A new study shows that Mars largest satellite Phobos shows signs of being torn by the extreme gravity exerted by the red planet.
Martian satellites orbit it
Researchers found that the unusual grooves covered on the surface of Phobos, which were previously believed to be scars left by the impact of ancient asteroids, were actually dusty canyons that became wider as the moon stretched under gravity.
According to NASA, Phobos is about 17 miles (27 kilometers) widest, it orbits Mars at a distance of 3,728 miles (6,000 kilometers) and completes three complete rotations around the red planet every day. By comparison, it is about 2159 miles (3475 kilometers) wide and 238855 miles (384400 kilometers) from the earth, and it takes about 27 days to complete a track orbit.
However, unlike the moon, Phobos' orbit around Mars is unstable: According to NASA, the tiny satellite is trapped in a death spiral and is slowly falling toward the surface of Mars at a rate of 6 feet (1.8 meters) every 100 years.
But Phobos's most unusual feature can be said to be its mysterious striped surface. Past theory generally believed that these stripes were formed at some point in the past when the asteroid hit Phobos, leaving a 6-mile (9.7 km) wide crater on the side, known as Stickney.
But a new study published on November 4 in the Journal of Planetary Science shows that these grooves may actually be caused by the moon being slowly torn apart by Mars' strong gravity as Phobos gets closer to the planet's surface.
The idea behind this new study is that as a celestial body (in this case Phobos) gets closer to a larger celestial body, such as Mars, smaller celestial bodies will begin to extend to larger objects. This is called tidal force .
In the case of Phobos, as Phobos approaches the surface of Mars, the tidal force applied to it is expected to increase until the end tidal force is greater than the gravity that holds the satellites together. Research shows that by then Phobos will be completely torn apart and the fragments may form a small ring around the planet, just like Saturn's ring .
Although previous studies have shown that tidal forces produce the tiger pattern of Phobos, the theory has been largely dismissed because the moon's powder or "fluffy" components are too soft to form such cracks.
Detailed image of Phobos surface stripes
In this new study, researchers used computer simulations to verify the idea that the moon's fluffy surface may lie on some degree of sticky sublayer. The simulations found that hard shells buried underground could form deep canyons where surface dust could fall into it, forming visible grooves on the surface. "Modeling Phobos into an interior of a ruble pile covered with a viscous layer, we found that tidal strain can produce regular spacing parallel cracks," the researchers wrote in the paper.
At the current speed, Phobos will complete the death spiral and hit Mars within about 40 million years. But if the tidal force had already torn the moon apart, the satellite might have been completely destroyed long before that.
In 2024, Japanese aerospace research and development agency JAXA will launch a new mission called "Martian Moon Exploration" (MMX), landing in Phobos and Tiansha . The sample returned in 2029 should reveal what happened to Phobos’ striped surface.
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