The strange mystery of Phobos' Tiger Stripes may finally be solved

The strange mystery of Phobos’ Tiger Stripes may finally be solved

The Martian moon Phobos is not long in this universe.

According to astronomers’ calculations, the potato-shaped satellite is slowly but steadily approaching its host planet. Eventually, within about 100 million years, the gravitational interaction between the two bodies will tear Phobos apart, giving the red planet a temporary dusty ring.

According to a new study, these gravitational interactions could already have an observable effect. At least some of the mysterious parallel shallow grooves that cover each other of the moon The entire surface could be the result of a fracture as its orbit slowly disintegrates and the tidal forces increasingly tug at its bones.

“Our analysis supports a layered heterogeneous structure for Phobos with possible underlying failure-induced fractures as a precursor to the eventual demise of the deorbiting satellite,” write a team of astronomers led by Bin Cheng of Tsinghua University in China and the University of Arizona.

Tidal forces that pull on bodies in a system are the result of their gravitational interaction, stretching their structures along an axis that passes between them.

Usually, any significant effect this distortion might have on a solid surface is fairly small. Where tidal forces can be easily observed in the movements of our planet’s liquid oceans, visible effects on landmasses are less obvious.

That doesn’t mean that tidal forces between other solids can’t have more obvious consequences. Strain caused by tidal forces can, in some cases, lead to stress fractures. We’ve seen this in Saturn’s moon Enceladus, whose icy shell at its south pole shows deep, parallel fractures caused by tidal stress.

With an orbit of just 7 hours and 39 minutes, Phobos is fairly close to Mars, approaching at a rate of about 1.8 centimeters per year. This close, it’s entirely possible that tidal forces could crack the surface of the 17-mile-wide body. The idea that the stripes of Phobos are the result of such an interaction has also been considered before and found plausible.

However, it is unclear whether the current configuration and interaction of Phobos and Mars could produce the observed banding, and other explanations are also afoot. For example, a 2018 study found that the streaks could be the result of rolling boulders.

So Cheng and his colleagues performed 3D mathematical modeling that explicitly examined the tidal stretching and crushing of a layered Phobos-like body, with a loose, debris-like exterior sitting over a cohesive layer below.

The researchers ran hundreds of simulations with their model. In a significant number of these simulations, tidal forces caused the cohesive layer to split and fracture in parallel rilles, causing the upper loose regolith to flow into the fractures below. The result is a striped, striped surface very similar to regions observed on Phobos.

Not all areas of Phobos matched the model, the team found. Specifically grooves around of the moon Equator did not agree with forecasts. But the results show that at least some of the streaks could be caused by fractures the moon Spirals to death by tidal evisceration. This would mean that we are seeing the beginning of the end for Phobos.

These results could therefore have implications for the study of other moons undergoing significant orbital decay, such as Neptune’s moon Triton. The debris flowing off could also uncover pristine material on Phobos, making the rilles a very interesting study region for the Japan Space Agency’s upcoming Mars-to-Moon mission.

This mission aims to provide conclusive evidence as to the origin of these mysterious streaks – but tidal disturbances certainly seem an intriguing possibility.

“By modeling Phobos as an interior boulder pile overlaid by a cohesive layer, we find that tidal loading could produce regularly spaced parallel rifts,” the researchers write in their paper.

“Our analysis suggests that some of the ridges lining the surface of Phobos are likely early signs of the eventual sinking of the de-orbiting satellite.”

Mashed potatoes, anyone?

The research was published in The Planetary Science Journal.

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