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Comparative Planetology Overview The Earth as a Template Understanding The Outer Planets Jupiter, The the governing parameters Saturn, Neptune & Uranus Terrestrial Planets Mercury, EAS 4360/6360 Venus, Mars 35:1 What is Comparative Planetology? to Understanding the Governing Parameters: The known unknowns: Atmosphere, Ionosphere, Magnetosphere, Composition, Solar Radiation Flux, Solar Wind Are there unknown unknowns? … EAS 4360/6360 35:2 Comparative Planetology The Earth as a Template: EAS 4360/6360 35:3 Comparative Planetology: Earth Template Parameter Space: Size Magnetic Field (dipolar) Solar Wind (variable) Ionosphere (conductivity) ~ 6378 km ~ 31,000 nT ~ 450 km/s , 8 cm-3, 6 nT Variable: latitude, direction, and day/night Dynamics: Sub-storms and Geomagnetic Storms -Generally governed by the Solar Wind and perturbations in upstream conditions (consider dynamic pressure changes and magnetic field orientation/strength, Mach number of the flow) EAS 4360/6360 35:4 Comparative Planetology Magnetospheres of the Outer Planets (MOP): MOP: - can learn about them by comparing with Earth (which we know a lot better) - can learn even more about the universe in general because there are very important differences between Earth and MOP. EAS 4360/6360 35:5 Comparative Planetology MOP -- Overview Intrinsic Magnetic Field Strengths Vary Planet Earth Jupiter Saturn Uranus Neptune Distance (AU) 1.0 5.2 9.5 19.2 30.1 EAS 4360/6360 Mag Mom (ME) 1 20,000 580 49 27 Radius / RE 1.0 11.0 9.5 4.2 3.9 surface B (T) 3.1E-05 0.00043 2.1E-05 2.1E-05 1.4E-05 magnetopause L 11 45 21 27 26 35:6 Jupiter Knowns: R ~ 71,500 km B ~ 430,000 nT SW ~ 1 nT, ~ 0.2 cm-3 ~ 400 km/s Unknowns: Plasma sources Moons Rotation Rate? EAS 4360/6360 35:7 Jupiter Jupiter -- Momentum Coupling As plasma from Io flows outwards its rotation decreases (conservation of angular momentum) Sub-corotating plasma pulls back the magnetic field Curl B -> radial current J x B force enforces rotation Khurana 2001 Field-aligned currents couple magnetosphere to Jupiter’s rotation Cowley & Bunce 2001 EAS 4360/6360 35:8 Jupiter Aurora Oval Rotates with Jupiter, and there’s more… Jupiter’s Aurora - The Movie Fixed magnetic co-ordinates rotating with Jupiter Clarke et al. Grodent et al. HST EAS 4360/6360 35:9 Jupiter Aurora The main auroral oval is the signature of Jupiter’s attempt to spin up its magnetosphere -- magnetically maps to the region where corotation breaks down. Clarke et al. EAS 4360/6360 35:10 Jupiter Aurora Footprints The aurora ‘footprints’ magnetically map to the orbital location of three Galilean moons: Io, Europa, and Ganymede -- they track around around the oval with the orbital speed of the moons relative to rotation. EAS 4360/6360 35:11 Jupiter Aurora Footprints This was quite useful for constraining magnetic mapping and the radial location of corotation breakdown. EAS 4360/6360 35:12 Jupiter Moons - Internal Plasma Source Io EAS 4360/6360 35:13 Jupiter Moons - Internal Plasma Source Pilan Plume Io’s Active Volcanoes Prometheus Pilan 5 months apart Pele InfraRed Tvashtar erupts during New Horizons Flyby Jupiter Moons - Internal Plasma Source After Spencer & Schneider 1996 EAS 4360/6360 35:15 Io Plasma Torus Warm Torus: 90% of plasma Ne~2000 cm-3 O+ S++ Ti~100eV Te~5eV UV power ~ 2 x 1012 W Cold Torus: Ne~1000 cm-3 S+ Ti~Te~1 eV EAS 4360/6360 Source: Extended clouds O, S, SO, SO2, S2..? ~1 ton/s ~3 x 1028 ions/ s Dn/n~2% per rotation Local Io Source? ~20%? 35:16 Io Plasma Torus Cassini UVIS - PI Larry Esposito, University of Colorado • Movie - 45 days as Cassini approached Jupiter • Integration over multiple lines in the EUV E EAS 4360/6360 = direction of dipole tilt W 35:17 Io Plasma Torus Io spews out volcanic material (1000 kg/ s), which ionizes (S+, S++, O+, SO2+) Observing the Io plasma torus from Earth using highly visible spectral lines like sodium. Sodium Sodium EAS 4360/6360 35:18 Io Plasma Torus EAS 4360/6360 35:19 Io Plasma Torus Radial Distance Results in Interchange Instability - Spreading of the Torus EAS 4360/6360 35:20 Connerney et al. The Io Aurora Clarke et al. Infrared Io Ultraviolet - energetic particles bombard atmosphere - ‘wake’ emission extends halfway around Jupiter EAS 4360/6360 35:21 The Io Aurora Downward Current Upward Current Stag EAS 4360/6360 nan t flow 35:22 Ganymede: A Magnetosphere within a Magnetosphere Torrence Johnson EAS 4360/6360 35:23 Ganymede’s Magnetosphere Radius = 2634 km B = 720 nT Jovian ‘Wind’ ~ 174 nT ~ 184 km/s ~ 3-6 cm-3 Heavy mass ions (O+) EAS 4360/6360 35:24 Ganymede’s Magnetosphere & Aurora HST observations of oxygen emissions - McGrath Aurora on Ganymede Trailing Side = Upstream North Polar Cap Leading Side = Downstream South Polar Cap Khurana & Pappalardo Jupiter -- Magnetospheric Dynamics Equatorial View Polar View Dawn Dawn Dusk Dusk Side View EAS 4360/6360 35:26 Jupiter -- Magnetospheric Dynamics Equatorial View Dawn Polar View Dawn Dusk Hill Region Subcorotating plasmasheet Dusk Main Auroral Oval Side View EAS 4360/6360 35:27 Jupiter -- Magnetospheric Dynamics Equatorial View Dawn Dusk Polar View Dawn Inward motion -> less load on Dusk ionosphere Outward motion -> more load on ionosphere Outer Magnetosphere “Cushion Region” Side View EAS 4360/6360 35:28 Jupiter -- Magnetospheric Dynamics ? ? ? Equatorial View Dusk Dawn Polar View Dawn How important is the Dungey Cycle? Dusk ? ? ? How Much of Polar Flux is Open? Side View EAS 4360/6360 35:29 Relating Auroral Regions to Dynamics Dusk Dawn Tail Reconnection? Less load = weaker currents Cusp? More load = stronger currents, filaments Dayside Reconnection? EAS 4360/6360 35:30 Jovian Dynamics -- Some Outstanding Questions • How is angular momentum transferred from Jupiter to the magnetosphere? Slippage in ionosphere vs. potential regions? • What happens in the magnetotail? • Are plasma losses via ~steady, small-scale crossfield “drizzle” or occasional, large, plasmoid events? • What triggers disruptions? • What are the roles of Io’s volcanism vs. solar wind in magnetospheric variability? Other moons? • Can we decipher the clues from the aurora? EAS 4360/6360 35:31 Upcoming Mission to Jupiter: Juno Juno flies through the polar regions • traverses field lines that couple to all regions of the magnetosphere • acceleration region of auroral particles • source regions of radio emissions • crosses Io wake (and fluxtube, with luck) EAS 4360/6360 35:28 Saturn Knowns: Unknowns: R ~ 60,300 km Neutral / Plasma sources B ~ 21,000 nT Moons SW ~ 1 nT, < 0.1 cm-3, ~ 400 km/s Rings EAS 4360/6360 35:33 Saturn - Role of Enceladus The Geysers of Enceladus In 2006, it was discovered that Enceladus had geysers of water spewing from its surface. This is the probable mass source for the (mostly water ion) E-Ring plasma torus. EAS 4360/6360 35:34 Saturn - Role of Enceladus Enceladus’ plume is the probable mass source for the (mostly water ion) plasma torus, as well as the neutrals and ice/dust that make up the E-ring, extending from 3-9 Saturn radii. EAS 4360/6360 35:35 Saturn - Role of Enceladus Electron flux (upper panel) and ion flux (lower) from Enceladus flyby electron E3: March 12, 2006 Wake e- depleted Stagnant ions ion Dust impacts Plume EAS 4360/6360 35:36 Saturn - Role of the Rings Saturn’s Rings Saturn’s rings are labeled by letters A, B, C, etc. Energetic (plasma) particles are absorbed by the rings, not in the gap. EAS 4360/6360 Energy in eV Cassini Division Cassini Division 35:37 Saturn - Plasma Radial Transport Saturn’s Plasmasphere The rotationally dominated Saturnian magnetosphere has a much larger “plasmasphere” than Earth. It is the E-Ring cold torus, mostly water group ions, which extends out to 9 Saturn radii. -- Outside the E-ring torus, Saturn’s magnetosphere contains warmer, less dense plasma, more like Earth’s plasma sheet. Saturn Injections Warmer plasma gets injected into the cold plasma torus by an unknown mechanism. EAS 4360/6360 Perhaps an interchange instability? 35:38 Saturn Aurora Saturn Aurora are still not completely understood. The auroral forms are often“spiral” shaped, and the brightening seems to happen on the dayside… EAS 4360/6360 35:39 6 Average Zones X Simultaneous Cassini SW Observations Jan 2004 Low field rarefaction region Minor compression event Intermediate field strength rarefaction region Major compression region Saturn Aurora - Substorm-like or Something Else? Saturn Aurora - Substorm-like or Something Else? EAS 4360/6360 35:43 Earth - Jupiter - Saturn Earth’s magnetospheric dynamics are driven by variations in the solar wind, which generate substorms and geomagnetic storms reflected in perturbations to the magnetic field morphology as well as in the aurora. Jupiter’s magnetosphere appears to be rotationally driven, due to both the rapid rotation of the planet and the internal plasma loading provided by Io. The aurora is only somewhat impacted by solar wind changes. Magnetospheric interactions with the Galilean moons is also reflected by the auroral footprints. Saturn’s magnetosphere rotates rapidly, and contains both sources and sinks of plasma from Enceladus and the rings. The aurora appears to be dependent on solar wind variations, but responds quite differently than what we observe at the Earth. EAS 4360/6360 35:44 Giant Planet Magnetospheres Uranus & Neptune - - - - Highly asymmetric, Highly non-dipolar Complex transport (SW + rotation) Multiple plasma sources (ionosphere + solar wind + satellites) EAS 4360/6360 35:45 Non-magnetized Objects How do Venus, Mars, and Titan interact with a magnetized plasma? No intrinsic magnetic field Atmosphere/Ionosphere (Venus > Titan > Mars) Similar magnetized ‘wind’ conditions EAS 4360/6360 35:46 Venus Radius ~ 6051km Gravity ~ 8.9 m/s2 EAS 4360/6360 Without a global magnetic field, the solar wind interacts directly with Venus’ upper atmosphere, specifically the ionosphere. Ions outside the ionopause become trapped on the solar wind magnetic field and carried away, ‘pickup ions.’ 0.72 AU from Sun Atm -> 92 bars, <T> ~ 737 K (464 C) 35:47 Venus EAS 4360/6360 35:48 Mars While Mars does not have a global magnetosphere, localized crustal magnetism can create ‘mini magnetospheres’ Ions outside the ionopause or minimagnetopause become pickup ions. Radius ~ 3396 km Gravity ~ 3.7 m/s2 EAS 4360/6360 1.5 AU from Sun Atm -> 6.36 mb, <T> ~ 213 K (-60 C) 35:49 Mars D. Brain EAS 4360/6360 Due to the magnetic anomalies, Mars has a partial magnetopause. The edges appear to be correlated with observations of solar wind particles precipitation, or aurora! Much too diffuse to observe with HST. 35:50 Titan Mostly interacts with the magnetized plasma of Saturn’s magnetosphere, very close to Saturn’s dayside magnetouause. Occasionally lies in the magnetosheath or even in the solar wind! Radius ~ 2575 km EAS 4360/6360 20 Rs from Saturn 35:51 Where is Titan? EAS 4360/6360 35:52 Titan’s Near-Space Environment Snowden et al. 2007 Draping of Saturn’s magnetic field due to interaction with Titan’s ionosphere/atmosphere. Rotational flow is Subsonic but Super Alfvénic. EAS 4360/6360 35:53 Titan - Saturn - Solar Wind Coupling Winglee et al., 2009 EAS 4360/6360 35:54 Mercury -- The Closest Magnetosphere to the Sun A relatively small magnetosphere, close to the Sun. Very susceptible to solar wind conditions and changes. Very diffuse and unique atmosphere… much to learn from Messenger! Radius ~ 2440 km EAS 4360/6360 Magnetic Field ~ 340 nT 35:55 Mercury’s Magnetosphere No atmosphere thus no ionosphere but exosphere No plasmasphere Weak magnetic field Multi-ion plasma Small magnetosphere EAS 4360/6360 35:56 Messenger: Mission to Mercury Why go to Mercury? Science Questions Driving the Mission and Instrumentation -Q.1. Why is Mercury so dense? Q.2. What is the geologic history of Mercury? Q.3. What is the nature of Mercury's magnetic field? Q.4. What is the structure of Mercury's core? Q.5. What are the unusual materials at Mercury's poles? Q.6. What volatiles are important at Mercury? ‘Mercury: The Key to Terrestrial Planet Evolution’ EAS 4360/6360 35:57 Messenger: Mission to Mercury http://messenger.jhuapl.edu/instruments/index.html EAS 4360/6360 35:58 Mercury Messenger Radius ~ 2575 km EAS 4360/6360 20 Rs from Saturn 35:59 Evidence for Subsurface Oceans Image credits: Planetary Photo Journal Jovian System Io (5.9 RJ) Europa (9.5 RJ) Ganymede (15.1 RJ) Callisto (26.6 RJ) Clarke, 2002 Image Credit: John Spencer The wobble of Jupiter’s magnetic equator over the orbital path of the Galilean moons causes a periodic dB/dt local to the moons. Induced vs. Intrinsic Magnetic Fields Galileo: E4 Galileo: E14 Kivelson et. al., 2000 Galileo: E26 Astrobiology Implications