Extra Planets requires Galacticraft craft minimum build #401. You currently have #375. You need to update Galacticraft, and by extension, Micdoodlecore and galacticraft planets.
If you look in the log, it says
Caused by: java.lang.NoClassDefFoundError: micdoodle8/mods/galacticraft/api/item/IItemThermal
That means it's looking for a class but can't find it. This usually means something with versions. Perhaps wrong version of Minecraft. Perhaps a mod is built for a certain version of a mod. In this case, Extra Planets requires Galacticraft #401 at least, probably because #401 added something to the API which Extra Planets uses. Thus you need to update Galacticraft.
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