Magnetic field ?
Don't you need an iron core for that ?
Scientists have found that the fundamental mechanism behind the spectacular light shows of auroras on Earth are universal throughout the solar system. Using data from space probe BepiColombo's first flyby of Mercury, the researchers have shown the processes creating auroras on the planet closest to the Sun are shared with …
A magnetic field is generated (in a celestial body) by a dynamo effect. That requires an electrically conductive interior - such as an iron core.
Or, for a more sciency article - https://www.sciencedirect.com/topics/earth-and-planetary-sciences/dynamo-theory
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