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
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.