planet and smaller than a real, small star and will still not be able to sustain fusion. So, as huge as Jupiter is, we’d need at least 14 more of them to create a brown dwarf.

As we keep adding more mass, Jupiter eventually becomes 80 times more massive than it is today. At that point, it will be a true stellar object, the smallest of which is a red dwarf.

To become a star similar to our sun, Jupiter will need 1,000 times more mass than it currently has!

Does Jupiter Have the Right Material to Make a Star? 

Jupiter has all the ingredients required to become a star.

After the Sun formed, Jupiter formed by consuming most of the leftover material. It now consists of all the right elements to form a star.

This table shows how closely Jupiter’s composition matches that of the Sun: 

Can Gas Giants Become Stars?

As we’ve discovered, gas giants that have enough mass and the right composition to kickstart and maintain nuclear fusion would be classified as stars.

The fundamental definition of a star is a celestial body that produces its own light through nuclear fusion, i.e. at least 13 times as massive as Jupiter. Below this, the pressures and temperatures are not high enough for fusion to occur.

The exact composition of the gas giant becomes important here.

In the case of Jupiter, theoretically adding more mass will ignite the gas giant into a star because Jupiter already has all the necessary hydrogen to fuse.

This may not be the case for every gas giant and will depend on the exact chemical composition. 

Are There Any Known Exoplanets Large Enough to Become Stars?

Exoplanets which are 15 to 75 times more massive than Jupiter are classified as brown dwarfs. Ones that are 80 times more massive are red dwarfs.

The table below shows of exoplanets we know of which are large enough to be brown dwarves.

What Would Happen to the Solar System If Jupiter Became a Star?

Simply put: Chaos!

Jupiter’s new role as a star would disrupt the delicate gravitational balance of the planets’ orbits, increasing the possibility that they might crash into each other or leave the solar system altogether.

If Jupiter became a red dwarf, nothing on Earth would be dramatically affected because Jupiter is four times farther away from Earth than the Sun. 

The only change that might be noticed is the increase in the number of asteroids from the asteroid belt that would have been disrupted because of Jupiter’s newly attained mass and gravity. 

At 1,000 times more mass, however, Jupiter will become a star like our Sun. This will disrupt the collective harmony of the current orbits of planets.

How events would unfold in that scenario is hard to predict, as you can see in the video below.

Summary

While Jupiter’s size might lead one into wondering about the gas giant’s future as a star, it is important to remember that it is the mass that is important, not size.

Celestial bodies smaller than Jupiter have become stars because they have enough mass to ignite thermonuclear reactions. 

Although Jupiter has all the ingredients to be a star, it is never going to transform into one without a tremendous injection of new material.

Which is good news for us, because we’ll continue enjoying viewing Jupiter in our skies for a long time to come.