Magnetic field of Mercury confirmed

ON March 16, 1975 the US spacecraft Mariner 10 underwent its third and final encounter with Mercury. This unique and for tuitous event occurred because the heliocentric orbital period of Mariner 10 was 176 d exactly twice that of the orbital period of Mercury. The principal objective of the third fly-by was to confirm or reject the suggestion from the first fly-by on March 29, 1974 that Mercury may possess a modest intrinsic magnetic field sufficient to deflect the solar wind flow 1–2 . The quantitative analysis 3 of the Mercury I data yielded an estimate of the planetary magnetic dipole moment equal to 5.1 × 10 22 gauss cm 3 and oriented 7° from the orbit normal. The spacecraft had not been functioning properly since Mercury I because of various technical failures but the spacecraft engineering team at the NASA Jet Propulsion Laboratory (JPL) managed to achieve the desired objective at Mercury III of a very close dark-side pass. Here we present preliminary results from the NASA Goddard Space Flight Center magnetometer instrumentation on Mariner 10.