This picture shows the magnetic field around Jupiter.
Click on image for full size
Windows to the Universe original artwork
Magnetic Fields Near Planets
A magnetometer is an instrument for measuring magnetic fields. Many spacecraft carry magnetometers to measure the magnetic fields around planets. When a spacecraft makes those measurements, what
do the measurements tell us?
The planet might have one big magnetic field covering the whole planet. Earth does, which is why we can use compasses to figure out which way is North. Mercury, Jupiter, Saturn, Uranus,
and Neptune all have global magnetic
fields too. Each of those planets has an area inside it that is a good conductor
of electricity. Their magnetic fields are caused by the flow of electricity in
The planet might have smaller magnetic fields around part of the planet. Maybe the planet had a strong magnetic field when it was young. Some of the planet's rocks might still have that magnetic field "locked into" them. Mars and Earth's
Moon have magnetic fields locked into their rocks. A magnetometer might also show the location of large deposits of ores such as iron. Ore deposits could even be the remains of an asteroid that struck the planet!
The spacecraft also might detect magnetism caused by the solar wind or the Sun's magnetic field. The Sun's magnetic field is very strong. The spacecraft's magnetometer might detect the Sun's field even when the spacecraft is near a planet. Charged particles from the solar wind can also become trapped within a planet's magnetosphere.
Particles moving around in the magnetosphere can also produce magnetic fields.
Finally, the magnetic field detected by a spacecraft might have two or more causes. For example, let's look at Earth. The magnetic field near Earth is partly caused by Earth's overall magnetic field, by charged particles racing around Earth's magnetosphere, and by other factors.
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, ranging from seismology
, rocks and minerals
, and Earth system science
You might also be interested in:
The force of magnetism causes material to point along the direction the magnetic force points. Here's another picture of how this works. This picture shows where the magnetic poles of the Earth are to...more
The Earth has a dipole magnetic field. This is when magnetic field lines point in a direction out of the South Pole and into the North Pole. Planets can also have quadrupoles (4 poles) and octupoles (8-poles)....more
The Earth has a magnetic field with north and south poles. The magnetic field of the Earth is surrounded by the magnetosphere. The magnetosphere keeps most of the particles from the sun, carried in solar...more
Mercury is the only inner planet other than the Earth that has a significant magnetic field (220 nT). This field, along with the planet's high density and small size relative to the Earth, indicates that...more
Jupiter's magnetosphere is very special. It is the biggest thing in the entire solar system. Not only is it big enough to hold all of Jupiter's moons, but the sun itself could fit inside. It goes all...more
Saturn's magnetosphere is not as big as Jupiter's, but it is still pretty big. It is big enough to hold all of Saturn's moons. The shape of the magnetosphere is affected by its size. The shape is also...more
The magnetosphere of Uranus is medium sized, but still much bigger than the Earth's. It holds all of Uranus' moons. It is probably made in the middle of the planet, and with ice, rather than with iron...more