11 March 2004
Uranus and Neptune: The odd couple
The Voyager 2 mission to Uranus in 1986 and Neptune in 1989 mapped the magnetic fields of both planets, with unexpected results. The magnetic fields of Earth, Saturn, and Jupiter have two poles that align roughly with the planets' rotational axes, but the fields of Uranus and Neptune have multiple poles that tilt with respect to the orbital axis. Various mechanisms have been suggested to explain these peculiar fields but no consensus has been reached. A new numerical simulation of the fluid dynamo generating the magnetic fields suggests that the field morphology may be a direct result of the planets' interior structures. A thin outer shell surrounding a large solid inner core, with low electrical conductivity, would produce a dynamo capable of generating the observed fields. No new missions to Uranus and Neptune are scheduled, but parts of this new model could be tested using data from Messenger and Cassini, due to visit Mercury and Saturn in the near future.
Convective-region geometry as the cause of Uranus'
and Neptune's unusual magnetic fields
SABINE STANLEY & JEREMY BLOXHAM
Nature 428, 151–153 (2004); doi:10.1038/nature02376
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Planetary science: Secrets of the deep
JONATHAN AURNOU
The magnetic fields of Uranus and Neptune are markedly different from
those of other planets in the Solar System. Can this be attributed to
structural differences deep inside the planets?
Nature 428, 134–135 (2004); doi:10.1038/428134a
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