Open AccessDoes Europa have a subsurface ocean? Evaluation of the geological evidence
Author(s) -
Pappalardo R. T.,
Belton M. J. S.,
Breneman H. H.,
Carr M. H.,
Chapman C. R.,
Collins G. C.,
Denk T.,
Fagents S.,
Geissler P. E.,
Giese B.,
Greeley R.,
Greenberg R.,
Head J. W.,
Helfenstein P.,
Hoppa G.,
Kadel S. D.,
Klaasen K. P.,
Klemaszewski J. E.,
Magee K.,
McEwen A. S.,
Moore J. M.,
Moore W. B.,
Neukum G.,
Phillips C. B.,
Prockter L. M.,
Schubert G.,
Senske D. A.,
Sullivan R. J.,
Tufts B. R.,
Turtle E. P.,
Wagner R.,
Williams K. K.
Publication year - 1999
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1998je000628
Subject(s) - geology , geophysics , satellite , current (fluid) , tectonics , liquid water , jupiter (rocket family) , geologic record , earth science , paleontology , oceanography , physics , space shuttle , astronomy , aerospace engineering , engineering
It has been proposed that Jupiter's satellite Europa currently possesses a global subsurface ocean of liquid water. Galileo gravity data verify that the satellite is differentiated into an outer H 2 O layer about 100 km thick but cannot determine the current physical state of this layer (liquid or solid). Here we summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data. We describe and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull‐apart bands, chaos, ridges, surface frosts, topography, and global tectonics. An internal ocean would be a simple and comprehensive explanation for a broad range of observations; however, we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm, soft ice with only localized or partial melting. Two different models of impact flux imply very different surface ages for Europa; the model favored here indicates an average age of ∼50 Myr. Searches for evidence of current geological activity on Europa, such as plumes or surface changes, have yielded negative results to date. The current existence of a global subsurface ocean, while attractive in explaining the observations, remains inconclusive. Future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within Europa today.