Geoffrey C. Collins

Wheaton College (MA) · Department of Physics

A nearly pole‐to‐pole survey near 140°E longitude on Europa revealed many areas that exhibit past lateral surface motions, and these areas were examined to determine whether the motions can be described by systems of rigid plates moving across Europa's surface. Three areas showing plate‐like behavior were examined in detail to determine the sequenc...

Tectonic pit chains are geologic landforms that form in loose unconsolidated regolith and are observed on many solar system bodies. In the outer solar system they are most clearly observed on Enceladus. In this paper, we test three techniques for using pit chain morphometry to probe the regolith thickness across Enceladus accumulated as fall-back f...

Expressions of strike-slip faulting are well documented on multiple ocean worlds (e.g., Europa, Enceladus, and Ganymede) and the motion along these faults is thought to be driven by variations in diurnal tidal stresses. Titan exhibits a complex and dynamic geology with a varied surface morphology developed from fluvial, aeolian, and possible cryovo...

Laplace‐like resonances among Ganymede, Europa, and Io may have once led Ganymede to have an eccentricity (presently e = 0.0013) as high as ~0.07 (Showman & Malhotra, 1997, https://doi.org/10.1006/icar.1996.5669). While diurnal stresses at Ganymede today are small (less than 10 kPa), a previous period of higher eccentricity may have allowed for an...

The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults. However, the epicentre locations of these quakes are...

In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarchin...

High-resolution Galileo data of Ganymede's complex surface provide strong and ubiquitous evidence of strike-slip motion: en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and strained craters. In a previous study, we performed a detailed mapping of these strike-slip morphologies within nine regions of Ganymede: Da...

The heavily fractured surface of Ganymede displays many morphologically distinctive regions of inferred distributed shear and strike-slip faulting that may be important to the structural development of its surface. To better understand the role of strike-slip tectonism in shaping this complex icy surface, we perform detailed mapping at nine sites u...

Enceladus is the first outer solar system body on which pit chains have been positively identified. We map the global distribution of pit chains and show that pit chains are among the youngest tectonic features on Enceladus's surface, concentrated in the cratered plains centered on Enceladus's Saturnian and anti-Saturnian hemispheres. Pit chains on...

Recent observational evidence points to the existence of plate tectonics on Europa. To date, this is only other body besides Earth to demonstrate active plate tectonics. The evolution of a planetary body’s interior from its hot origins to the present day state dictates surfaces processes ranging from habitability to plate tectonics and provides the...

The surface of Europa is heavily dissected by tectonic features that may act as the boundaries of icy lithospheric plates. Analyses of plate motions on Europa have provided insight into the formation and evolution of specific feature types and provided a means of testing processes and assumptions based on terrestrial plate tectonics. The scale of p...

Based on the Europa Clipper mission concept, NASA's Europa Multiple Flyby Mis- sion, planned for launch in 2022, will perform more than 40 flybys of Europa with altitudes at closest ap- proach as low as 25 km. The instrument payload includes the Europa Imaging System (EIS), a camera suite designed to transform our understanding of Euro- pa through...

Observations of past plate tectonic - like motions in Europa’s icy lithosphere have been reported in previous studies. Quantifying the nature, age, and amount of plate motion is important for geophysical models of Europa’s ice shell and for astrobiology, since subsumed pates could drive the flow of nutrients into the subsurface ocean. We have used...

Lunar Reconnaissance Orbiter Camera images reveal a vast, globally distributed network of over 3200 lobate thrust fault scarps, making them the most common tectonic landform on the Moon. Based on their small scale and crisp appearance, crosscutting relations with small-diameter impact craters, and rates of infilling of associated small, shallow gra...

Grooved terrain on Ganymede consists of distinct areas of parallel to sub-parallel ridges and troughs at a variety of spatial scales. Grooved terrain has been interpreted as the product of tectonism in the form of fault-accommodated distributed lithospheric extension. We use physical analog methods to test the formation of grooved terrain by imbric...

Near the tiger stripes / Boulders are distributed / Exponentially.

The distribution of young thrust fault scarps on the Moon may be the result of global contraction in combination with tidal stresses.

Vertical transport processes across ice shells are important for questions of habitability and planetary protection. We present an inventory of processes, their applications to icy worlds of interest, and disconnects in the vertical transport chain.

Strike-slip tectonism may be important to the development of Ganymede’s surface. Diurnal stress alone cannot drive motion; NSR shear stress may induce creep.

1] Ice resistance to tensile fracture influences surface morphodynamics on outer planetary satellites such as Titan, yet measurements of tensile strength and fracture toughness of polycrystalline water ice at temperatures below terrestrial conditions (<220 K) have not been previously reported. We investigated these parameters from 260 K to 110 K us...

NASA’s exploration of planets and satellites over the past 50 years has led to the discovery of water ice throughout the solar system and prospects for large liquid water reservoirs beneath the frozen shells of icy bodies in the outer solar system. These putative subsurface oceans could provide an environment for prebiotic chemistry or a habitat fo...

Final results from our experiments investigating the abrasion resistance and strength of polycrystalline ice and ice/contaminant mixtures at Titan temperatures allow us to update the calculations of Collins (2005), which examined the ease of fluvial incision into ice bedrock on Titan. If Titan’s stream channels run over exposed bedrock, the rate of...

Fluvial features on Titan have been iden-tified in synthetic aperture radar (SAR) data taken during spacecraft fl ybys by the Cassini Titan Radar Mapper (RADAR) and in Descent Imager/Spectral Radiometer (DISR) images taken during descent of the Huygens probe to the surface. Interpreta-tions using terrestrial analogs and process mechanics extend our...

About a quarter of Jupiter's moon Europa is covered by patches of "chaotic" terrain where some parts of the preexisting surface have been disrupted into "plates" that are tilted and translated, and other parts have been replaced by an irregular hummocky matrix of jumbled ice blocks. Catastrophic ice-fluid interactions on the Earth offer attractive...

Fluvial features on Titan have been inferred in data from surface imaging instruments on the Cassini spacecraft (Image Science Subsystem, ISS; Visual and Infrared Mapping Spectrometer, VIMS; Cassini Titan RADAR Mapper, RADAR) and the Huygens probe (Descent Imager/Spectral Radiometer, DISR). Interpretations of these features using terrestrial classi...

As is the case at many liberal arts colleges, at Wheaton we require all of our students to take a class in the natural sciences. Our introductory classes must include some type of experimental or laboratory component that allows students to directly experience the scientific cycle of asking a question, collecting data, and analyzing the data to eit...

We present measurements of the tensile strength and abrasion susceptibility of pure and impure polycrystalline ice samples, and discuss applications to fluvial erosion on Titan.

Images of the surface of Titan returned by the Cassini-Huygens mission show extensive fluvial drainage networks, which may be eroded by low-velocity impacts by ice clasts moving as bedload in rivers of liquid methane. Recent work has shown that the strength of polycrystalline water ice at Titan surface temperature of 93K is comparable to moderate s...

The surface of Dione exhibits several zones of normal faults that have been imaged by the Cassini ISS. These faults occur in two main clusters. The best imaged cluster of fault zones is near the trailing point, and radiates from this area in the four ordinal directions. Another group near the leading point displays some unusual morphologies, but ha...

We have compiled a global geological map of Ganymede that represents the most recent understanding of the satellite based on Galileo mission results. This contribution builds on important previous accomplishments in the study of Ganymede utilizing Voyager data and incorporates the many new discoveries that were brought about by examination of Galil...

Titan possesses subtle but distinctive structural geological features. We use Cassini's synthetic aperture radar (SAR), HiSAR (a high-altitude single beam imaging mode), and SARTopo data of Titan with emphasis on the structural interpretation of tectonic elements.

Pit crater chains exist on a range of planetary bodies --- from small asteroids to icy moons to large terrestrial planets --- raising important questions about formation mechanisms and near-surface crustal properties of solid bodies in our solar system.

This book describes the tectonic landforms resulting from major internal and external forces acting on the outer layers of solid bodies throughout the Solar System. It presents a detailed survey of tectonic structures at a range of length scales found on Mercury, Venus, the Moon, Mars, the outer planet satellites, and asteroids. A diverse range of...

The tensile strength of ice bedrock on Titan should strongly influence the effectiveness of the erosional processes responsible for carving the extensive fluvial drainage networks and other surface features visible in images returned by the Cassini and Huygens probes. Recent measurements of the effect of temperature on the tensile strength of low-p...

Images from Cassini and Huygens reveal widespread fluvial dissection of Titan's surface, where incision by low-velocity impacts of bedload sediments may be a dominant mechanism, much like fluvial systems on Earth. Models of fluvial erosion dynamics on Titan are currently limited by a lack of data on ice resistance to abrasive wear at ultra-low temp...

Ganymede is unique in that it is the largest satellite in the solar system, the most centrally condensed solid body in the solar system, and the only solid body in the outer solar system known to posses an internally generated magnetic field. At the same time, its surface displays an array of geologic features spanning a wide range of ages and heat...

We have compiled a global geologic map of Ganymede utilizing Galileo mission results. This contribution will help to provide constraints on models of the formation and evolution of Ganymede and potentially the other Galilean satellites.

The outer Solar System contains a great diversity of planets and satellites. Cassini (a Flagship class mission) is now completing exploration of the Saturn system; New Horizons (New Frontiers class) is en route to the first encounter with the Pluto-Charon system in 2015, pressing onward into the Kuiper belt thereafter; and Juno (New Frontiers class...

Four hundred years after Galileo Galilei's earth-moving discovery, Europa once again has a profound scientific importance. Data from the Galileo spacecraft revealed that Europa's icy surface likely hides a global subsurface ocean with volume nearly three times that of Earth's oceans. The existence of liquid water in the outer solar system was once...

Ganymede is the largest satellite in the solar system, and is one of only three solid bodies in the solar system that is known to possess an internally generated magnetic field. This field is contained within Jupiter's strong field, creating a unique laboratory for studying magnetic reconnection and other magnetospheric interaction processes. The m...

Existing methods to quantify angiogenesis range from image analysis of photographs to fluorescent microscopy. These methods are often time consuming and costly; they also may not detect capillaries if they are indistinct from the background of the image. We have developed a simple method based on the motion of blood to create an image that reveals...

The tidal stress at the surface of a satellite is derived from the gravitational potential of the satellite's parent planet, assuming that the satellite is fully differentiated into a silicate core, a global subsurface ocean, and a decoupled, viscoelastic lithospheric shell. We consider two types of time variability for the tidal force acting on th...

In this presentation we display the calculated surface strain over fault sets on Dione, and provide an analysis of the overall surface strain accommodated on Dione.

We have converted spectrometer data from Cassini VIMS and Galileo NIMS into GIS layers that can be queried along with geological map data. This presentation shows examples from CO2 band depth mapping on Dione and Ganymede.

All airless planetary surfaces in our Solar System appear to be covered by a regolith layer. There are several general processes that could form such a regolith layer, including the rain of impactors on the surface, mass wasting, sublimation degradation, and physical weathering by thermal changes. Several of these processes have been well studied o...

Rock resistance to fluvial abrasion by bedload sediment impacts has been shown experimentally to depend on the square of rock tensile strength across the full range of rock strengths encountered in the field. This result is consistent with fracture mechanics theory which predicts that fractures propagate when the capacity of brittle materials to st...

The Pluto-Charon binary dwarf planet system is probably the result of an impact of similar-sized Kuiper Belt objects. The pair evolved from an unknown initial state to the dynamical end state in which we find them now, synchronously locked to each other. In this presentation, we investigate the implications of the evolution to this end state for th...

The surface of Enceladus displays a collection of pit-chains. We discuss various potential causes to their origin, including the drainage of unconsolidated surface material into dilational-fault-induced voids, which we believe to be the most likely explanation.

Using estimated rainfall rates and stream discharge rates we are attempting to narrow down the value for surface runoff coefficients on Titan at the Huygens landing site.

After mapping craters and fractures in ArcGIS we analyzed fracture orientation and crater elongation; graphing these results allowed us to quantify the amount of surface strain on Enceladus.

Results will be presented from a comparison of theoretical models for grooved terrain formation on Ganymede to the strain history represented by the grooves.

Images returned by the Cassini-Huygens mission reveal evidence for widespread fluvial incision in the polar regions of Titan. Dendritic channel networks draining to large lakes and the absence of cratering suggest active incision into Titan's water-ice bedrock surface. Previous work using the saltation-abrasion bedrock incision model suggests that...

Ganymede and Callisto are planet-sized moons of Jupiter, with surfaces composed of a mixture of dark dust and bright ice. Similar in size, they both have interiors of half ice and half rock/metal, but Ganymede's interior appears to be segregated by density, while Callisto's interior is mostly mixed. Both moons appear to have subsurface liquid water...

Galileo's observations in the 1600's of the dynamic system of Jupiter and its moons launched a revolution in understanding the way planetary systems operate. Now, some 400 years later, the discovery of extra solar planetary systems with Jupiter-sized bodies has led to a similar revolution in thought regarding how these systems form and evolve. From...

The Jupiter System Observer (JSO) is one of four studies commissioned by NASA's Science Mission Directorate to examine the potential science return from a flagship-class mission to the outer solar system. JSO is a long-duration mission that will study the entire Jupiter system, focusing on both its individual components, including Jupiter's atmosph...

Recent observations of the south pole of Saturn's moon Enceladus by the Cassini spacecraft have revealed an active world, powered by internal heat. In this paper, we propose that localized subsurface melting on Enceladus has produced an internal south polar sea. Evidence for this localized sea comes from the shape of Enceladus, which does not match...

A global database of grooved terrain packets has been mapped and classified, and this will be used to show a preliminary global surface strain estimate for Ganymede. Relative age sorting of grooves will also be discussed.

We have constructed a global crater database as part of the global geologic map of Ganymede, and we compare different schemes for classifying the craters by age and morphology.

We used strain measurement techniques based on fault geometry as an independent check on strain measurements derived from deformed craters on Ganymede. The techniques agree, and offer a way to estimate strain in more areas of grooved terrain.

By considering the effect of internal melting, we can reconcile the shape of Enceladus with the anomalous south polar heat flow and a differentiated internal structure. Isolated seas may be stable for long time periods beneath the ice on Enceladus.

A significant fraction of icy satellites appear to have an ice shell decoupled from the moon's solid interior by a global ocean. Such satellites when in an eccentric orbit will experience diurnal tidal deformation and stresses within the shell. Further, non-synchronous rotation (NSR) of decoupled ice shells has been suggested as a potential source...

Traditional applications of passive reflectance or emission spectroscopy are poorly suited for astrobiology of icy satellite surfaces, because ice is strongly absorbing and masks spectral regions where organics are active. Two recent Flagship missions, Galileo and Cassini, observed Europa with multiple instruments but failed to detect any organic m...

If the thermal energy radiating from the south polar area of Enceladus is supplied over a limited area at the base of the ice shell, melting of a localized pool of water is favored over convection if the ice begins in conductive equilibrium. We show through numerical modeling that a melt pool produced by the observed excess heat flux from the south...