On Earth, a compass always points north – but where does it point in space?

On Earth, our planet's magnetic field points north, but in space, things are a bit more complicated.

The compass , humanity's primary navigational tool on Earth for the past 800 years, will it still be useful as we venture further into space? According to scientists, the answer is not simple.

On Earth, a compass points north thanks to the planet's magnetic field. Earth generates this magnetic field through a motor called the geodynamo , which is generated by electric currents flowing through its molten metal core. Earth's magnetic field extends about 37,000km toward the Sun and at least 370,000km away. The region of space dominated by this magnetic field is called the magnetosphere.

In space, the compass will point towards the north pole of the strongest magnetic field in the area.

Where will the compass in space point?

In space, a compass still works, but it doesn't necessarily point toward Earth . Instead, it points toward the north pole of the strongest magnetic field in the area. If an astronaut were to use a compass in Earth's magnetosphere, it could continue to detect the planet's magnetic field and point in the correct direction. Outside the magnetosphere, however, other factors would influence the compass's orientation.

Jupiter's magnetosphere, for example, is the largest in the Solar System, measuring 21 million kilometers across, and has the potential to deflect your compass. This magnetic field is generated by the planet's metallic hydrogen core and is being studied by the Juno spacecraft.

As you venture deeper into interplanetary space, your compass will be affected by the heliosphere – the Sun's magnetosphere . The heliosphere extends three times the distance from the Sun to Pluto and carries the weak magnetic field created by the solar wind. However, the Sun's magnetic field is complex, constantly changing and even flipping polarity over the course of the star's activity cycle, making it impossible to use a compass.

Some planets, such as Mars and the Moon, once had strong magnetic fields due to geodynamo, but they have since faded as their cores cooled. However, their crusts retain traces of their ancient magnetic fields, called crustal magnetofields. An astronaut on Mars or the Moon could detect these magnetic fields, but they would be too weak to accurately orient himself.

Although not useful for navigating in space, compasses still have scientific value. Extremely sensitive magnetic field measuring devices, called magnetometers , are used by NASA to study plasma interactions and ancient magnetic signatures on planets.

As Jared Espley, a scientist at NASA's Goddard Space Flight Center, puts it: " Measuring magnetic fields is key to understanding what's going on inside a planet ."