New model could offer an explanation for cracks like the one on Charon
A new model developed by 人妻少妇专区 researchers could offer a new explanation as to how cracks on icy moons, such as Pluto鈥檚 Charon, formed.
Until now, it was thought that the cracks were the result of geodynamical processes, such as plate tectonics, but the models run by Alice Quillen and her collaborators suggest that a close encounter with another body might have been the cause.
Astronomers have long known that the craters visible on moons were caused by the impact of other bodies, billions of years ago. But for every crash and graze, there would have been many more close encounters. By devising and running a new computer model, Quillen, a professor of physics and astronomy at Rochester, has now shown that the tidal pull exerted by another, similar object could be strong enough to crack the surface of such icy moons. Quillen also thinks that 鈥渋t might even offer a possible explanation for the crack on Mars, but that鈥檚 much harder to model.鈥�
Icy moons exhibit what is know as brittle elastic behavior, which Quillen says most resembles 鈥渟illy putty.鈥�
鈥淚f you take silly putty and throw it on the floor it bounces 鈥� that鈥檚 the elastic part,鈥� said Quillen. 鈥淏ut if you pull on it rapidly and hard enough, it breaks apart.鈥�
To simulate the behavior, Quillen modeled the icy moons as if their interior was made up of many bodies connected by springs (an N-body problem with springs). While N-body problems are often used to understand the effect of gravity on planets and stars, N-body problems had never been used to model the inside of an astronomical body, in this case the moons. Other models for icy moons used what are known as 鈥渞ubble pile models.鈥�
鈥淚 was inspired by computer graphics code in how to model the icy moons,鈥� said Quillen. 鈥淭he inside of the moons is similar to how blood splatter is modeled in games and the outer, icy crust is similar to modeling clothes and how they move. But I, of course, had to ensure the code matched the underlying physics!鈥�
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Simulations done by Alice Quillen showing how different bodies would react to close tidal encounters, including when modeling only the cores of the icy moons and how cracks occur when the top, icy layer is added.
To ensure her model took into account the right properties for the materials that make up the moons, she worked with earth sciences Professor Cynthia Ebinger.
鈥淚 jumped at the opportunity to consider a novel alternative to plate tectonics, the governing theory to explain earthquakes, volcanoes and moving plates on Earth,鈥� said Ebinger. 鈥淢y role was to provide some checks and balances to Alice鈥檚 modeling and the choice of model parameters.鈥�
In the paper, to be published by the journal Icarus, Quillen states that 鈥渟trong tidal encounters鈥� may be responsible for the cracks on icy moons such as Charon, Saturn鈥檚 Dione and Tethys, and Uranus鈥� Ariel.
The key factor in determining if a crack is going to occur is the strain rate, the rate of pull from another body that would have caused the moons to deform at a rate that the top, icy layer could not sustain 鈥� leading to cracks.
Quillen鈥檚 and Ebinger鈥檚 co-authors on the paper are聽David Giannella and John G. Shaw, also at the University of聽Rochester.
In a companion paper, published in Monthly Notices of the Royal Astronomical Society, Quillen has shown that her models are consistent with the rate at which moons spin up or down when orbiting another object.”
The work聽was in part supported by NASA grant NNX13AI27G.
