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Is Jupiter a failed star?

Jupiter is the largest planet in our solar system and has many star-like qualities, leading some astronomers to wonder if it is actually a “failed star” that did not have enough mass to ignite nuclear fusion in its core. While Jupiter shares some similarities with stars, there are important differences that show it is a true gas giant planet.

Quick Answers

Here are quick answers to some common questions about whether Jupiter is a failed star:

Is Jupiter a star? No, Jupiter is classified as a planet, not a star. It does not produce any energy through nuclear fusion like stars do.

Could Jupiter become a star? No, Jupiter does not have nearly enough mass to ever become a star. Jupiter would need to be at least 80 times more massive to fuse hydrogen.

Does Jupiter emit light like a star? Jupiter reflects sunlight like the other planets, but does not emit light through internal fusion like stars do.

Why is Jupiter sometimes called a failed star? Jupiter shares some physical and chemical properties with stars, including composition, weather patterns, and strong magnetic field. But the similarities end there.

What key differences make Jupiter a planet and not a star? Jupiter does not have enough mass to create the core pressures and temperatures needed to fuse hydrogen into helium like a star.

Jupiter’s Star-Like Qualities

So why has Jupiter often been termed a “failed star” if it does not meet the criteria to actually be considered a star? Here are some of Jupiter’s stellar qualities that contribute to this misnomer:

  • Jupiter is made primarily of the gases hydrogen and helium, the same composition as stars.
  • Jupiter radiates more energy than it receives from the Sun due to its hot interior, a property shared with stars.
  • The planet has an enormous magnetic field, the strongest of any planet in our solar system.
  • Jupiter has a system of rings and over 75 moons orbiting it, more like a miniature solar system.
  • Storms and weather patterns on Jupiter like the Great Red Spot are similar to those observed on stars.

With these stellar qualities, one can see why Jupiter is sometimes mistakenly referred to as a failed star. But the planet lacks the most fundamental attribute of stars – the ability to produce energy through nuclear fusion.

Why Jupiter is Not a Star

Despite Jupiter’s star-like features, the planet is fundamentally different from stars in a few key ways:

  • Not enough mass – Jupiter is more massive than any other planet, but with 318 times the mass of Earth, it does not have nearly the mass of even the smallest stars. It would need at least 80 times its current mass to have enough pressure in its core to fuse hydrogen atoms together.
  • No nuclear fusion – The cores of stars fuse lighter elements into heavier ones, releasing enormous amounts of energy. Nuclear fusion requires extremely high temperatures and pressures. But Jupiter’s core produces no nuclear energy, only radiating leftover heat from its formation.
  • Does not emit light – Stars like our Sun shine due to the light emitted from nuclear reactions. Jupiter simply reflects light from the Sun like the other planets. It does not produce any visible light of its own.
  • No stellar classification – Stars are classified by features like mass, temperature, and luminosity. But Jupiter fits into the distinct category of gas giant planets, with different defining characteristics.

So while Jupiter shares some surface-level similarities with stars, it lacks the fundamental ability to produce energy through fusion that sets stars apart from planets.

Could Jupiter Become a Star?

Since Jupiter is often considered a “failed star”, could there be any way for the planet to gain enough mass in the future to become an actual star? While it may seem plausible, Jupiter becoming a star is essentially impossible for these key reasons:

  • Jupiter is not massive enough to ever fuse hydrogen or heavier elements, even if more mass were added.
  • The planet is not close enough to the Sun to accumulate more matter through gravitational attraction.
  • Jupiter does not have enough gravity to draw in and acquire more mass on its own.
  • The Sun will expand into a red giant before Jupiter gains significant mass, likely engulfing the planet in the process.

Based on our understanding of Jupiter and stellar physics, there is unfortunately no scenario in which Jupiter could randomly start nuclear fusion and spring to life as a star. The conditions needed simply do not exist, no matter how much the planet resembles a star in some other aspects.

Comparison of Key Properties

This table summarizes some of the key defining characteristics of Jupiter vs. stars, demonstrating why the planet cannot be considered a “failed” version of these hot, fusion-powered celestial bodies:

Property Jupiter Stars
Mass 1.9 x 10^27 kg
(0.001 M☉)
0.08 – 150 M☉
Density 1.33 g/cm^3 0.7 – 100 g/cm^3
Temperature 128 K (-145 C) 2,000 – 40,000 K
Composition 90% hydrogen, 10% helium 70-90% hydrogen, 10-30% helium
Energy Source None, absorbed sunlight Nuclear fusion
Luminosity 0.026 L☉ 0.0001 – 10 million L☉

As the table shows, Jupiter may be large for a planet but it is dwarfed by even the smallest stars in mass, temperature, luminosity, and energy production through fusion. While both bodies are composed mostly of hydrogen and helium, the structural and functional differences between gas giant planets like Jupiter and stars are quite definitive.


While Jupiter shares some similar composition and properties with stars like strong magnetic fields, storms, and a mini “solar system” of moons, the planet lacks the mass and pressure in its core to create nuclear fusion that powers stars. Jupiter simply does not have the right physical conditions or mechanisms to be considered a “failed star”. The similarities are only skin deep. At its core, Jupiter is a gas giant planet with no chance of becoming a star, failed or otherwise.