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Internal Heating: Planets and Moons
July 21, 2005
Presented to teachers in TRUST
by Denton S. EbelAssistant Curator, Meteorites
Department of Earth and Planetary Sciences
Heat Sources of Planetary Bodies
Primordial Gravitational potential energy (differentiation) Accretion or collision energy (external source)
Contemporary Decay of radioactive elements (all rocky planets)
(probably 60-80% of Earth’s heat flow: 40K, 232Th, 235U, 238U)
Tidal friction (only in some cases, e.g.-Io) Solar heating (restricted to surfaces)
Complex and Simple Cratering
(images taken from publishedliterature have been removed here)
Early Solar System:Collisions of Small Bodies
to Make Bigger Bodiesand Eventually Planets
(image taken from publishedliterature has been removed here)
Chondritic meteorites contain radionuclides
Abundant Isotopes
Extinct: 26Al => 26Mg 720 K years
Present time:40K => 40Ar, 40Ca 1.27 G years238U …. 208Pb 4.47 G years235U …. 207Pb 704 M years232Th …. 208Pb 14.0 G years
Orbital resonance with Europa tugs Io, so Io’s Jupiter-facing sidewobbles slightly. These tidal forces generate heat by internal friction.
From The New Solar System,Beatty, Petersen & Chaikin (1999),Cambridge U. Press, ch. 17 fig. 5
Tidal Heating of Io
(image taken from publishedliterature has been removed here)
Comparing the orbital radius with the gravity of the primary givesan idea of the tidal forces experienced by a Moon.
0
20000
40000
60000
80000
100000
120000
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160000
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Moon - Io - Europa - Titan
orbi
t R /
prim
ary
equa
tori
al g
orbitR/priGeq
Io
Jupiter’s major moons, seen by Galileo in 1610: Io Europa Ganymede Callisto
Earth’s moon, MoonSaturn’s major moon, Titan
Io
Europa
Ganymede
Callisto
Voyager missions (1979)showed that each of thesemoons is a different world.
The moons are all ‘tidallylocked’, rotate in the samedirection in nearly circularorbits in Jupiter’s equatorialplane. They likely formed asa ‘subnebula’ in the solar disk.
Moon orbit densityIo 5.9 3.5Europa 9.4 3.0Ganymede 15.0 1.9Callisto 26.4 1.8 (orbits are in Jupiter radii)
Asteroid belt(meteorites)
Pluto-Kuiper belt(short period comets)
Our Solar System
Io
Pele’s plume,300 km high(Voyager 1, 1979)
Plan Patera plume, 140 km(Galileo spacecraft 1997)
Prometheus plume(Galileo spacecraft 1997)
Pele volcano on Io (Galileo spacecraft image, 1997)
Io
April 1997 September 1997
Pillan Patera volcano outflow on Io, imaged by Galileo spacecraft, 1997
400 km
Io
SilicateMantle
Silicate - sulfur crust
FeS?Core
Inside Io
(maybe)
Europa
Crater on Europa
Streaks on Europa
Streaks -fractures filled with ice.
Streaks on Europa
Ice Rafts on EuropaGreat rafts of ice in re-frozen surface (view width ~70 km)
Deformation of Europa
Four possible processes:
1 - upwarping
2 - surface fractures
3 - upwelling & fluid flow
4 - collapse to chaotic terrain
Crater on Europa
FeS?
Core
silicate
Silicate + ice
water ice crust
Europa inside(maybe)
Photo #: IV-121-M Mission: Lunar Orbiter IV Date: 1967
Photo #: IV-138-M
The Moon
The Moon• Galileo Galilei (1564-1642) - observed the
moon through a telescope and called the dark smooth areas maria (latin for seas) and the lighter colored, rugged terrain, he called terrae (latin for lands).
• Aside from the Earth the moon is the best understood planetary body in the solar system.
• Many of our current theories and hypotheses of how the Earth and other planets formed were developed and tested by studying the moon.
Dr. Harrison Schmitt,astronaut on Apollo 17
Large split boulder at Taurus-Littrow landing site
Moon Formation Theories1) Co-accretion in orbit while Earth formed.2) Capture - Moon formed elsewhere in the
nebula but was captured by Earth’s gravity.
3) Giant Impact.
• Observations that need to be explained• Chemically the moon is similar to Earth’s mantle• The moon lacks the more volatile elements• Moon’s metal core, if present< is relatively small• Oxygen isotopes are similar to the earth.
Schematic of Moon Forming Impact
(image taken from publishedliterature has been removed here)
Radiometric Dates for the Moon
• Absolute ages determined by radiometric dating of rocks from the moon.
• Basaltic lavas are 3.65 to 4.0 billion years old.
• Lunar highlands are more than 4.5 billion years old.– Indicates that the terrae formed shortly after
accretion of the moon.
• Some ray material from Copernicus is less than 1 billion years old.
• Integrating these ages into the relative scale allows the development of an absolute scale.
Rate of Cratering and Volcanism with Time
• Rate of cratering was much more intense in the earlier periods of lunar history.
• The decline in the amount of impact events was rapid after about 3 billion years ago.
• It is assumed that this is representative of the cratering history of all planets including the Earth.
• Based on radiometric ages, volcanism lasted about one billion years between 4.0 and 3.2 billion years ago.
• Some lavas are 2.5 billion years old but may be melt generated by impact.
Lunar chronology of Crater Copernicus region.
Shoemaker and Hackman (1962)
Copernicus
Erastothenes
Kepler
Mare Imbrium
Crater Copernicus• Copernicus
– Bright rays extend over 300 km.– Rays extend across Procellarum and Mare
Imbrium.– Rays cut across the floor of Erastothenes. – Craters Kepler and Aristarchus have similar
patterns of rays to those of Copernicus.
•Therefore Copernicus ( and Kepler and Aristarchus) are younger than Erastothenes and the basalts of Mare Imbrium).
Crater Erastothenes• Erastothenes
– Found on the lunar maria– Terraced walls– Circular floor– Central peak – Small secondary craters– No visible rays
•Therefore, Erastothenes is younger than the maria and older than the rayed craters.
Imbrium Basin• Imbrium Basin
– Large multi-ring basin– Filled by lunar maria
•Craters like the Imbrium Basin are older than the lunar maria and craters like Erostathenes
– This period of muilti-ring craters and extrusions of the lunar maria is known as the Imbrium Period
Ejecta from the Imbrium Basin overlap craters like the Nectarian Basin in the lunar highlands.
Titan
Artist rendering of Huygens probe descending into Titan
N2
CH4
Ar
surface T: 93.8 K (-180 C)
The End
Saturn A RingUV Imaging Spectrographdirty = red; icy = turquoise
res = 60 miles (97km)Photo # PIA05075
PIA05076 C+B rings
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