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Why the moon’s early magnetic field may be responsible for life on earth



The habitability of the planet depends on many factors. One is the existence of a strong and long-lasting magnetic field. These fields are generated thousands of kilometers below the planet’s surface in its liquid core and extend far into space – protecting the atmosphere from harmful solar radiation.

Without a strong magnetic field, a planet struggles to hang on to a breathable atmosphere – which is bad news for life as we know it. A new study published in Science Advances suggests that the Moon’s now extinct magnetic field may have helped protect our planet̵

7;s atmosphere when life formed about 4 billion years ago.

Today, the Earth has a strong global magnetic field that protects the atmosphere and satellites with low orbits from harsh solar radiation. In contrast, the moon has neither a breathable atmosphere nor a global magnetic field.

Global magnetic fields are generated by the motion of molten iron in the nuclei of planets and moons. Keeping the fluid moving requires energy, such as heat trapped inside the core. When there is not enough energy, the field dies.

Without a global magnetic field, the charged particles from the solar wind (radiation from the sun) close to a planet generate electric fields that can accelerate charged atoms, known as ions, out of the atmosphere. This process takes place today on Mars, and it loses oxygen as a result – something that has been measured directly by the Martian atmosphere and the volatile evolution (Maven) mission. The solar wind can also collide with the atmosphere and knock molecules out into space.

The Maven team estimates that the amount of oxygen lost from the Martian atmosphere throughout its history is similar to that contained in a global water layer, 23 meters thick.

[Read: The Moon’s surface is rusting — and Earth may be to blame]

Probes old magnetic fields

The new research examines how the early fields of the Earth and the Moon may have interacted. But it is not easy to examine these old fields. Researchers rely on ancient rocks containing small grains that were magnetized as the rocks formed, saving the direction and strength of the magnetic field at that time and place. Such rocks are rare, and the extraction of their magnetic signal requires careful and delicate laboratory measurement.

An image of the old moon with magnetic field lines.