The earth and the moon once shared a magnetic field

Moon protection screen: The moon’s magnetic field once protected the young earth from the violent eruptions of the young sun. Because according to a new model, the magnetic fields of the earth and the moon were connected to each other until about 3.5 billion years ago. This connection could have made a decisive contribution to protecting the earth from the loss of its atmosphere, researchers report in the journal “Science Advances”.

The magnetic field of our planet is the most important Protective screen. It protects the earth from cosmic rays and the energy-rich particle streams from solar storms. The driving force behind this invisible magnetic screen is the electromagnetic interaction between liquid and solid iron in the core of the earth – the geodynamo. On the other hand, there could be the young earth that is still fully glowing inside Convection current generated the magnetic field in the core.

In its early days, the moon had a bipolar magnetic field similar to that of the earth. © NASA

What about the moon

But how is our neighbor, the moon? Today the interior is too cold and too solid to create a magnetic field. Therefore, the lunar surface is largely unprotected from cosmic rays. But what did the solar system look like in the beginning, when the moon was still warm? catastrophic emergence behave yourself? Planetary researchers believed for a long time that the iron core of the moon was too small to function as a magnetic dynamo.

Analyzes of lunar rocks from the Apollo missions have refuted this: They show that the earth satellite had a magnetic field shortly after its formation. “4.2 to 3.4 billion years ago, the moon’s magnetic field was at least as strong, if not stronger, than the Earth’s magnetic field today, given the strength on the surface.” explains James Green from NASA. But that means that because the moon was much closer then than it is today, the magnetic field could also have influenced our planet.

Coupled magnetic fields

Green and his team examined whether this is the case using geophysical model simulations. To do this, they reconstructed the positions and magnetic fields of the earth and moon about four billion years ago. At that time, the two celestial objects were only about 18 earth rays apart – today there are 60. The researchers investigated whether and how the magnetic fields of the moon and earth interact in different orbital positions.

The surprising result: up until about 3.5 billion years ago, the magnetic fields of the earth and moon were connected to one another. In the middle and higher latitudes in particular, there were connections between the field lines that generated an overlapping magnetic field. “Our results suggest that this era of coupled magnetospheres lasted hundreds of millions of years,” report Green and his team.

Double protection against the young sun

This pairing could have been a key benefit for Young Earth. Because the magnetic field of the moon offered additional protection against the violent eruptions of the still young sun. “The moon provided Earth with a significant protective barrier from the solar wind and could have played a crucial role in helping young Earth maintain its atmosphere at this point,” explains Green. Without the atmosphere, life on earth would probably never have developed.

Specifically, the coupled magnetic fields had a double protective effect: They reduced the size of the zones in the area of ​​the earth’s poles in which the solar wind can penetrate the magnetic grid. If the moon was on the sunny side of the earth, it also protected it almost completely from the solar wind. “The moon’s magnetosphere received the full power of the solar wind and provided an effective protective shield for the earth’s atmosphere – even during strong solar eruptions,” the researchers write.

Future lunar astronauts could provide the proof

This shared magnetic past of Earth and Moon did not end until the moon cooled and the magnetic field became weaker and weaker. According to calculations by Green and his team, about 3.2 billion years ago the moon field was so weakened that it was no longer connected. At the same time the moon drifted further and further outwards and thus out of reach. 1.5 billion ago the satellite lost the last remnants of the magnetic field.

The exciting thing: In just a few years, lunar astronauts could be looking for evidence of this scenario on the moon – and possibly find it. Because under the US. Mission Artemis Ice and rock samples must be collected at the south pole of the moon. If there were really coupled magnetic fields, traces of gases could be found in these samples, which at this point in time are propagating along the coupled field lines from the earth to the moon.

“Samples from the moon’s permanently shaded polar regions could make a crucial contribution to verifying the assumption of our model,” says Green. (Science Advances, 2020; doi: 10.1126 / sciadv.abc0865)


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