In general, the inferred equivalent internal dipole field is smaller when estimated on the basis of magnetospheric size and shape (~150–200 nT R3).[26] Recent Earth-based radar measurements of Mercury's rotation revealed a slight rocking motion explaining that Mercury's core is at least partially molten, implying that iron "snow" helps maintain the magnetic field.[27] The MESSENGER spacecraft was expected to make more than 500 million measurements of Mercury's magnetic field using its sensitive magnetometer.[3] During its first 88 days in orbit around Mercury, MESSENGER made six different sets of magnetic field measurements as it passed through Mercury's magnetopause.[28]