Do all planets have a magnetic field?

Most planets do. Of the main planets in our Solar System, only Venus and Mars lack global magnetic fields. Mars has crustal magnetic fields in its ancient southern hemisphere. This is evidence for an early global Martian magnetic field, which stopped 3.8 billion years ago, a time when life may have developed – we hope to find out with the Rosalind Franklin rover in 2023. The solar wind has stripped the Mars atmosphere; now it has only one per cent of Earth’s atmospheric pressure. The planetary magnetic fields are all different. Earth’s north magnetic pole is currently in the Southern Hemisphere, and it’s due to ‘flip’ in the next few thousand years. We don’t understand why Mercury has a magnetic field at all – BepiColombo will find out in 2025. If you could see Jupiter’s magnetic field, it would be many times the size of the Moon; Saturn’s field is not as large. Uranus and Neptune’s fields are at large angles from their rotation axes. Ganymede has a unique magnetic field – a magnetosphere within Jupiter’s huge magnetosphere – and this will be visited by the ESA’s JUICE mission in the 2030s.