The largest planet in the solar system is Jupiter, a gas giant so massive it outweighs all the other planets combined by a wide margin.
This article explains what makes Jupiter the biggest, how scientists measure planetary size, and why its scale still surprises astronomers.
What is the largest planet in the solar system?
Jupiter is the largest planet in the solar system.
It has the greatest mass, the widest diameter, and the largest overall volume of any planet orbiting the Sun.
When people ask this question, they usually mean one of three things: which planet has the most mass, which has the largest diameter, or which takes up the most space.
In all three cases, Jupiter is the answer.
How big is Jupiter compared with the other planets?
Jupiter is enormous by planetary standards.
Its diameter is about 86,881 miles (139,822 kilometers), which is more than 11 times wider than Earth.
In terms of volume, more than 1,300 Earths could fit inside Jupiter if it were hollow.
Its mass is even more striking.
Jupiter weighs about 318 times as much as Earth and contains more than twice the mass of all the other planets in the solar system combined.
That makes it the dominant planetary body in the system after the Sun.
- Earth: about 7,918 miles in diameter
- Jupiter: about 86,881 miles in diameter
- Jupiter’s mass: about 318 Earth masses
- Jupiter’s volume: about 1,321 Earths
Why is Jupiter so large?
Jupiter formed early in the history of the solar system, when the young Sun was surrounded by a cloud of gas and dust called the solar nebula.
In the colder outer regions of that disk, solid material could accumulate into a large core quickly.
Once that core became massive enough, it began pulling in large amounts of hydrogen and helium from the surrounding gas.
This process is one reason Jupiter grew much larger than the rocky planets closest to the Sun.
Mercury, Venus, Earth, and Mars formed from heavier elements and had less access to the light gases that make up Jupiter’s thick atmosphere.
Its composition matters
Jupiter is mainly made of hydrogen and helium, the same light elements that dominate stars.
Unlike Earth, it does not have a solid surface in the usual sense.
Instead, its atmosphere becomes denser with depth until it transitions into exotic layers of fluid and metallic hydrogen under extreme pressure.
That composition allows Jupiter to accumulate and retain much more material than smaller rocky planets.
Its strong gravity also helps it hold onto those gases over billions of years.
Is Jupiter a star?
No, Jupiter is not a star.
Although it is made mostly of hydrogen and helium, it does not have enough mass to trigger nuclear fusion in its core.
A star like the Sun needs far greater mass and internal pressure to begin fusing hydrogen into helium.
Jupiter is sometimes called a “failed star,” but that label can be misleading.
It did not nearly become a star in the scientific sense; it formed as a planet and remained one because it never reached the required mass threshold.
How do scientists measure the largest planet?
Astronomers use several measurements when comparing planets, and each one highlights a different aspect of size.
- Diameter: the distance across a planet through its center
- Volume: the amount of space a planet occupies
- Mass: the amount of matter in the planet
- Density: how tightly packed that matter is
Jupiter ranks first in diameter, volume, and mass among the eight planets.
Its average density is lower than Earth’s because it is mostly gas, but that does not reduce its status as the largest planet.
How does Jupiter compare with Saturn?
Saturn is the second-largest planet and is often mentioned alongside Jupiter because both are gas giants.
Saturn has a slightly smaller diameter than Jupiter, but it is less massive and less dense.
In fact, Saturn is so low in density that it would float in a giant enough body of water, at least in a simplified thought experiment.
Jupiter, by contrast, is far more massive and exerts a much stronger gravitational pull.
Both planets have rings, powerful storms, and dozens of moons, but Jupiter remains the largest by every major physical measure that matters for planetary comparison.
What features make Jupiter stand out?
Jupiter is not only the largest planet in the solar system; it is also one of the most dynamic.
Its atmosphere contains bands of clouds, high-speed jet streams, and giant storms, including the Great Red Spot, a massive storm system observed for centuries.
Jupiter also has a powerful magnetic field, intense radiation belts, and at least 95 known moons.
Four of those moons—Io, Europa, Ganymede, and Callisto—are the Galilean moons, first observed by Galileo Galilei in 1610.
Notable Jupiter facts
- Great Red Spot: a giant storm larger than Earth
- Moons: at least 95 confirmed natural satellites
- Magnetic field: the strongest of any planet in the solar system
- Rotation: one of the fastest, with a day lasting about 10 hours
Why does the largest planet matter in astronomy?
Jupiter plays an outsized role in the solar system’s architecture.
Its gravity influences asteroid paths, affects comet trajectories, and helps shape the environment of the outer solar system.
Because of its mass, it is often used as a reference point when studying planetary formation and orbital dynamics.
Jupiter also helps scientists understand how giant planets form around other stars.
Exoplanet research frequently compares distant gas giants to Jupiter because it is the clearest example of a massive planet in our own system.
Could another planet ever become larger than Jupiter?
Not within our solar system.
The planets already formed and settled into their current sizes billions of years ago.
While collisions can change a planet’s shape or surface, they are not expected to create a new planet larger than Jupiter in the solar system’s stable configuration.
In other star systems, however, astronomers have discovered planets that are similar in size to Jupiter and, in some cases, even larger in radius.
These objects are called exoplanets, and they help researchers study the limits of planetary growth.
Key facts to remember
- Jupiter is the largest planet in the solar system.
- It is the largest in mass, diameter, and volume.
- It is a gas giant made mostly of hydrogen and helium.
- It is not a star because it lacks enough mass for fusion.
- Its size and gravity strongly influence the solar system.
Quick answer for searchers
If you are asking what is the largest planet in the solar system, the answer is Jupiter.
It is the biggest planet by every major measurement and remains one of the most important objects in planetary science.