Internal Heating: Planets and Moons July 21, 2005 Presented to teachers in TRUST by Denton S. Ebel Assistant 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: 40 K, 232 Th, 235 U, 238 U) Tidal friction (only in some cases, e.g.-Io) Solar heating (restricted to surfaces)

Complex and Simple Cratering (images taken from published literature have been removed here)

Early Solar System: Collisions of Small Bodies to Make Bigger Bodies and Eventually Planets (image taken from published literature has been removed here)

Chondritic meteorites contain radionuclides

Abundant Isotopes Extinct: 26 Al => 26 Mg720 K years Present time: 40 K => 40 Ar, 40 Ca1.27 G years 238 U …. 208 Pb4.47 G years 235 U …. 207 Pb704 M years 232 Th …. 208 Pb14.0 G years

Orbital resonance with Europa tugs Io, so Io’s Jupiter-facing side wobbles 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 published literature has been removed here)

Comparing the orbital radius with the gravity of the primary gives an idea of the tidal forces experienced by a Moon. Io

Jupiter’s major moons, seen by Galileo in 1610: Io Europa Ganymede Callisto Earth’s moon, Moon Saturn’s major moon, Titan

Io Europa Ganymede Callisto Voyager missions (1979) showed that each of these moons is a different world. The moons are all ‘tidally locked’, rotate in the same direction in nearly circular orbits in Jupiter’s equatorial plane. They likely formed as a ‘subnebula’ in the solar disk. Moonorbitdensity Io Europa Ganymede Callisto (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 1997September 1997 Pillan Patera volcano outflow on Io, imaged by Galileo spacecraft, km

Io Silicate Mantle 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 Europa Great 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

Galileo Galilei ( ) - 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 Theories 1) 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 published literature 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 –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 N 2 CH 4 Ar surface T: 93.8 K (-180 C)

The End Saturn A Ring UV Imaging Spectrograph dirty = red; icy = turquoise res = 60 miles (97km) Photo # PIA05075

PIA05076 C+B rings