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An interesting idea that popped up in my previous question on the feasibility of large scale life on a gas giant was a form of energy production similar to photosynthesis, instead absorbing the EM energy from a gas giant's magnetic field to break down chemicals in the methane, ammonia, oxygen and other necessary gasses.

How would these organisms absorb the EM energy and make it useful? As an added question, would multicellular magnetosynthetic 'plants' be able to survive using magnetosynthesis?

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"EM energy" is light. I.e., photosynthesis. You might be able to get useful energy from the radio noise generated by charged particles captured in the plane's magnetosphere, but your plants would have to be pretty big to develop biological radio rectennae. And they would need very highly developed ion-pumping mechanisms to capture and save up teensy bits of energy from each radio photon in order to add it all together to power any single useful reaction.

You cannot extract energy from a magnetic field without destroying that magnetic field. If you want to generate energy using the planet's magnetic field, the only way to do that is for the organisms in question to move very quickly across the magnetic field lines, and then harvest their kinetic energy via magnetic induction. In order to get biologically-useful voltages out of that, your magnetosynthetic plants would have to be very large, even more so than radio-eating plants, and therefore most likely multicellular. It is perhaps possible that such plants could live in cyclones or high-speed circulation bands such that winds push them across the magnetic field lines, and that's where the energy ultimately comes from, but it seems to me that this would be a rather marginal energy-extraction strategy; you'd do better relying on static electricity in storm clouds, or thermal gradients between different layers of the atmosphere.

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  • $\begingroup$ Your last part on living in cyclones and storm areas is exactly what I'm aiming for! Immense magentosynthetic plants that swirl between the magnetic field lines, absorbing energy and also taking from the static electricity within the storm clouds. $\endgroup$ – Jefferey Dawson Jul 22 at 22:02
  • $\begingroup$ Just a sidenote, just how big would these plants have to be? $\endgroup$ – Jefferey Dawson Jul 23 at 1:51
  • $\begingroup$ @JeffereyDawson The necessary size for magnetovores depends on the specifics of field strength and windspeed. The sizes for radiosynthetic organisms are much easier to figure out--a rectenna needs to be at least a half wavelength long, and, e.g., Jupiter emits a lot of radiation in decameter ranges, so radiosynthesizers would need to be between 10 and 100 meters long. As a first approximation, add an order of magnitude for magnetovores--so, in the realm of a kilometer. $\endgroup$ – Logan R. Kearsley Jul 23 at 14:44

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