The Seven Ages of Terrestrial Planetary Science and the Pervasive Contributions of William Kaula

Kaula’s Seven Ages of a Planet 1. Nebular condensation 2. Planetesimal growth 3. Planetary formation 4. Vigorous convection 5. Plate tectonics 6. One-plate volcanism 7. Quiescence

Seven Ages of Terrestrial Planetary Exploration 1. Early Earth satellites 2. Planetary reconnaissance (Mariner flybys) 3. Apollo 4. Global survey of Mars (Viking, MGS) 5. Global survey of Venus (PVO, Magellan) 6. Global survey of the Moon (Clementine, LP) 7. Present era (Mars Surveyor and Discovery Programs

First Age of Terrestrial Planetary Exploration: Early Earth Satellites In the 1960s, William Kaula pioneered the conceptual and analytical tools that established the field of space geodesy. High-school photograph “ And then formation: sweeping up The bodies in its way”

(Kaula, 1966)

Second Age of Terrestrial Planet Exploration: Reconnaissance by Flybys Venus 1962Mariner Mariner 5 Mars 1965Mariner Mariner 6, 7 Mercury Mariner 10 “The first of these is condensation; dust grains drifting to The nebula plane in chondrite clods.” Detail from AAS Division of Dynamical Astronomy meeting photo, 1970

ICARUS 28, (1976)

One scenario for orbital evolution and planetesimal provenance for “Mercury” [Wetherill, 1988]. Mercury May Have Accreted Material from a Range of Solar Distances

Simulation of an off-axis collision of proto- Mercury with a protoplanet one sixth its mass [Benz et al., 1988]. 1. Preferential removal of silicate grains by gas drag. 2. Vaporization of silicate outer layers by an early active Sun. 3. Stripping of silicate outer layers by a giant impact. Competing Hypothesis for the Origin of Mercury’s High Metal/Silicate Ratio

Third Age of Terrestrial Planetary Exploration: Apollo William Kaula served as Principal Investigator for the laser altimeter experiment on Apollo 15, 16, and 17, which provided the first quantitative information on lunar nearside-farside differences. “But heating slows;…mare To surface, ending fractionation.”

Fourth Age of Terrestrial Planetary Exploration: Global Surveys of Mars (Viking, Mars Global Surveyor) William Kaula was the first to show clearly the effect of Tharsis on the global shape of Mars and how to remove its contribution to J 2 to infer C/MR 2. “Final volcanism: no More lithospheric spreading,only vents For magma, Nix Olympica.”

Issues in Martian Internal Structure Core composition, radius, and physical state Nature of core-mantle boundary Implications for mantle plumes Bertka and Fei (1998)

Global Influence of Tharsis The Tharsis rise must have been substantially in place by the Late Noachian, on the basis of its influence on deformation and valley network downslope directions. (Phillips et al. 2000)

Fifth Age of Terrestrial Planetary Exploration: Global Surveys of Venus (PVO, Magellan) William Kaula served on the science teams for both the Pioneer Venus Orbiter and Magellan missions. He made many contributions to an understanding of the comparative evolution of Venus and Earth. Detail from Magellan Radar Investigation Group photo, 1990 “And then comes plate tectonics: cooling leads To lithosphere, with many marginal breaks.”

Crater Retention Ages on Venus Imply Past Lithospheric Recycling Crater Retention Ages on Venus Imply Past Lithospheric Recycling Lithosphere stabilizes by melt extraction then becomes unstable after cooling [Parmentier and Hess, 1992]. Boundary-layer instability for high-Rayleigh-number thermal convection [Turcotte et al., 1999]. Possible recycling mechanisms:

Climate Change May Have Influenced Tectonic Deformation on Venus Climate Change May Have Influenced Tectonic Deformation on Venus Magellan image of ridged plains, Rusalka Planitia (image 150 km wide). Surface thermal stress induced by climate change following emplacement of ridged plains lavas, according to the climate models of Bullock and Grinspoon (2000).

In the 1990s, William Kaula continued to press for key threads that linked the distinct evolutionary tracks of the bodies in the inner solar system. “A planet in its time plays many parts.” Sixth Age of Terrestrial Planetary Exploration: Global Surveys of the Moon (Clementine, Lunar Prospector)

Neumann et al. (1996) Joliff et al. (2000) Global Geophysical and Geochemical Mapping Indicates the Moon is Strongly Heterogeneous

The Seventh Age is Upon Us The NASA MESSENGER mission, to be launched in 2004, will flyby and orbit Mercury and return geochemical information diagnostic of the planet’s formational processes.

The Seventh Age is Upon Us The CNES NetLander mission will send four geophysical and meteorological stations to Mars in Determining the interior structure of Mars requires a surface seismic network.

Kaula 5485 “Last scene That ends this history is quiescence: time Sans melt, sans plates, sans almost everything” William Kaula,

The Seven Ages of a Planet Our system is a stage, And both the Sun and planets merely players. They had their birth and’ll have their fiery end. A planet in its time plays many parts, Its acts being seven ages. The first of these Is condensation: dust grains drifting to The nebula plane in chondrite clods. And then The planetesimals: breaking sometimes, but Most growing, though the Sun’s hot breath blows gas Away. And then formation: sweeping up The bodies in its way, in fierce infalls To bring then full convective vigor, too hot For crust to form, though iron may sink and seas Outgas, by radioactive energy driven. And then comes plate tectonics: cooling leads To lithosphere, with many marginal breaks. Convective thrusts a crust create in belts Complex. But heating slows; the sixth age shifts Into the final volcanism: no More lithospheric spreading, only vents For magma, Nix Olympica or mare To surface, ending fractionation. Last scene That ends this history is quiescence: time Sans melt, sans plates, sans almost everything.