Ever since the gargantuan cracks on Pluto’s moon Charon were first spotted, astronomers have been baffled as to what may have formed them, with explanations ranging from giant impacts to an active, hot mantle.
A new paper, due to be published in the journal Icarus, has come up with an alternative, and arguably more compelling, explanation: Based on a series of computer simulations, it appears that a long history of near-misses by other massive objects, and not plate tectonics, may be responsible for forging mountains and canyons on this distant world.
“I was inspired by computer graphics code in how to model the icy moons,” Alice Quillen, a professor of physics and astronomy at the University of Rochester and lead author of the study, said in a statement. “The 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.”
The computer simulations of the “close tidal encounters.” Alice Quillen via YouTube
Earth's Moon may be small, but it's still sufficiently sizable to be able to generate tides on Earth with its gravitational pull, both at the surface and within the liquid outer core. This mechanism is known as tidal forcing, and the authors of this new study hypothesized that this phenomenon may have once acted on the surfaces of icy worlds and moons like Charon when similarly sized worlds drifted close by in the Solar System, although they don't specify when this would have happened.
The researchers decided to use an N-body simulation, which models objects as having multiple internal regions interconnected by springs. It’s commonly used by astrophysicists to model the effect of gravity on planets and stars, but this is the first time it has been applied to a moon.
A massive perturber forming cracks on a Charon-like icy world. Alice Quillen via YouTube
In multiple virtual experiments, simulated icy moons were kept stationary as similar mass objects flew by them, and the team watched as they became deformed.
As it turns out, such close encounters exert enough of a tidal force on the icy moons to cause their surface to fracture in a brittle manner – and on surprisingly huge scales. This means that the giant cracks and complex fault structures on the icy moons of Dione and Tethys (of Saturn), Ariel (of Uranus), and Charon (of Pluto) at the very least may be caused by this mechanism.
A close-up of the tectonic belt on Charon. NASA/JHUAPL/SwRI
We know that Earth’s internal heat escapes through both volcanoes and, significantly, convection currents in the mantle; these move around tectonic plates, which create mountains, faults, canyons, ocean basins, and continents. This process is known as plate tectonics, and it’s been happening on Earth for at least 3 billion years, but there’s little evidence that it has happened anywhere else in the Solar System.
Icy moons like Charon are thought to be too small to still contain any heat left over from their presumably violent formation, so it’s unlikely that plate tectonics ever managed to effectively operate on them in the same way they did, and still do, on Earth. Perhaps this new study has finally solved the conundrum of where the ginormous alien crevasses come from – or, as another recent study suggested, these vast canyons may have instead formed as the icy moon cooled and contracted.
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