Cross out the objects below that this rules out from having magnetic fields. Mercury Venus Earth Planet Since the free charges in the molten material must be in motion to generate a magnetic field, only planets with faster rotation rates are likely to have magnetic fields. Refer to Table 7.3, and cross out any planets above that do not have fast rotation rates. TABLE 7.3 Planetary rotation rates and magnetic fields. Mercury Venus Earth Earth's Moon Mars (*-0 means little or none) Rotational Period 59 days 243 days 23.9 hours Earth's Moon 27.3 days 24.6 hours Mars Magnetic Field Strength -0* 0 1 -0* 0 2. Any planet that you have not crossed out above should have a magnetic field. Circle any planet above that you have not crossed out. Does the data in Table 7.3 support your choice(s)? Yes/No (circle one) PART 3 Magnetic Fields The motion of electric charge produces magnetic fields. A magnetic field surrounding a planet is created by free electric charge in the molten, metallic material in the core of a planet set into motion by the planet's rotation. Since a molten core means that a planet has not completely cooled off yet, only planets that are geologically active are likely to have a substantial magnetic field.