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SUMMARY:Planetary Magnetic Fields: Observational Insights and Challenges (
 Keynote speaker) - Jeremy Bloxham (Harvard University)
DTSTART:20220913T080000Z
DTEND:20220913T090000Z
UID:TALK177479@talks.cam.ac.uk
DESCRIPTION:More than a half century of spacecraft observations of planeta
 ry magnetic fields have revealed that no two planets in our Solar System a
 re truly alike magnetically. Mercury has a weak\, relatively axisymmetric 
 field that is displaced along the rotation axis\; Mars had a dynamo that i
 s now extinct\; Venus has no field\; Jupiter&rsquo\;s field is different i
 n the two hemispheres\, with flux concentrated into a few well-defined reg
 ions\; Saturn&rsquo\;s field is highly axisymmetric\; and Uranus and Neptu
 ne have fields that are predominantly non-dipolar\, but different. Earth&r
 squo\;s field is distinctly different from any of these planets. Is this d
 iversity of magnetic field morphology the result of gross interior differe
 nces between the planets or is it simply a result of the sensitivity of dy
 namos to the relevant governing parameters?\nIn the second part of this ta
 lk\, we compare analyzing the Earth&rsquo\;s field with those of the gas g
 iants. For Earth\, it is a reasonable approximation to consider the mantle
  to be electrically insulating so the field may be downwardly continued to
  the core-mantle boundary\, where the radial component of the field is con
 tinuous across the thin boundary layer at the top of the core. Hence\, sur
 face observations can be used to infer the field at the top of the flow fi
 eld in the core. For the giant planets\, the electrical conductivity is a 
 continuous function of depth and so downward continuation is on a less fir
 m footing. Furthermore\, even though magnetic flux is frozen in the deep i
 nteriors of both the Earth and the gas giants\, the Roberts & Scott frozen
 -flux theory of the secular variation\, so useful for Earth\, is not so st
 raightforwardly applied to the case of the case giants. For example\, the 
 gas giants lack a rigid radial boundary at the top of the convective regio
 n so the radial component of the flow does not necessarily vanish. We inve
 stigate these complications using a numerical dynamo model with radially-v
 arying electrical conductivity and a stably stratified region.\nWith Hao C
 ao\, Laura Kulowski\, Rakesh Yadav and the Juno Science Team
LOCATION:Seminar Room 1\, Newton Institute
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