The strange mystery of Phobos’ tiger stripes may finally be solved

The Martian moon Phobos is not long for this universe.

According to astronomers’ calculations, the potato-like satellite is slowly, but inexorably, drawing closer to its host planet. Eventually, in 100 million years, the gravitational interaction between the two bodies will tear Phobos apart, giving the Red Planet a temporary dust ring.

According to a new study, these gravitational interactions may actually have a noticeable effect. At least some vaguely shallow and parallel furrows covering the moon The entire surface could be the result of rifting as its orbit slowly decays and tidal forces exert more force on its bones.

“Our analysis supports a heterogeneous layered structure of Phobos with potential core fractures caused by failure, as a precursor to the eventual extinction of the orbiting satellite,” wrote a team of astronomers led by Bin Cheng of Tsinghua University in China and the university. Arizona.

The tidal forces that pull on bodies in a system are the result of gravitational interaction, pulling their structures along an axis running between them.

Any significant effect this distortion would have on a hard surface is usually very small. Where tidal forces can be easily observed in the movements of our planet’s liquid oceans, the visible effects on land masses are less obvious.

This does not mean that tidal forces between other solid bodies cannot have more obvious consequences. The expansion caused by tidal forces can in some cases lead to stress cracking. We saw this in Saturn’s moon Enceladus, whose icy crust contains deep, parallel fractures at its south pole caused by tidal stress.

With an orbit of just 7 hours, 39 minutes, Phobos is very close to Mars, approaching at a rate of 1.8 cm per year. At that close, it’s entirely possible for tidal forces to crack the surface on its 27-kilometre (16.8-mile) body. The idea that the Phobos lines are the result of such an interaction has been considered previously and found plausible.

However, it is unclear whether the current formation and interaction between Phobos and Mars could have resulted in the observed band, and other explanations are in the works as well. For example, a 2018 study found that streaks could be the result of rolling rocks.

So Cheng and colleagues performed 3D mathematical modeling to explicitly examine the tidal expansion of a layered Phobos-like object, with a loose reddish outer surface sitting atop a cohesive layer below.

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

The team found that not all regions of Phobos were consistent with the model. In particular, about the grooves the moon The equator did not match expectations. But the results show that at least some of the lines can be caused by a fracture such as the moon Snails toward death by evisceration from the tides. This means that we are witnessing the beginning of the end for Phobos.

Therefore, these findings could have implications for the study of other moons that experience significant orbital decay, such as Neptune’s moon Triton. Drying out the debris could also reveal pristine material on Phobos, and the gullies could make a very interesting area to study for the next moon mission to Mars by the Japanese Space Agency.

This mission is expected to provide definitive evidence for the origin of these fuzzy streaks — but tidal disruption certainly seems like an intriguing possibility.

“Modeling Phobos as a pile of internal rubble encased in a cohesive layer, we found that tidal stress can create parallel cracks with uniform spacing,” the researchers wrote in their paper.

“Our analysis indicates that some of the grooves lining Phobos’ surface are likely early signs of the eventual demise of the out-of-orbit satellite.”

Mashed potatoes, anyone?

Research published in Planetary Science Journal.

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