Laboratory models suggest that stretching forces shaped Ganymede's surface

An image of a tabletop-size analogue model (left) shows details of fault systems created by extension that visually match an image by spacecraft Galileo of faulted terrain on Ganymede (right). 

Credit: Left Image: Courtesy of Southwest Research Institute; 

Right Image: Courtesy of NASA/JPL SSI

Processes that shaped the ridges and troughs on the surface of Jupiter's icy moon Ganymede are likely similar to tectonic processes seen on Earth, according to a team of researchers led by Southwest Research Institute (SwRI).

To arrive at this conclusion, the team subjected physical models made of clay to stretching forces that simulate tectonic action. The results were published in Geophysical Research Letters.

Physical analogue models simulate geologic structures in laboratory settings so that the developmental sequence of various phenomena can be studied as they occur.

The team, including researchers from SwRI, Wheaton College, NASA's Jet Propulsion Laboratory and NuStar Energy LP, created complex patterns of faults in their models, similar to the ridge and trough features seen in some regions of Ganymede.

The models consisted of a "wet clay cake" material possessing brittle characteristics to simulate how the icy moon's lithosphere, the outermost solid shell, responds to stresses by cracking.

The laboratory models suggest that characteristic patterns of ridges and troughs, called grooved terrain on Ganymede, result from its surface being stretched.

"The physical models showed a marked similarity to the surface features observed on Ganymede," said co-author Dr. Danielle Wyrick, a senior research scientist in the SwRI Space Science and Engineering Division.

"From the experiments, it appears that a process in which the crust breaks into separate blocks by large amounts of extension is the primary mechanism for creating these distinct features."

"Physical analogue modeling allows us to simulate the formation of complex three-dimensional geological structures on Ganymede, without actually going to Ganymede," said co-author Dr. David Ferrill, director of the Earth, Material and Planetary Sciences Department in the SwRI Geosciences and Engineering Division.

"These scaled models are able to reproduce the fine geometric details of geologic processes, such as faulting, and to develop and test hypotheses for landscape evolution on planetary bodies."

SwRI researchers previously have used physical analog models to examine the process by which pit crater chains, a series of linear pits, or depressions, develop on Mars, and how magma in the Martian subsurface deforms the surface of the Red Planet.

More information: The paper, "Physical models of grooved terrain tectonics on Ganymede," by D.W. Sims, D.Y. Wyrick, D.A. Ferrill, A.P. Morris, G.C. Collins, R.T. Pappalardo and S.L. Colton, was published by Geophysical Research Letters, 16 June 2014, Volume 41, Issue 11, pages 3774–3778, DOI: 10.1002/2014GL060359

Time Warp: Event-hiding 'temporal cloak' demonstrated

Last year researchers at Imperial College London proposed that along with being used to cloak physical objects metamaterials could also be used to cloak a singular event in time.

A year later, researchers from Cornell University have demonstrated a working "temporal cloak" that is able to conceal a burst of light as if it had never occurred.

In a research paper published in the Journal of Optics last year, Prof. Martin McCall and his team at Imperial College London said it should be theoretically possible to create a "Spacetime Cloak" by using metamaterials - a class of artificial materials engineered to have properties not be found in nature - to speed up the leading edge of light waves, while slowing down the trailing half.

This would create a "corridor" between the two halves, at which point their source wouldn't be observable.

To demonstrate the theory, a Cornell research team led by Moti Fridman sent a beam of light down an optical fiber and passed it through a split-time lens - a silicon device originally designed to speed up data transfer.

As the beam passes through the first lens it is compressed, leaving a dead zone or gap in the flow of light.

A similar lens further along the path reverses the velocity adjustments, decompressing the light wave so it appears that the light coming through the second lens is uninterrupted as if no distortion had occurred.

To test the temporal cloak's performance the researchers created pulses of light directly between the two lenses that repeated like clockwork at a rate of 41 kHz.

When the cloak was off, the researchers were able to detect a steady beat, but after switching on the cloak, which was synchronized with the light pulses, it appeared as if the pulses were erased from the data stream.

Rather than relying on the properties of metamaterials as was initially proposed by McCall, the temporal cloak demonstrated by the Cornell research team relies on the fundamental properties of light and how it behaves under highly constrained space and time conditions.

The length of the cloaked area is a mere six millimeters (0.2 in) long and the effect can only lasts for 110 nanoseconds.

The team says the best it can achieve will be 120 microseconds because longer durations would create turbulence in the system that would hint that an event had occurred.

To achieve any measurable macroscopic effects would require an experiment on planetary or even interplanetary scales, the researchers say.

The Cornell team will present their findings in a presentation "Demonstration of Temporal Cloaking" at the Optical Society's Annual Meeting, Frontiers in Optics (FiO) 2011, being held in San Jose, California, next week.

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