# Would the magnetic fields of double-planets clash? and what would happen then?

I will take the basic properties of a previous post

"To make it easier, assume both planets have same mass, radius, and atmosphere as Earth, they orbit each other at a very close distance of 30,000km and they are tidally-locked, in that case the other planet will look very big.

They are orbiting a Sun-like star, in the habitable zone."

Assume they are beyond the Roche limit (change the distance if necessary) and assume both have magnetic fields, would both magnetic fields clash/overlap? if so, would it be dangerous for people? or just fancy auroras.

• Planetary magnetic fields, as large and impressive as they are, are actually fairly weak. That massive power is spread out over an equally massive volume. So the basic answer is, "not much if anything." Assuming the poles of the two planets were identical, the magnetic fields would simply merge and wobble a bit, but otherwise provide additional protection for the planets. What might be interesting (and beyond my knowledge to answer) is if there would be a difference should the two planets have opposing poles.
– JBH
Commented Mar 4, 2023 at 22:55

With a simplified explanation, the magnetic fields of the two planets would find a configuration of equilibrium, more or less how it happens with the magnetic fields of the Sun and Earth.

The picture below shows the situation for our planet

Mind that it is not exactly the same as what you describe, since Sun and Earth are not exactly comparable. However, also with the two planets, the magnetic fields would arrange in a situation of equilibrium, depending on the distance from the two sources.

There would be danger only in volumes where the accelerated particles would emit radiations, like it happens in the Van Allen belt for Earth.

• Will auroras be 24/7 or normal like earth? Cuz I remember (if my knowledgeis is right) that ganymede have auroras that are caused by Jupiter's field Commented Mar 4, 2023 at 20:36
• Auroras pretty much are 24/7 on Earth. Commented Mar 5, 2023 at 18:03

As it happens, in our solar system the two closest worlds with reasonably strong magnetic fields are Jupiter and its moon Ganymede.

And the interaction between their two magnetic fields has a lot of interest to those interested in magnetism.

https://en.wikipedia.org/wiki/Ganymede_(moon)#Magnetosphere

And I can imagine that in some situations the interaction between the two magnetic fields could suggest plots of science fiction stories.

For example, a vehicle using magnetic interactions to travel in space - which would probably be very slow to accelerate or decelerate or change course, but might save on fuel for a satellite needing to keep in position, for example.

Some macroscopic lifeforms have been levitated by magnetism. I doubt if your world could have magnetic fields strong enough for that. But possibly interactions between the magnetic fields of the two planets might be strong enough to levitate and move microscopic organisms important to the plot.

I strongly believe that most Earth like planets will not have magnetic fields strong enough for the interaction between the magnetic fields of two twin planets to be important. But a sufficiently clever writer might be able to give the planets magnetic fields as strong as possible without being lethal to life, and then find a a way to have some effects of their interaction important to the plot.

For organisms living there nothing much would happen, as those fields are really really weak. Just think about it, even a small magnet can influence a compass, as it produce stronger field (at that distance). Depending on how static the clash between fields is your animals (those that evolved on those planets) either won't use magnetism for navigation at all, or they would use it more than on Earth.

But the biggest consequence of your system is that you would most likely get some pretty sweet auroras!