the terrestrial planets - summer school alpbach - the... · 2016-07-05 · interior structure...
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Tilman Spohn
German Aerospace Center, Berlin, Germany
The Terrestrial Planets Alpbach Summer School 2014: Geophysics of the Terrestrial Planets
2014-2015 The Rosetta Year
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Mission confirmation Nov. 1993
Launch March 2004
1st Earth gravity assist March 2005
Deep Impact observations Jume/July 2005
Mars gravity assist Febr. 2007
2nd Earth gravity assist Nov. 2007
Steins flyby Sept. 2008
3rd Earth gravity assist Nov. 2009
Lutetia flyby July 2010
Hibernation July 2011- Jan. 2014
Pre landing comet
characterization phase
June – Nov. 2014
Philae landing Nov. 2014
Escort Phase - Dec. 2015
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What is a Terrestrial Planet?
To the atmosphere scientist, a planet with an Earth-like atmosphere. Venus, Mars, and Mercury will
NOT qualify. Titan may!
To the geoscientist, a planet composed mostly of rock and iron. Venus, Mars and Mercury qualify. But
so do other planetary objects such as the Moon, Io, Pluto, and Ganymede. However, these are NOT
planets according to the IAU definition
According to IAU definition passed in 2006, a planet of the Solar System must have three
qualities:
it must be round, indicating its interior is in hydrostatic equilibrium;
it must orbit the Sun;
it must have gravitationally cleared its zone of other debris.
The discovery of Exoplanets has opened new samples of planets and planetary systems, most of the
discovered (presumably) rocky objects being sigifcantly more massive than Earth: Super Eartths and
Mega Earths
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Mercury Venus Earth Mars
Four Planets, four individuals! Many more Moons and „earthlike“ Exoplanets (tbc)
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Exoplanet Summary
Modified from Rauer et al. 2012
Still need more data, in particular mass AND radius
Mercury Venus Earth Mars Moon Ganymede Io
Radius 0.38 0.95 1.0 0.54 0.27 0.41 0.28
Mass 0.055 0.815 1.0 0.107 0.012 0.018 0.015
Density [kg/m3] 5430. 5250. 5515. 3940. 3340. 1940. 3554.
r0 [kg/m3] 5300. 4000. 4100. 3800. 3400. 1800. 3600.
MoI 0.34 ? 0.3355 0.3662 0.3905 0.3105 0.378
Rc/Rp 0.82 0.55 0.546 0.5 0.20 0.3 0.5
Dipole Moment
[1019 A m2]
4.9 <0.4 7980. <2.5 <4x10-9 14 ?
Data, Terrestrial Planets and Moons
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Mercury
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Venus
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Atmosphere
Composition
CO² 96,5%, N² 3,5%
Minor elements H²O, SO2, Ar, CO, He, Ne
Mass: 4.1019 kg
Pressure: 92 atm
av Temperature: 737 K
Wind speed: 1 – 4 km/h
Acid Rain!
0
20
40
60
80
100
120
Mar
s
Venus
Ear
th
Ar
H2O
O2
N2
CO2
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...and its Moon
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Mars
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Mars: Major Regional Features
MOLA global topography map (Mars Global Surveyor)
northern lowlands
southern highlands
Tharsis
volcanic province
Hellas
impact basin
Valles Marineris
Outflow
channels
seasonal ice cap
(both N and S pole)
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Atmosphere
Composition CO² 95%, N² 2,7%, Ar 1.6%, O²
0.13%
Mass: 2.17.1016 kg
Pressure: 0,006 atm
Temperature: 145 – 300 K (225 K average)
Wind speed: 10-30 km/h (Summer), 20 – 40 km/h (Fall), 60 - 100 km/h (Dust storms)
0
20
40
60
80
100
120
Mar
s
Venus
Ear
th
Ar
H2O
O2
N2
CO2
Chemical Components:
Gas (H, He), Ice (NH3, CH4, H2O),
Rock/Iron
Mars
Ganymede
Jupiter
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What is Planetary Geophysics?
Geophysics is the physics of the Earth and its space environment.
Earth's shape; its gravitational and magnetic fields; its internal structure and composition; its dynamics and their tectonic surface expressions, the generation of magmas, volcanism and rock formation.
A broader definition includes the hydrological cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial relations; and analogous problems associated with the Moon and other planets.
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Geophysical and Geodetical Methods (in a stricter sense)
Altimetry (Radar, Laser)
Gravimetry
Global field, local field
Magnetometry
Global magnetic field, electro-magnetic induction methods, rock and
paleo- magnetism
Seismology
Passive, active
Heat Flow
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Theory of Terrestrial Planets (Thermodynamics)
Interior Structure
Iron-rich core, rocky mantle and crust, phase transitions and chemical layerings,
variations with depth of thermodynamic and transport variables
Interior Dynamics
Core and mantle convection (heat transfer), volcanism, tectonism, magnetic field
generation
Rotation and Tides
Tidal dissipation, Seasons
Evolution
Accretion, differentiation (core formation, outgassing), cooling
Habitability and Life
Feedback to Planetary Evolution?
Important Elements of the Theory
Thermodynamic Properties, State variables
Density, Temperature, Pressure, Composition
Chemical Reactions, Phase Transitions
Energy Sources
Accretion, Differentiation, Radioactive Decay
(235, 238U, 232Th, 40K, 26Al, 60Fe), Tidal Heating
Transport Properties
Viscosity (strongly temperature and pressure
dependent), thermal conductivity, electrical
conductivity
Courtesy A. Plesa
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Technology Challenges for Planetary Exploration
Very limited resources
Power
Mass
Challenging environment
Temperature (Pressure)
Radiation
Communication
Autonomy
High risks – including financial
High demands – quality etc
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Mission Classes
Orbiters, (Fly-bys)
Geodesy, Geophyics packages
Laser altimeters, radio science package, stereo cameras
Goal: Geodetic network, figure of planet, gravity field and in general, explore what is out
there
Magnetometers and plasma packages
Magnetic field, Ionosphere, Magnetosphere
Landers, Networks, Rovers
Seismology, Heat Flow, Rock Magnetism
Sample Return
Rock physical properties (in addition to chemistry, mineralogy)
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Bepi Colombo
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Bepi Colombo
ESA Cornerstone Mission to Mercury
Launch 2016, Arrival 2020
Geodesy, Geophysics package (Laser
Altimeter, Radio Science, Stereo Imaging)
Magnetospheric Orbiter + Magnetometer on
Remote Sensing Orbiter
No lander unfortunately
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InSight
Geophyscial Observatory
Seismology, Heat Flow, Rotation
paramters, Magnetism
Mars Interior Structure
Interior, Evolution and Energy
Balance
NASA Discovery Mission with
European Payload
To be launched 2016
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Netlander
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Page 41 Perspektiven Prof. Dr.Tilman Spohn
Page 42 Perspektiven Prof. Dr.Tilman Spohn
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Mercury Venus Earth Mars
Terrestrial Planets vs Earth! Most important differences: Plate Tectonics and Life
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Earth
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Forms of Mantle Convection
Stein and Hansen 2008
Courtesy of Kai Stemmer+
Magnetosphere
Subduction,
regassing, and
enhanced cooling
Atmosphere
Biosphere
Hydrosphere
Crust
Core
Convective Cooling
Dynamo Action
Mantle
Volcanism Degassing
Space
Erosion by
solar wind;
Impacts
Shielding
Planets are Heat Engines
..that convert thermal into
gravitational, deformational
and magnetic field energy.
But the engine is an integral
part of a complex system!
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Habitability and Plate Tectonics
Many believe that (complex, evolved) life requires plate tectonics to operate
Plate tectonics recycles near surface rock and volatiles with the planet’s
interior through subduction. This helps
to cool the deep interior and to generate a magnetic field in the core
to create geologic diversity, e.g., granitic cratons that will form
continents and continental shelfs
to replenish depleted surface rock as the base for the nutrition chain
to help stabilize the atmosphere temperature in the Carbon Silcate and
other cycles
help generate a magnetic field
Water Cycle
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Planets and Life
Water consumption upon melting
Mantle regassing
Continental Crust
(& lithosphere)
Continental crust production
Dewatering
Free water (pores, cracks)
Water in stable minerals
Höning et al., 2013
Ocean-Continent Subduction Zone
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The model is gauged to the present Earth. Parameters are chosen such that with the present weathering rate, the present mantle water content and continental surface area is recovered
Results
0dt
dAcont
0dt
d
Continental
Surface
Area
Mantle
water
Reducing the weathering rate brings about two more equilibrium points, one unstable and a second stable point. The area of attraction of the dry stable point increases with further decreasing weathering rate .
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Bringing in time
biotic
abiotic abiotic
biotic
Perspectives in Planetary Science
Study the earthlike planets and satellites in the solar system: How do planets work?
Study asteroids and comets and exoplanet systems: How do solar systems form?
Adress the habitability of planets: What is the chance for (primitive) extraterrestrial life? Is life an universal phenomenon or is ours a “Rare Earth”?
How unique is the Earth, the solar system?
Planetary Science, Solar System Science, Astrobiology
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Acknowledgements
I profited from input from Doris Breuer,
Lena Noack, Tina Rückriemen, Wladimir
Neumann, Dennis Höning, Hendrik
Hansen-Goos, Allessandro Airo, Heike
Rauer, and Vlada Stamenkovic
I have used material from various sources
including the new Encyclopedia of the Solar
System ed. Spohn, Breuer, Johnson and
Vol. 10 of the Treatise on Geophysics, a
new edition getting to the market later this
year
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Rosetta
Thank You