On Earth, the magnetic field of our planet points only north, but in space, things are a bit more complex.
The compass, humanity’s primary navigation tool on Earth for the past 800 years, is it still useful as we venture further into space? According to scientists, the answer is not straightforward.
On Earth, the compass points north thanks to the planet’s magnetic field. Earth generates this magnetic field through a mechanism called geodynamo, created by electric currents flowing in its molten metal core. The Earth’s magnetic field extends about 37,000 km towards the Sun and at least 370,000 km on the opposite side. The region of space governed by this magnetic field is known as the magnetosphere.
In space, the compass will point towards the north pole of the strongest magnetic field in the area.
Where will a compass point in space?
In space, the compass still functions, but it does not necessarily point to Earth. Instead, it will direct towards the north pole of the strongest magnetic field in the vicinity. If an astronaut uses a compass within the Earth’s magnetosphere, it can continue to detect the planet’s magnetic field and point in the right direction. However, outside the magnetosphere, other factors will influence the compass’s direction.
For example, the magnetosphere of Jupiter is the largest in the Solar System, spanning up to 21 million km, and can deflect your compass. This magnetic field is generated by the planet’s metallic hydrogen core and is currently being studied by the Juno spacecraft.
As we delve deeper into interplanetary space, the compass will be affected by the heliosphere – the magnetic field of the Sun. The heliosphere extends three times the distance from the Sun to Pluto and carries a weak magnetic field generated by solar winds. However, the Sun’s magnetic field is very complex, constantly changing, and even reverses polarity according to the star’s activity cycle, making the use of a compass impractical.
Some planets, like Mars and the Moon, once had strong magnetic fields due to geodynamo, but these have diminished as their cores cooled. Nevertheless, their crusts still retain traces of ancient magnetic fields, known as crustal magnetism. An astronaut on Mars or the Moon may detect this magnetic field, but it is too weak for accurate navigation.
Although not useful for navigation in space, the compass still holds scientific value. Highly sensitive magnetic field measuring devices, known as magnetometers, are used by NASA to study plasma interactions and signs of ancient magnetic fields on planets.
As Jared Espley, a scientist at NASA’s Goddard Space Flight Center, remarks: “Measuring magnetic fields is key to understanding what is happening inside a planet“.
