TECTONIC PROCESSES ON EUROPA - TIDAL STRESSES, MECHANICAL RESPONSE, AND VISIBLE FEATURES

Citation
R. Greenberg et al., TECTONIC PROCESSES ON EUROPA - TIDAL STRESSES, MECHANICAL RESPONSE, AND VISIBLE FEATURES, Icarus (New York, N.Y. 1962), 135(1), 1998, pp. 64-78
Citations number
39
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Astronomy & Astrophysics
ISSN journal
0019-1035
Volume
135
Issue
1
Year of publication
1998
Pages
64 - 78
Database
ISI
SICI code
0019-1035(1998)135:1<64:TPOE-T>2.0.ZU;2-N
Abstract
Europa's orbital eccentricity, driven by the resonance with Io and Gan ymede, results in ''diurnal'' tides (3.5-day period) and possibly in n onsynchronous rotation. Both diurnal variation and nonsynchronous rota tion can create significant stress fields on Europa's surface, and bot h effects may produce cracking. Patterns and time sequences of apparen t tectonic features on Europa include lineaments that correlate with b oth sources of stress, if we take into account nonsynchronous rotation , after initial crack formation, by amounts ranging up to several tens of degrees. For example, the crosscutting time sequence of features i n the Cadmus and Mines Linea region is consistent with a combined diur nal and nonsynchronous tensile-stress field, as it evolves during tens of degrees of nonsynchronous rotation. Constraints on the rotation ra te from comparing Voyager and Galileo images show that significant rot ation requires >10(4) yr, but could be fast enough to have allowed sig nificant rotation since the last global resurfacing, even if such resu rfacing was as recent as a few million years ago. Once cracking is ini tiated, diurnal tides work cracks so that they open and close daily. A lthough the daily effect is small, over 10(5) yr double ridges could p lausibly be built along the cracks with sizes and morphologies consist ent with observed structures, according to a model in which underlying liquid water fills the open cracks, partially freezes, and is extrude d during the daily closing of the cracks. Thus, several lines of obser vational and theoretical evidence can be integrated if we assume nonsy nchronous rotation and the existence of a liquid water layer. (C) 1998 Academic Press.