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9 - Impact Cratering of Mercury
- Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
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- Book:
- Mercury
- Published online:
- 10 December 2018
- Print publication:
- 20 December 2018, pp 217-248
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Summary
Impact craters are the dominant landform on Mercury and range from the largest basins to the smallest young craters. Peak-ring basins are especially prevalent on Mercury, although basins of all forms are far undersaturated, probably the result of the extensive volcanic emplacement of intercrater plains and younger smooth plains between about 4.1 and 3.5 Ga. This chapter describes the geology of the two largest well-preserved basins, Caloris and Rembrandt, and the three smaller Raditladi, Rachmaninoff, and Mozart basins. We describe analyses of crater size–frequency distributions and relate them to populations of asteroid impactors (Late Heavy Bombardment in early epochs and the near-Earth asteroid population observable today during most of Mercury’s history), to secondary cratering, and to exogenic and endogenic processes that degrade and erase craters. Secondary cratering is more important on Mercury than on other solar system bodies and shaped much of the surface on kilometer and smaller scales, compromising our ability to use craters for relative and absolute age-dating of smaller geological units. Failure to find “vulcanoids” and satellites of Mercury suggests that such bodies played a negligible role in cratering Mercury. We describe an absolute cratering chronology for Mercury’s geological evolution as well as its uncertainties.
6 - The Geologic History of Mercury
- Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
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- Book:
- Mercury
- Published online:
- 10 December 2018
- Print publication:
- 20 December 2018, pp 144-175
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We assess Mercury’s geologic history, focusing on the distribution and origin of terrain types and an overview of Mercury’s evolution from the pre-Tolstojan through the Kuiperian Period. We review evidence for the nature of Mercury’s early crust, including the possibility that a substantial portion formed by the global eruption of lavas generated by partial melting during and after overturn of the crystalline products of magma ocean cooling, whereas a much smaller fraction of the crust may have been derived from crystal flotation in such a magma ocean. The early history of Mercury may thus have been similar to that of the other terrestrial planets, with much of the crust formed through volcanism, in contrast to the flotation-dominated crust of the Moon. Small portions of Mercury’s early crust may still be exposed in a heavily modified and brecciated form; the majority of the surface is dominated by intercrater plains (Pre-Tolstojan and Tolstojan in age) and smooth plains (Tolstojan and Calorian) that formed through a combination of volcanism and impact events. As effusive volcanism waned in the Calorian, explosive volcanism continued at least through the Mansurian Period; the Kuiperian Period was dominated by impact events and the formation of hollows.
The Study of Mercury
- Louise M. Prockter, Peter D. Bedini
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- Journal:
- Proceedings of the International Astronomical Union / Volume 6 / Issue S269 / January 2010
- Published online by Cambridge University Press:
- 03 November 2010, pp. 141-154
- Print publication:
- January 2010
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When the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft enters orbit about Mercury in March 2011 it will begin a new phase in an age-old scientific study of the innermost planet. Despite being visible to the unaided eye, Mercury's proximity to the Sun makes it extremely difficult to observe from Earth. Nonetheless, over the centuries man has pursued a quest to understand the elusive planet, and has teased out information about its motions in the sky, its relation to the other planets, and its physical characteristics. A great leap was made in our understanding of Mercury when the Mariner 10 spacecraft flew past it three times in the mid-1970s, providing a rich set of close-up observations. Now, three decades later, The MESSENGER spacecraft has also visited the planet three times, and is poised to add significantly to the study with a year-long orbital observation campaign.
6 - Tectonics of small bodies
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- By Peter C. Thomas, Center for Radiophysics and Space Research, Cornell University, Ithaca, Louise M. Prockter, Applied Physics Laboratory, Laurel
- Edited by Thomas R. Watters, Smithsonian Institution, Washington DC, Richard A. Schultz, University of Nevada, Reno
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- Book:
- Planetary Tectonics
- Published online:
- 30 March 2010
- Print publication:
- 17 December 2009, pp 233-263
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Summary
Solar system bodies smaller than ~200 km mean radius have little internal heat energy to drive tectonics typical of the terrestrial environment. Short-lived high stresses from impacts or long-term, low stresses are the primary shapers of these bodies. This chapter provides an overview of the basic features and processes that can be regarded as small-body tectonics.
Introduction: types of small bodies, their properties, and environments
Small bodies of the solar system are here taken to be those too small for gravitationally driven viscous relaxation to have determined their shapes. This definition restricts consideration to objects less than about 150 km radius (Johnson and McGetchin, 1973; Thomas, 1989). Within this definition are some dozens of satellites of planets, and thousands of asteroids, cometary nuclei, and Centaur and Kuiper-Edgeworth belt objects (Binzel et al., 2003). As of early 2006, spacecraft have visited small satellites, asteroids, and four cometary nuclei (Figure 6.1). Resolved information on these objects is dominated by the NEAR mission that orbited and then landed on 433 Eros, by images of the Martian satellites, Phobos and Deimos, and by images of comet Tempel 1 (A'Hearn et al., 2005). Radar images of near-Earth objects are beginning to show some details of asteroid shapes and surface features (Hudson et al., 2003). Meteorites provide small samples of asteroids, though only in the case of asteroid Vesta (larger than the size range considered here) are there positive connections of meteorite samples to a specific object (Binzel et al., 1993; Keil, 2002).
7 - Tectonics of the outer planet satellites
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- By Geoffrey C. Collins, Wheaton College, Norton, William B. McKinnon, Washington University, Saint Louis, Jeffrey M. Moore, NASA Ames Research Center, Moffett Field, Francis Nimmo, University of California, Santa Cruz, Robert T. Pappalardo, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Louise M. Prockter, Applied Physics Laboratory, Laurel, Paul M. Schenk, Lunar and Planetary Institute, Houston
- Edited by Thomas R. Watters, Smithsonian Institution, Washington DC, Richard A. Schultz, University of Nevada, Reno
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- Book:
- Planetary Tectonics
- Published online:
- 30 March 2010
- Print publication:
- 17 December 2009, pp 264-350
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Summary
Tectonic features on the satellites of the outer planets range from the familiar, such as clearly recognizable graben on many satellites, to the bizarre, such as the ubiquitous double ridges on Europa, the twisting sets of ridges on Triton, or the isolated giant mountains rising from Io's surface. All of the large and middle-sized outer planet satellites except Io are dominated by water ice near their surfaces. Though ice is a brittle material at the cold temperatures found in the outer solar system, the amount of energy it takes to bring it close to its melting point is lower than for a rocky body. Therefore, some unique features of icy satellite tectonics may be influenced by a near-surface ductile layer beneath the brittle surface material, and several of the icy satellites may possess subsurface oceans. Sources of stress to drive tectonism are commonly dominated by the tides that deform these satellites as they orbit their primary giant planets. On several satellites, the observed tectonic features may be the result of changes in their tidal figures, or motions of their solid surfaces with respect to their tidal figures. Other driving mechanisms for tectonics include volume changes due to ice or water phase changes in the interior, thermoelastic stress, deformation of the surface above rising diapirs of warm ice, and motion of subsurface material toward large impact basins as they fill in and relax.