Tilts and Obliquities!

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Arabella Willis
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1 Fran Bagenal! University of Colorado! Tilts and Obliquities! Offset Tilted Dipole Approximation

Earth Stanley & Bloxham 2006 Jupiter Saturn B radial @ surface Uranus Neptune Magnetic

2 Earth Stanley & Bloxham 2006 Jupiter Saturn B surface Uranus Neptune Magnetic Potential 3-D harmonics V coefficients - constants functions n= m=

3 Same technique used to model cosmic microwave background or interior of Sun with Helioseismology Earth - International Geomagnetic Reference Field Complexity... 4 pages later... g h Time

4 Declination in degrees International Geomagnetic Reference Field 2010 Total Intensity in nt Inclination in degrees Br surface 1. From accurate measurement of surface field: 2. Extrapolate to core-mantle boundary = dynamo 3. Derive core flows 20 km/yr 4. Secular variation & reversals... h=horizontal r=radial Br core-mantle boundary Hulot et al. 2010

5 Geomagnetic = best fit dipole Magnetic = where B = Br What's the difference between Magnetic and Geomagnetic Poles?

6 Br through a reversal Hulot et al Pavlov & Gallet 2005 Polarity reversals: 1. variable in duration and 2. rate

7 Moon & Mars: All Crustal Remanent Magnetization Moon Core field Crustal field Mars Earth Mars Moon Did Moon ever have dynamo? Mars' dynamo died >3.5 BYA. Mars

Rock Io Iron R c /R p =0.55 Mercury Venus Earth Moon Mars Ganymede Planet Dynamo R c /R p B o [nt] Mercury Yes (?) 0.75 195 Venus No 0.

8 Stanley & Glatzmeier 2010; Christensen 2010 Planetary Dynamos Volume of electrically conducting fluid 1! which is convecting and rotating 2! All planetary objects probably have enough rotation - the presence (or not) of a global magnetic field tells us about 1! and 2! Rock Io Iron R c /R p =0.55 Mercury Venus Earth Moon Mars Ganymede Planet Dynamo R c /R p B o [nt] Mercury Yes (?) Venus No 0.55 Earth Yes ,000 Moon No 0.2? Mars No, but in past 0.5 Ganymede Yes 0.3? 720 What drives dynamos in tiny Mercury & Ganymede? Why don't Venus or Mars have dynamos?

..Mantle convection controls heat flow from core. Then.

9 Hot surface - small Tgradient Small cooled off Why Don't Venus or Mars have Dynamos? Enough rotation even for Venus Stevensen 2010 Conducting fluid core probably Lack of convection in core? 1. If...Mantle convection controls heat flow from core. Then...Lack of plate tectonics suggests less efficient cooling of interior and lower heat flux from core 2. No inner core means no latent heat of solidification and no enhancement of lighter material in the outer core

10 Mercury & Ganymede! What drives convection in these small bodies?! Iron! Core! -Liquid?! Liquid! The test of a good Fe + S! theorist Core! is the ability to explain any outcome, even when the data are wrong!!- David Stevenson! Liquid! Iron! Core! Jupiter Saturn Molecular state ~2.5 Mbar phase transition Rc/Rp=0.84 Rc/Rp=0.6 Plasma state Saturn has lower mass! lower pressures! smaller region of metallic hydrogen! weaker magnetic field

11 Uranus Neptune Rc/Rp=0.7 Rc/Rp=0.8 Uranus and Neptune have much less mass! Lower pressures! No metallic hydrogen! Weak & irregular magnetic fields produced in water layer, deep below gas envelope Planet Rc/Rp Bo [µt] Tilt Quad/ Dipole Earth Jupiter Saturn < Uranus Neptune Dipolar Irregular Jupiter Earth B surface Saturn Uranus Neptune Stanley & Bloxham 2006

12 Neptune Uranus Jupiter Earth Saturn Stanley & Bloxham 2006 Modeling Uranus' & Neptune's nondipolar fields with a thin-shell dynamo over a stratified core Even with the Best Equation of State Still lots of unknowns Jupiter Juno Launched Aug. 5 th Arrives Jul Guillot et al. 2004

Juno Magnetic Spectra of Earth and Jupiter Current

shape, dynamo radius, and secular variations Now

13 Juno Magnetic Spectra of Earth and Jupiter Current knowledge of Jupiter is limited to n < 4 Earth dynamo at n >14 is hidden by crustal field Juno will measure out to n ~ 20 Determine spectral shape, dynamo radius, and secular variations Now we have magnetic fields... what about magnetospheres? Jupiter

R Chapman-Ferraro /R p ~ {B o 2 /2 µ o ρ sw V 2 sw }1/6 Mercury Earth Jupiter Saturn Uranus Neptune B o Gauss.003.31 4.28.22.

14 R Chapman-Ferraro /R p ~ {B o 2 /2 µ o ρ sw V 2 sw }1/6 Mercury Earth Jupiter Saturn Uranus Neptune B o Gauss R CF Calc. R M Obs. 1.4 R M 10 R E 42 R J 19 R S 25 R U 24 R N R U R M R E R J R S R N

15 Mercury & Ganymede Mercury - Magnetic field detected by Mariner 10 in 1974! Ganymede - Magnetic field detected by Galileo in 1996! Solar! Wind! B surface ~ 1/100 Earth! Diameter of Earth!

16 Ganymede Uranus - Highly asymmetric, - Highly non-dipolar - Complex transport (SW + rotation) - Multiple plasma sources (ionosphere + solar wind + satellites) Toth et al.

17 Neptune Similarly complex as Uranus Zieger et al.

18 Juno arrives at Jupiter July 4th 2016 Juno Microwave Radiometer (JPL) Magnetometer (GSFC/JPL) Energetic Particle Detector (APL) Plasma (SwRI) Waves (Iowa) UV Spectrometer (SwRI) IR Spectal Imager (Rome) Visible Camera (Malin) Launch 2011 Arrive 2016

Dynamics Polar Magnetosphere Juno Probing

19 Juno Juno Mission Design Launch: August year cruise Baseline mission: 32 polar orbits Perijove ~5000 km 11 day period Spinner Solar-powered Science Objectives: Origin of Jupiter Interior Structure Atmosphere Composition & Dynamics Polar Magnetosphere Juno Probing Jupiter's Deep Interior Microwaves tell us about the outer weather layers - the amount of water Magnetic and Gravity Fields tell us about the deep interior

20 Juno Polar Magnetosphere Juno passes directly through auroral field lines Measures particles precipitating into atmosphere creating aurora Plasma/radio waves reveal processes responsible for particle acceleration UV & IR images provides context for in-situ observations

Juno. Fran Bagenal University of Colorado

Juno. Fran Bagenal University of Colorado Juno Fran Bagenal University of Colorado Cassini 2000 Cassini 2000 Jupiter s Pole When the Galileo Probe entered Jupiter clouds Expected ammonia + water clouds But found! very few clouds Probe entered