With all the science happening on and above Mars, it can be easy to forget the red planet has a pair of moons. And Mars could be down one moon in the distant future. NASA scientists believe Phobos is showing early signs of “structural failure.”

Check out the image below.

Phobos

See all those grooves? NASA scientists believe these grooves are the first sign that Phobos is failing.

“We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves,” said Terry Hurford of NASA’s Goddard Space Flight Center.

Phobos’ days might be numbered, but not anytime soon. Mars’ gravity is pulling in Phobos by 6.6 feet every hundred years. Estimates put the moon at being pulled apart at some time between the next 30 to 50 million years.

Understanding Phobos’ grooves

You see the massive crater on the lower right side of the image above? That’s Stickney crater and was long thought to be what caused the grooves. But a closer look at the grooves shows they don’t radiate outward from the crater, but from another area near it.

Scientists then theorized the grooves may be many smaller impacts of material ejected from Mars. Now, Hurford and his colleagues used modeling to show the gravitational tug of war between Mars and Phobos is responsible. The grooves are more like “stretch marks,” according to scientists. These tidal forces are slowly crushing the moon.

This new explanation isn’t new. When Viking sent the first images of Phobos to Earth decades ago, a similar explanation was proposed. But Phobos was thought to be completely solid. After calculating tidal forces, scientists back then found the stresses were too weak to break apart a moon of that size.

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Today, scientists believe Phobos interior is a bit weird. It’s not completely solid. Imagine a pile of rubble surrounded by a powdery layer of loose rock and dust about 330 feet thick. When Hurford and his colleagues used their model, predicted stress fractures were pretty close to the grooves seen in Phobos. This theory also helps explain why some grooves are younger than others. It makes sense if ongoing tidal forces are at play.

Now we just need to get a probe out there and find out what else is going on. Every rock in our solar system has an interesting story to tell. And Phobos’ story could even help researchers better understand planets outside our solar system.

“We can’t image those distant planets to see what’s going on, but this work can help us understand those systems, because any kind of planet falling into its host star could get torn apart in the same way,” said Hurford.

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