Jupiter’s Magnetosphere and Hill Sphere: Solar System without Jupiter

From the lecture Series: A Field Guide to the Planets

By Sabine Stanley Ph.D., John Hopkins University

Jupiter’s magnetosphere is the gas giant itself. However, what makes it significant is not its vastness, but the impact it has on the whole solar system: it’s like a glue, holding the planets together. The solar system would simply fall apart without Jupiter and its powerful magnetic effect.

Juno spacecraft in it's polar orbit around Jupiter with Jupiter's aurora visible.
Jupiter’s magnetosphere and its gravitational force keep our Earth and other planets safe from many collisions. (Image: Raymond Cassel/Shutterstock)

Solar Wind and Jupiter’s Magnetosphere

Jupiter’s magnetosphere is significantly huge as it has a very strong magnetic field and is over five times farther from the Sun compared to Earth. Jupiter’s magnetosphere extends about 5,000,000 kilometers on its sun-facing side, and more than 100 times further on the other side. Saturn is as far away from Jupiter as is the Sun, but the magnetosphere reaches Saturn’s’ orbit. What happens in this gigantic magnetic bubble?

A magnetosphere shields its planet from the solar wind, but when it is too strong, charged particles can be trapped and accelerated along the powerful magnetic field lines. Thus, high-energy particles and intense belts of radiation are created. On Jupiter, the radiation is similar to the Van Allen radiation belts surrounding Earth, but 20 million times stronger. The extremely high radiation makes it very difficult to send spacecraft close to Jupiter.

A comparison between Earth and Jupiter on a clean black background.
As Jupiter is significantly larger than Earth, so is its magnetosphere and Hill sphere. (Image: Tristan3D/Shutterstock)

Jupiter has the most powerful auroras in the solar system: from visible light to X-rays 1000 times stronger than Earth’s aurora. What happens at the core of this gas giant that creates such a strong magnetic field around?

Learn more about Uranus: A water world on its side.

The Core of Jupiter

What lies at the center of Jupiter is a direct result of how it was formed. Thus, there are a few hypotheses on the matter. Is it a thoroughly gas planet with hydrogen and helium at different phases and a bit of heavier elements? Or does it have a dense rocky and icy core, surrounded by layers of hydrogen and helium? The Juno mission found an answer.

Jupiter is formed in either of the two following ways:

  • It started as a rocky planet and, due to its cooler location in the solar system, slowly turned into a protoplanet by absorbing the condensed material available. Later, it grew big enough to gravitationally attract the hydrogen and helium around and turn into the gas giant we see today. The planet structure under these conditions should be layered.
  • There was no rocky core, but enough hydrogen in the solar nebula while the planets were forming, causing perturbations in the movement of the gas. Thus, the gas became massive enough to have gravity and attract other gas around. In this case, Jupiter must have been much more homogeneous.

However, Jupiter is neither layered nor homogeneous. Rather, it has a much larger, more diluted mixture of heavy elements, hydrogen, and helium at the core, called ‘Jupiter’s fuzzy core’.

It is not clear how the fuzzy core was formed, but it could be that it dissolved from a small and dense core. Another possibility is that the heavier elements are somehow precipitating out of the homogeneous planet and sinking toward the center. Regardless of how it was formed, its impact is undeniable.

This is a transcript from the video series A Field Guide to the Planets. Watch it now, on The Great Courses Plus.

Jupiter’s Hill Sphere

Jupiter has an enormous gravitational sphere of influence, known as a Hill sphere. Just like Jupiter’s magnetosphere, its gravitational force also extends far into space. Hill sphere is defined as the distance where Jupiter’s gravitational attraction gets stronger than the Sun’s, for objects orbiting the Sun. The Hill sphere of Jupiter extends 55 million kilometers around the planet.

A picture showing Jupiter.
Jupiter’s Hill sphere reaches 55 million kilometers around the planet and sometimes changes the orbit of smaller objects. (Image: NASA images/Shutterstock)

The massive Hill sphere is due to Jupiter’s enormous mass and its significant distance from the Sun and its gravity. Despite what it may seem, Jupiter does not have the biggest Hill sphere in the system. Neptune has the largest, with a radius of 87 million kilometers. However, as Jupiter moves faster than the other giants further from the Sun, it is more likely for other moving objects to collide with it.

Objects in the solar system can be affected in two ways by Jupiter’s Hill sphere:

  • Their orbit is changed, and they start orbiting Jupiter, perhaps the same way Jupiter attracted many moons.
  • They are forced into new regions of the solar system, such as the comets, which led to the inner solar system by Jupiter’s gravitational force.

Learn more about Jupiter’s planetlike system of moons.

Jupiter, the Gatekeeper

Without Jupiter, the inner solar system would lose a gatekeeper. Further, many objects are attracted away from the Earth and other inner planets due to Jupiter’s force, and many are attracted inward because of it.

Without Jupiter’s gravity, the asteroids in the belt would possibly have coalesced into another planet. The Trojans, the thousands of known asteroids concentrated at the L4 and L5 Lagrange points along Jupiter’s orbit, are another result.

Lucy, a NASA mission scheduled for October 2021, is supposed to visit six Trojans and reveal their mysteries. What is known of them is that they are under the strong impact of Jupiter’s magnetosphere and gravitational force, like many other objects in the solar system.

Common Questions about Jupiter’s Magnetosphere

Q: How big is Jupiter’s magnetosphere?

Jupiter’s magnetosphere is about 5 million kilometers wide on average. It is one of the largest structures in the solar system, 150 times wider than Jupiter itself and nearly 15 times wider than the Sun.

Q: Does Jupiter have a magnetosphere?

Not only does Jupiter have a magnetosphere, but it is also one of the grandest things in the solar system. Jupiter’s magnetosphere extends millions of kilometers around it, is at least ten times stronger than Earth’s, and creates significant auroras.

Q: How many poles does Jupiter’s magnetosphere have?

Jupiter’s magnetosphere has two south poles, which make it different from all other known magnetospheres in the solar system.

Q: Which planet has the strongest magnetosphere?

Jupiter’s magnetosphere is the largest and strongest of all in the solar system. It is so significant that without it, the whole solar system would be affected, and some bodies would not stay in place.

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