Large Impact Features on Europa: Results of the Galileo Nominal Mission

Moore, Jeffrey M.; Asphaug, Erik; Sullivan, Robert; Klemaszewski, J. E.; Bender, K.; Greeley, R.; Geissler, P. E.; McEwen, A. S.; Turtle, E. P.; Phillips, C. B.; Tufts, B. R.; Head, J. W.; Pappalardo, R.; Jones, Kathleen W.; Chapman, C. R.; Belton, M. J. S.; Kirk, Randolph L.; Morrison, David

doi:10.1006/icar.1998.5973

Cited by 110 publications

(88 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The topography was derived from stereo (Schenk, 2002) and has a horizontal resolution of 80 m/pixel and an estimated vertical precision of 17 m. The flat floor and raised rim of the crater are indicated in Fig. 2; pedestal deposits exterior to the rim are raised by w100 m relative to the surrounding terrain (Moore et al, 2001). Just to the west of the crater is a triangular area about 10 km along each side, bounded by troughs (blue) to the N and E. The northern trench is both linear and relatively sharp, and trends ENE.…”

Section: Observationsmentioning

confidence: 99%

See 1 more Smart Citation

Normal faulting on Europa: implications for ice shell properties

Nimmo¹,

Schenk²

2006

Journal of Structural Geology

View full text Add to dashboard Cite

We identify two likely normal faults on Europa, of lengths z30 and 11 km. A simple flexural model of fault-related topography gives effective elastic thicknesses of 1.2 and 0.15 km, respectively, and the resulting inferred fault strength is of order 1 MPa. The maximum fault displacement: length ratio for each fault is z0.02, comparable with values on silicate planets. We combine this observation with a modified linear elastic fracture mechanics model to conclude that the shear modulus of the Europan surface must be significantly less than that for unfractured ice. The low value of the modulus is probably due to near-surface fracturing or porosity, which will affect the material's radar properties and seismic velocities. For a likely reduction in shear modulus of an order of magnitude, the driving stresses inferred are about 6e8 MPa, much higher than present-day diurnal tidal stresses. However, stresses approaching these values can be generated by non-synchronous rotation or polar wander, while stresses exceeding these values arise during ice shell freezing. If the entire larger fault breaks, it will generate an event of seismic magnitude M s z5.3.

show abstract

Section: Observationsmentioning

confidence: 99%

“…To the north, this fracture appears to truncate the main northern scarp; to the south, the fracture merges with a number of other fractures to ultimately form a prominent graben (regional images 11E012 and 11E014, not shown). The dark material to the north-east is the continuous ejecta unit of Moore et al (2001).…”

Section: Observationsmentioning

confidence: 99%

Normal faulting on Europa: implications for ice shell properties

Nimmo¹,

Schenk²

2006

Journal of Structural Geology

View full text Add to dashboard Cite

show abstract

“…A wide range of imaging data also suggests the presence of an ocean, including the sparsity of impact craters; lowsurface relief with lateral separation of crustal plates [Lucchita and Soderblom, 1982;Greeley et al, 1998]; models for the formation of flexi by periodic tidal stresses [Hoppa et al, 1999]; and crater morphologies [Moore et al, 1998;Turtle et al, 1999]. The young age (50 My) of Europa's surface, determined from impact crater densities, argues for ongoing geological activity [Zahnle et al, 1998;Levison et al, 2000].…”

Section: Introductionmentioning

confidence: 99%

Persistence of thin ice regions in Europa's ice crust

Buck

Chyba

Goulet

et al. 2002

Geophysical Research Letters

View full text Add to dashboard Cite

[1] Extensive data from planetary spacecraft as well as celestial mechanics models support the existence of a subsurface ocean on Europa $100 km thick, maintained by a tidal heat flux. Models in which the overlying ice crust is less than 20 km thick permit breaches in the ice due to impact events or thermal plumes from the tidally heated core. We apply a two-dimensional thermal model to the analysis of the refreezing of a hole in the ice crust following a breach event. Our model incorporates heat produced by tidal heating of Europa in two ways: a basal heat flux from Europa's silicate and iron core, together with volumetric heating of the ice shell. We compare our refreezing timescales to those obtained from a model where viscous flow in the base of the ice crust fills the hole. We find that catastrophic breaches in Europa's ice crust may produce regions of relatively thin ice persisting up to $1 My. These breaches are closed by viscous flow when radii are small (<10-50 km) and by conductive refreezing for larger radii, especially if Europa's crust has a high basal heat flow due to a hot core. Detection of the ice/ocean interface by orbital detection of the temperature anomalies or radar sounding would be most probable in the vicinity of these events.

show abstract

“…However, rays on icy satellites may be bright because they consist of fine-grained frost [Chapman and McKinnon, 1986]. The rays of the crater Pwyll on Europa extend for thousands of kilometers away from the impact site but, in high-resolution images, are seen to produce minimal disruption of the underlying surface material aside from the change in albedo [Moore et al, 1998]. We thus posit that these crater rays, while clearly different in initial formation mechanism, might be similar to a thin deposit created by an active plume venting water and gas at Europa's surface.…”

Section: Change Detection Resultsmentioning

confidence: 99%

The search for current geologic activity on Europa

Phillips¹,

McEwen²,

Hoppa³

et al. 2000

J. Geophys. Res.

Self Cite

View full text Add to dashboard Cite

Abstract. Observational evidence and theoretical arguments suggest that Jupiter's satellite Europa could be geologically active and possess an "ocean" of liquid water beneath its surface at the present time. We have searched for evidence of current geologic activity on Europa in the form of active plumes venting material above the surface and by comparison of Voyager and Galileo images to look for any changes on the surface. So far, we have observed no plumes and have detected no definitive changes. The lack of observed activity allows us to estimate a maximum steady state surface alteration rate of 1 km 2 y-• in the regions analyzed, assuming alterations will cover contiguous areas of at least 4 km 2 over a period of 20 years. Assuming this as a constant, globally uniform resurfacing rate leads to a minimum average surface age of 30 million years. We also suggest that the lack of obvious circular albedo patterns on the surface due to plumes, coupled with the presence of bright-rayed craters such as Pwyll and the predicted sputtering erosion rate, implies that no large-scale plume activity has taken place over at least the last few thousand years. We thus conclude that if Europa's surface is currently active, any changes must be relatively small in spatial scale or episodic in nature rather than continuous. To detect potential small-scale surface changes, we need high-resolution comparisons between the Galileo data and future Europa Orbiter images.

show abstract

Large Impact Features on Europa: Results of the Galileo Nominal Mission

Cited by 110 publications

References 30 publications

Normal faulting on Europa: implications for ice shell properties

Normal faulting on Europa: implications for ice shell properties

Persistence of thin ice regions in Europa's ice crust

The search for current geologic activity on Europa

Contact Info

Product

Resources

About