Other
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusm.p31c..03c&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #P31C-03
Other
1028 Composition Of Meteorites (3662, 6240), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5220 Hydrothermal Systems And Weathering On Other Planets, 6207 Comparative Planetology, 6224 Kuiper Belt Objects
Scientific paper
We consider various scenarios for the early chronology of outer solar system icy objects (e.g., planetesimals, satellites, dwarf planets) depending on the time at which these objects formed with respect to the production of calcium-aluminum inclusions. The latter is our time of reference for computing the amount of short-lived radioisotopes accreted in these objects. We especially focus on hydrothermal activity that could have taken place in icy planetesimals and the consequences on the early history of bigger objects depending on the time and duration of accretion, i.e. whether or not short-lived radioisotopes were still in significant abundance in planetesimals when icy satellites and dwarf planets formed. Chemical alteration as a result of 26Al-triggered differentiation has been studied in the case of meteorite parent bodies, but the consequences of such a phenomenon in the case of outer Solar system objects has not been thoroughly addressed. However, various recent observations suggest that the outer Solar system could have formed in a few My after the beginning of the Solar system. In such conditions meteorite parent bodies and icy objects (from planetesimals to large icy objects) could have had a similar early history. Early melting is accompanied by hydrothermal circulation and resulting aqueous alteration and redistribution of major elements between the rock phase and the volatile phase. This can result in partial hydration of the silicate phase, formation of salt compounds in small objects from which molecular hydrogen can easily escape, as well as leaching of long-lived radioisotopes from the rock phase. Melting can also result in the destabilization of clathrate hydrates and thus degassing of major species predicted by cosmochemical models, with implications for the diversity of compositions of planetesimals in the early outer Solar System. We consider several classes of planetesimals, characterized by their size, time of formation, initial rock mass fraction, and volatile composition. The smallest ones are not affected by short-lived radioisotope decay. The medium-sized planetesimals (in the 5-20 km range) are affected by partial melting, while planetesimals several tens of km in radius could be fully differentiated before they accreted into larger objects. We expect that the disruption of differentiated planetesimals during the accretion could lead to chemical segregation. All these processes can have consequences for the long-term evolution of the larger bodies (e.g. salts affect the melting temperature of ice shells, hydrated silicates affect heat transfer through rocky cores). We will present some implications relevant to meteorite parent bodies, small icy satellites, and dwarf planets. Acknowledgements: This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2009 California Institute of Technology. Government sponsorship acknowledged.
Castillo-Rogez Julie
Choukroun Mathieu
Johnson Teresa
Lunine Jonathan
Matson Dennis
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