Is Jupiter bigger than the Sun?

No. Jupiter is the largest planet in the solar system, but it is much smaller than the Sun. The Sun’s diameter is about 10 times wider than Jupiter’s, and it contains more than 1,000 times Jupiter’s volume. Jupiter is massive for a planet, but tiny compared to a true star.

What is the difference between Jupiter and a star?

The key difference is nuclear fusion. Stars generate energy by fusing hydrogen into helium in their cores. Jupiter does not have enough mass to sustain fusion. Instead, it is a gas giant planet that radiates leftover heat from its formation and slow gravitational contraction.

Is Jupiter the closest planet to becoming a star?

Yes. Jupiter is the most massive planet in the solar system and came closer than any other planet to reaching stellar mass. However, it would still need to be about 80 times more massive to ignite sustained hydrogen fusion and qualify as a true star.

What would happen if Jupiter became a star?

If Jupiter had somehow become massive enough to ignite fusion, the solar system would look very different. Earth would likely experience extreme gravitational disruption, altered orbits, and potentially unstable climate conditions. However, Jupiter lacks the mass required for this scenario, so it remains a stable gas giant.

Is Jupiter a Failed Star? Why It Never Became a Sun

By Karin Lehnardt, Senior Writer—Reviewed for accuracy by the FactRetriever editorial team

Published February 22, 2026

What if our solar system once had the chance to host two suns? Jupiter is so massive, so powerful, and so star-like that astronomers have long asked a provocative question: Did it almost ignite? It’s made of the same ingredients as the Sun. It gives off its own heat. It dominates everything around it. And yet… it never began to burn. Some people call Jupiter a “failed star," a cosmic almost. A giant that came close to lighting up the sky but fell short of the mass needed to spark nuclear fusion. But how close was it, really? Would Earth even exist if Jupiter had ignited? Could it still become a star someday? And what actually separates a massive planet from a true sun? The answers reveal just how narrow the line is between planets and stars — and why Jupiter may be far more important unlit than it ever would have been blazing.

Why Is Jupiter Called a Failed Star?

Jupiter is called a failed star because of its size and composition. It contains more mass than all the other planets combined and is primarily made of hydrogen and helium, the same elements found in stars.
However, it lacks the mass required to ignite sustained hydrogen fusion in its core._[1]
How Massive Would Jupiter Need to Be to Become a Star?

Jupiter would need to be about 80 times more massive to sustain hydrogen fusion and become a true star.
At roughly 13 times its current mass, Jupiter could potentially qualify as a brown dwarf, an object that can fuse deuterium but cannot sustain long-term stellar fusion.
At its current size, Jupiter remains a gas giant planet._[2]

Jupiter is not a failed star fact and trivia

Jupiter is the largest planet in our solar system, often called a "failed star" because it contains mostly hydrogen and helium but lacks the mass for nuclear fusion

Does Jupiter Produce Heat Like a Star?

Yes, Jupiter radiates more heat than it receives from the Sun, but not through nuclear fusion.

Its heat comes from slow gravitational contraction. As Jupiter gradually compresses under its own gravity, it releases thermal energy into space. This process is called Kelvin-Helmholtz contraction.
It is not the same as stellar fusion._[3]
What Is a Brown Dwarf?

A brown dwarf is an object too massive to be a planet but not massive enough to sustain hydrogen fusion like a star.

Brown dwarfs can briefly fuse deuterium, but they lack the core pressure and temperature required for sustained stellar energy production.
Jupiter falls well below this mass threshold._[3]
Why Didn’t Jupiter Become a Star?
Jupiter did not become a star because most of the solar system’s mass went into forming the Sun during its early formation.
When the protoplanetary disk formed 4.6 billion years ago, Jupiter accumulated a large amount of gas, but not enough to reach the fusion threshold.
There simply wasn’t enough material available in its region to grow that large._[3]
Could Jupiter Ever Ignite in the Future?"

No. Jupiter cannot become a star in the future.

To ignite hydrogen fusion, it would need to gain dozens of times its current mass. There is no source of material in the modern solar system capable of increasing its mass to that extent.
Its planetary status is permanent._[3]

Jupiter's immense gravity redirects asteroid and comets, which protects Earth and shapes the architecture of our solar system

How Jupiter Shapes the Solar System Instead

Although Jupiter never became a star, it plays a crucial role in stabilizing the solar system.

Its immense gravity:

🎯 Redirects comets

🎯 Influences asteroid belts

🎯 Alters planetary orbits

🎯 Reduces potential impacts on inner planets

🎯 Without Jupiter, the inner solar system, including Earth, would likely experience more frequent catastrophic collisions.
For a broader overview of Jupiter’s size, storms, moons, and influence, explore our complete guide to fascinating Jupiter facts._[1]
Final Answer: Is Jupiter a Failed Star?

Scientifically, no.

Jupiter is a gas giant planet that lacks the mass required for nuclear fusion. It sits below the threshold that separates planets from brown dwarfs and far below the mass needed to become a true star like the Sun.
The term “failed star” is a popular nickname, not a scientific classification._[2]